Jeep Enthusiast Forums banner

4.2 tbi upgraded, but now i have issues. HELP!

13K views 218 replies 13 participants last post by  motormike24 
#1 ·
hey guys. i've used this forum exclusively to do the complete GM tbi upgrade to my friend's 4.2 wrangler. it had the usual motorcraft carb swap already due to the crap carter carb that it came with smoked the old motor.

heres a brief rundown of what i've done til this point:

he had a rebuilt engine shipped to a shop that did his motor swap. drove it 200 miles or less with the motocraft carb. and burned up a piston in cyl 6. wasnt happy. called me cuz he was sick of the bs with the shop, and nobody would honor any warranty. I overnighted another engine kit, it has .060 over pistons in it, new rings, bearings, etc. then got it fired up, only to find the head musta been warped too. basically he got a junk rebuilt motor. so i swapped the head with a freshly machined head.

then he decided that since we could NOT get that damn ford carb to run worth a crap so he wanted to go FI. i researched options vs costs, again, from this wonderful site ;) and opted for the GM 4.3 tbi swap. i took the computer, MAP sensor, TPS, IAC, TBI unit, and temp sensor from a 92 chevy blazer 4.3. had a machine shop custom make me an adapter plate for the TBI.... but it wouldnt fire. found i had no injector spray. so i goosed it with some starting fluid, it fired, and like magic i suddenly had injectors! ran like a champ after some minor distributor adjustments. after we ran it around town we discovered it would lurch and pop and sputter at lower rpms, such as when driving 25-30mph in town in 3rd gear. but it ran perfect anything above 2500 rpms. never had a problem starting it again.

THEN, a few months later he decided he wanted to upgrade the distributor. i read about the HEI upgrade, and tried to do that. but could not obtain the proper distributor gear to run that set up within the time frame i had to work on his jeep. so we bought a brand new stock distributor, but got the ford distributor adapter and the ford 300 c.i. inline 6 distributor cap (because of it being bigger and farther spacing between posts). also ran with the TFI coil for better spark. went to fire it up, and no go. again, no injectors. so once again i goosed it with some spray, and it fired right up, and had great injectors as soon as it fired! kinda confused me, but figured it happened the first time, so no biggie. got the distributor timed properly, let it run a bit, then shut it off. i fired it up a few times, it was GREAT. i literally put a glass of water on the valve cover and it didnt move. went inside, drank some beers, and 4 hrs later came back to start it, no injectors. no matter how long it cranked. so i sprayed it AGAIN, and fired up and drove fine. shut it off, and it fired right back up. after lots of playing with it, i've discovered it will give injector signal every time to start it as long as its at least remotely warm. as soon as this winter weather cools it down, it loses its initial pulse signal to get it started. i dont understand. at all. ive changed the temp sensor with a new one, no change. the old distributor was JUNK i found out as it had many floppy parts and the magnetic deal that reads the star wheel under the rotor was constantly touching. but now that its got a good distributor it does this ****. HELP. im only here in town to help him out for a few days. im going the yard tomorrow to get a different computer in hopes maybe it was a freak coincidence that it went bad the same time i swapped the distributor, but i doubt it. please help me!

thanks, mike
 
See less See more
#2 ·
You don't have a scan tool?

Did you maintain the check engine light in the wiring harness? Is it on?

Are you accidentally feeding something important with the resistor wire that feeds the coil?

Are you accidentally feeding something important with either the choke circuit or the manifold heater circuit? These two circuits are fed with power from the oil pressure switch. No power Until it gets oil pressure which may explain why it will work once engine is running............
 
#6 ·
You don't have a scan tool?

Did you maintain the check engine light in the wiring harness? Is it on?

Are you accidentally feeding something important with the resistor wire that feeds the coil?

