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Unread 02-15-2013, 07:56 PM   #1
motormike24
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4.2 tbi upgraded, but now i have issues. HELP!

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

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Unread 02-15-2013, 08:18 PM   #2
86cj74.2L
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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............
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Unread 02-15-2013, 08:25 PM   #3
CSP
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Do you hear the fuel pump prime when you first turn the key on?
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Unread 02-15-2013, 11:47 PM   #4
1986cj
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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.)
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Unread 02-16-2013, 08:33 AM   #5
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I think 1986cj is on to somethng there. It's starting on the ether since the spark plugs will still fire and when the key is released the computer has power.
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Unread 02-16-2013, 09:37 AM   #6
motormike24
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Quote:
Originally Posted by 86cj74.2L View Post
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
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Unread 02-16-2013, 09:40 AM   #7
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Do you hear the fuel pump prime when you first turn the key on?
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.
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Unread 02-16-2013, 10:29 AM   #8
1986cj
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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.
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Unread 02-16-2013, 10:37 AM   #9
motormike24
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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.
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.
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Unread 02-16-2013, 02:51 PM   #10
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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".............
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Unread 02-16-2013, 04:29 PM   #11
motormike24
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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.
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Unread 02-16-2013, 04:46 PM   #12
86cj74.2L
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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.
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Unread 02-16-2013, 05:08 PM   #13
motormike24
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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