Are you accidentally feeding something important with either the choke circuit or the manifold heater circuit? These two circuits are fed with power from the oil pressure switch. No power Until it gets oil pressure which may explain why it will work once engine is running............
Well, no i did not retain the DLC as i created my own wiring harness with bulk spools of wire and a wiring diagram for the blazer. my buddy said he didnt care about a check engine light or a DLC cuz none of us have access to a scantool that will hook up to OBD1. The thing that throws me off is that before i replaced the distributor, it would start up fine all on its own without help from spray. after distributor, it wont when its cold. i really dont understand why it will warm, but not cold. it still has the original computer that came with the jeep with the nutter bypass done on it. and i verified that i hooked the cranking signal wire from the computer to the ignition signal wire that goes to the starter from the ignition switch. am i supposed to wire the oil pressure switch to the TBI computer as well? because i left that hooked up to the original jeep harness that i believe runs to either the gauge or to the computer (not sure how that circuit was wired from factory). this may be my issue if that is the case. let me know please.

mike
 
#7 ·
i opted not to use the relay and in tank pump. i chose to use an external inline pump E2000 part number (originally made for the ford e250 van) and hooked it up to a fused circuit from battery to a new switch in the cab to the pump. it turns on and has full pressure every time i flip the switch. so no fuel issues there.
 
#4 ·
Two things come to mind. You say that it will start and run if you spray starting fluid to it, and then you have the key in the run position it will keep running. Check that A6 from the computer is hot in both the start AND run position. Hot in the run only will not send power the injectors in the start position. Second, C9 is hooked up to the "S" post on the starter relay ( Tells the computer that you are trying to start the engine and will release the ground to the injectors in the start position.)
 
#13 ·
the only part im fuzzy on here is a lot of starters have an S post and an I post on the solenoid. i've got my C9 hooked to the same wire that feeds the starter from the ignition switch. thats the correct way to do it right? or is it sposed to go on the opposite terminal?
 
#8 ·
Test your injectors. Unclip the plug to the injector and with a simple test light you will have power to the red and white wires with the key on with a engine ground. Do you have the same power with the key in the start position or does the light go out? Test the plug with the red wire and get your ground from the blue or green wire and the light will pulse when cranking. The red and white wires have power in key on and start position, the green and blue wires supply the ground from the ecm. Just having power to the red or white wire with a engine ground doesn't mean the injectors will work. Depending on where you got your constant hot and switched hot the oil switch will have nothing to do with it.
 
#9 ·
I'm not a fan of tapping into existing wiring, so i ended up wiring up my own rig for most of it. i have the constant hot wires to the ECM running through a fuse and straight to the battery positive. the switched wires are ran thru a fuse, to another switch in the cab, and then to the battery positive. i turn on the fuel pump switch to prime the system, then the ecm switch, wait 2 seconds, and then crank it, and it fires right up. unless it cooled down too much. also, i have no injector pulse until it fires the very first time, then they pop on instantly.
 
#10 ·
GM products of those years will flash diagnostic codes with the check engine light when you jumper two pins on the ALDA connector.

How can you trouble shoot anything without a scanner? All you can check is spark and fuel pressure.

It's just "hope and poke", and "when in doubt swap it out".............
 
#11 ·
GM products of those years will flash diagnostic codes with the check engine light when you jumper two pins on the ALDA connector.

How can you trouble shoot anything without a scanner? All you can check is spark and fuel pressure.

It's just "hope and poke", and "when in doubt swap it out".............
i highly doubt that even if i had hooked up an alda connector, and the check engine light, that it would tell me why my injectors dont pulse until first ignition... just saying... never seen a code like that.
 
#12 ·
This is true........but down the road when a temp sensor fails and your mixture goes rich and you start gassing the oil you will have no clue that the PCM thinks its 25 outside when its 85 or or what not.

Not saying it will help you now just that any problem your flying blind.

If GM is like Chrysler it would tell you that the feed circuit is missing for the injectors as a trouble code. But you will never know as it is now.
 
#14 ·
so i have now replaced the ecm with another junkyard ecm, the truck had a blown engine, so im assuming the ECM is in good health. It was a 91 chevy s10 2wd tbi 4.3 manual trans. this jeep is a stick, so i figured maybe it mattered that the previous ecm was from an automatic. maybe not. pulled jeep into garage, swapped the computers, and it fired up INSTANTLY, like barely have a revolution and it fired and actually idled perfect. this thing was having a 1600 rpm idle once it got warm but only since i put a new distributor into it. it would idle 900 rpm cold, then when it would hit 160 or 180 degrees, it would jump to high idle mode at around 1600. now, it will run smooth at 900 warm. so maybe computer was bad after all. however, im still having the issue that once i shut it off, i can instantly restart it and see the injectors spraying a very small amount of fuel during cranking. but if i shut it off, and wait 5 mins, it squirts like a drop and then nothing, and wont fire without sprayin ether in it. it no longer seems to matter warm or cold. and even if i leave the fuel pump running the whole time i let it sit, i turn the switched 12v circuit for the ecm on, and crank it over, it drops a single drop of fuel and then quits spraying period unless i spray it. im so befuddled its rediculus. but i can start and stop and start and stop no problem. help!!!!!!!!!!!!!
 
#15 ·
Your best bet is to go over to the IH forum, Binderplanet.com and look at the injection tech section. The moderator, BillUSN1 is a wealth of knowledge in regards to TBI conversions, and doesn't give us Jeep guys too much ribbing...

To even to begin to troubleshoot your warm start problem, I think you need to monitor the SES light from connector pins A6 to A5. If you don't have the ALDL connector at least jumper pins A9 to A12 to put in diagnostic mode to see whats going on.
OBD1 systems don't need a lot of fancy diagnostic tools, mostly a good multi meter and knowing how to use it. God bless.
Jon In Tucson
 
#17 ·
I would want to see what temps the PCM thinks its seeing. Both engine temp and intake / throttle body temp. Sometimes the throttle body temp is used to calculate its warm start parameters. If their not within 10 degrees of each other and within 10 degrees of ambient temps they need replaced.

You have power at ignition on to the injectors, and what not? Reason I ask is because there is a feed circuit in that engine bay that only gets power after the engine is running. It's off the oil pressure switch.
 
#18 ·
I would want to see what temps the PCM thinks its seeing. Both engine temp and intake / throttle body temp. Sometimes the throttle body temp is used to calculate its warm start parameters. If their not within 10 degrees of each other and within 10 degrees of ambient temps they need replaced.

You have power at ignition on to the injectors, and what not? Reason I ask is because there is a feed circuit in that engine bay that only gets power after the engine is running. It's off the oil pressure switch.
i will check for power during "key on" to inejectors, but id have to assume it does since it will pulse injectors just fine to start up when warm. i dont see how temp would affect the power from ecm to injectors. as far as the circuit u referred to from the oil pressure switch, where does that run to, as my GM ecm is not tied into the oil pressure switch at all as of now. its a one wire sending unit, so im assuming that runs directly to the factory oil gauge, right? and if it IS supposed to be connected to my new ecm somehow, why was it starting in all temp ranges with no problem before i swapped the distributor, but not after? im still stuck on that part. because if i understand the gm system correctly, the ecm uses the signal from the coil primaries to pulse the injectors, right? if thats the case, im thinking there must be an issue that is related to that but im still confused at why it would be affected by temp. today is my last day in town at my buddies place so it'd be really cool if i could get this figured out, lol. thanks.
 
#21 ·
You need a manual to see where the wires are. There are some in PDF format here somewhere.

They fed the electric choke and the intake heater and were on the oil switch to ensure their we're only energized after the engine was running.
but wouldnt that all be run from the stock jeep computer? i followed several write ups for doing the ecm wire harness, and i dont recall reading anything that said to tie the GM ecm into the oil pressure switch... someone suggested that maybe part of the GM ignition module is fried?
 
#20 ·
The temp sensors are used to determine which fuel map to use during a start condition. As an example.

There are a few scanners out there that will read OBD1 as well as software to load on your laptop. Running fuel injection without being able to see what it's seeing and having access to the trouble codes makes it awfully hard to figure out what's wrong.
 
#22 ·
There is no stock Jeep computer. A pressure switch relies on oil pressure to be built before the switch closes and contact is made. This technology pre-dates computers being used. I'm not sure what power feed is being referred to, but that's how it works.
 
#24 ·
there IS a stock jeep computer. thats what ran the original carter carb that was on it, as well as the intake heater, o2 sensor, distributor, etc. otherwise there would be no way to control spark without points. also, if there was no stock computer, how would the nutter bypass have come about? not trying to be an ***, just saying there IS a computer because i relocated it to the drivers fenderwell. also did the nutter bypass. but currently i have both the GM ignition module AND the factory ECM hooked to the coil primary wires (positive and negative feeds). maybe thats part of my issue?
 
#26 ·
The point you blew right over is that the stock computer, which you've removed 99% of what it did by removing the feedback carb, had nothing to do with a pressure switch activating circuits.

BTW, the ignition module controls spark. Every CJ from '78 through the 90 YJ has the same one and pre-81 CJ's didn't have any kind of computer.
 
#27 ·
well here's an update. On a far fetched hunch, i was prompted by several people to replace the GM ingition module that i had spliced into the whole TBI rig. i figured, if that was bad i'd have to lose spark. i mean, after all, isnt spark the entire job of that module in this particular setup? but, i had great spark, right on time. however, since my last post, i had put a timing light on the crank, and found that the ignition timing was 15 degrees too early. so i adjusted the distributor, and set timing to 10 degrees BTDC. seemed to run much better, my lack of torque past 2000 rpm seemed to mostly go away, but still had the slightly off beat idle (almost like it was still out of time). still wouldnt start when cold. not one drop came out of the injectors upon cold crank. so i bought another ignition module (new), and hooked it up. boom fired right up, BUT the temp was already 130 degrees. so not guaranteed that fixed it. most of the time, even at full operating temp, it would crank 6 or 8 times be4 firing. this time, it barely cranked twice and fired. so i let it get cold again. cranked and cranked, no fire. so i pulled the air cleaner, and loah and behold the throttle plates were soaked. definately had fuel this time. sprayed starting fluid in case it wasnt enough fuel getting to the cylinders. still no fire. so held it at wide open throttle, and after 4 or 5 cranks it roared to life, but wouldnt hold an idle unless i kept my foot slightly on the gas for 15 seconds. then it would idle. but it runs like crap when cold but kinda ok when its hot. so im thinkin i fixed the no fuel during crank problem, but now maybe the distibutor needs to be re-timed? what do you guys think?
 
#28 ·
so, last night, before i had a chance to bring the jeep in the garage to mess with the timing some more, i had another car i needed parts for. the jeep wouldnt start, with fluid or otherwise, however it seems that it was spraying fuel during cold start, FINALLY. however, i lost all spark. this was AFTER i replaced the GM ignition module. i still had the old one mounted to the body, and had the new one taped to the top of it til i could get it in the garage and properly mount the new one. so, just tryin to figure out why the hell i lost spark in less than an hour after installing the new module, i hooked the old crappy one back up. it fired up immediately. ran like crap, but at least it ran. i barely made it to the store and back, stalled several times. i understand new parts can be defective, but jeez, is there something that could possibly be killing these modules??? help please!
 
#30 ·
i got the BWD brand (borq warner), and now it starts, but im back to square one. :( still only sends fuel warm. is there a way that maybe i can completely run the spark and fuel control from the GM computer, without needing the factory jeep computer hooked up via the nutter bypass? it seems i remember at one point trying to do that, but as soon as i clipped the wires comming from the jeep computer, it wouldnt run anymore. maybe not, idk. im just so frustrated with this seemingly simple design. and ive tried unplugging temp sensors, and pluggin em in again, nothin seems to affect this issue. except temperature.
 
#31 ·
If your nutter bypass was done correctly since your running fuel injection you should be able to remove the mcu completely with no effect.

Are you using the red #10 wire that feed the DuraSpark ignition module as the power feed for the PCM, injector power source, and your HEI setup?
 
#34 ·
If your nutter bypass was done correctly since your running fuel injection you should be able to remove the mcu completely with no effect.

Are you using the red #10 wire that feed the DuraSpark ignition module as the power feed for the PCM, injector power source, and your HEI setup?
i guess im not sure what the "duraspark" is, but i do not have anything running off the power feed for the ignition module im using. (which is the one for a 91 chevy s10 4.3) and i do not have an HEI setup, i opted to go with the bigger ford cap/adapter setup with the TFI coil.
 
#32 ·
Exactly, the stock computer shouldn't be in the loop anymore.

As has been said multiple times, you need to figure out what the TBI computer is seeing to really diagnose what's going on. Your wiring sounds like a complete crapshoot, so who knows how to diagnose what is going on.
 
#33 ·
I'm just going to throw this out there.A while back a member was having cold start problems with his Howell.He had them for 2 winters in a row.Summer time he was fine.After his engine warmed up it would start everytime.Simplest thing,it turned out to be the battery.Just me 2cent worth.
 
#35 ·
Are you or are you not using a HEI module for spark?

The factory ignition was the DuraSpark (Ford) ignition located on the drivers side fender down low. It has two roundish plugs. One of them is a fat #10 wire. That wire is what I would use to feed power to everything associated with the fuel injection. Ignition included.

If you unplug the MCU with the engine running and the Engine shut off while running off the GM fuel injection and ignition you just installed you did something wrong.

If you think the check engine light and the ALDA connector is not needed how much do you really understand about engine management systems and how fuel injection works and especially how all them sensors interact with each other.

Learning to read wiring schematics is key to doing what your trying to accomplish. It's nice to just do what you saw in the Internet. Troubleshooting is a whole nother animal when things go wrong.

I'm not trying to be a jerk on purpose but some have asked what your using for power feeds to certain wires and you never answered them to my knowledge. Or me for that matter.

To me the only benefit of fuel injection is the cold starting. It is better for four wheeling than a carb and it easily passes emissions as well.

But their is nothing simpler than a carb that's operating properly and a stand alone ignition system. To my knowledge no one with fuel injection has ever got stellar mpg. Let alone better then some of us running carbs and getting 18 to 20 mpg. (One guy in Canada gets 22 to 23)
 
#36 ·
Are you or are you not using a HEI module for spark?

The factory ignition was the DuraSpark (Ford) ignition located on the drivers side fender down low. It has two roundish plugs. One of them is a fat #10 wire. That wire is what I would use to feed power to everything associated with the fuel injection. Ignition included.

If you unplug the MCU with the engine running and the Engine shut off while running off the GM fuel injection and ignition you just installed you did something wrong.

If you think the check engine light and the ALDA connector is not needed how much do you really understand about engine management systems and how fuel injection works and especially how all them sensors interact with each other.

Learning to read wiring schematics is key to doing what your trying to accomplish. It's nice to just do what you saw in the Internet. Troubleshooting is a whole nother animal when things go wrong.

I'm not trying to be a jerk on purpose but some have asked what your using for power feeds to certain wires and you never answered them to my knowledge. Or me for that matter.

To me the only benefit of fuel injection is the cold starting. It is better for four wheeling than a carb and it easily passes emissions as well.

But their is nothing simpler than a carb that's operating properly and a stand alone ignition system. To my knowledge no one with fuel injection has ever got stellar mpg. Let alone better then some of us running carbs and getting 18 to 20 mpg. (One guy in Canada gets 22 to 23)
no, im not using HEI, as i said. i was going to originally but could not locate all the pieces i needed fast enough, so i stuck with the originial jeep distributor (but replaced it with OEM new), and added the ford distributor cap adapter and the larger ford cap and wires. we arent worried about fuel economy. we want instant startup regardless of weather and more power. which it seems to have accomplished until this little issue. and im thinking you skipped over the several spots i mentioned i have NOTHING tied to the factory ignition switch except the starter signal wire which also has the c9 gm computer connection tied to it so the computer knows when its cranking over to start. that being said, i have 2 add-on switches i put into the dashboard. one of them runs as follows: battery positive, inline fuse, then into switch. the output of the switch goes directly to positive on external fuel pump. the next switch runs from battery, inline fuse, to switch. the output of that switch goes directly to the key-on power for the GM ecm. the constant power wire for ecm has an inline fuse also and goes directly to positive on battery. that way i didnt have to mess with anything in the steering column. when i go out of town to work on this guys jeep, i usually only have a couple days at a time, so you can frown upon my methods all you want but i had good reason to cut certain corners. got the same results doing it that way as i would have tying into the ignition switch. plus easier to diagnose if one or the other fails. there is a tan wire that goes from the computer to the 4 wire plugin on GM igition module that i had to disconnect in order to let it run properly. not sure what that runs without going back over the schematic, but if its hooked up it runs like **** and cant hardly keep it running, if i cut it, runs fine. so i left it unhooked. not sure if maybe its fighting the nutter bypass when hooked up or what.
 
#38 ·
What is making the spark? Your using the factory distributor which is ok.

Where is your ignition module?

What feed are you using for the injectors? One of your installed switches?
the GM ecm run the injectors. the ignition module (GM) is mounted on the passenger side fenderwell, with the heat putty between the heatsink and the body of the jeep. it has a 4 wire connector comming from the computer, which is where i mentioned i had to cut the tan wire to make it run right. also has a 2 pin connector next to that, and i dont remember off the top of my head where that goes to. and on the opposite end of the module, theres 2 prongs sticking out of it, which go to the coil pimaries. i also have the jeep computer (nutter bypass) spliced into the same coil primaries. and again, the only reason i had spliced those wires back into this setup is because it would not run when i first hooked it all up without them. maybe i misunderstood the write up for doing the tbi wiring for the ignition module, but idk. i THINK i did it right minus the lack of ALDL connector and ck engine light.
 
#42 ·
He's using a mix of the 8-pin GM ignition module and the factory ignition somehow. The 8-pin isn't wired correctly at all.

the GM ecm run the injectors. the ignition module (GM) is mounted on the passenger side fenderwell, with the heat putty between the heatsink and the body of the jeep. it has a 4 wire connector comming from the computer, which is where i mentioned i had to cut the tan wire to make it run right. also has a 2 pin connector next to that, and i dont remember off the top of my head where that goes to. and on the opposite end of the module, theres 2 prongs sticking out of it, which go to the coil pimaries. i also have the jeep computer (nutter bypass) spliced into the same coil primaries. and again, the only reason i had spliced those wires back into this setup is because it would not run when i first hooked it all up without them. maybe i misunderstood the write up for doing the tbi wiring for the ignition module, but idk. i THINK i did it right minus the lack of ALDL connector and ck engine light.
Here's how it shold be wired. The two wire connector right next to the four wire connector should be wired to the coil. The two on the other side of the module should go to the orange and purple wires that come from the distributor. The factory ignition module should be in the trash at this point.
 

Attachments

#40 ·
The wires you cut from the ECU when it stopped, were they orange and purple?

The original computer was mounted above the glove box and referred to as the MCU I believe. The mcu controlled the spark and the carb yes. When you nuttered it you ran a purple and orange from the distributor over to the drivers side fender to the ignition module (DuraSpark).
 
#41 ·
The wires you cut from the ECU when it stopped, were they orange and purple?

The original computer was mounted above the glove box and referred to as the MCU I believe. The mcu controlled the spark and the carb yes. When you nuttered it you ran a purple and orange from the distributor over to the drivers side fender to the ignition module (DuraSpark).
yes orange and purple, but im not sure exactly where this duraspark thing is ur talking about. maybe i did that part wrong too, cuz i just ran new wires directly from the mcu to the coil.... X( maybe i got it alllll kindsa goofed.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top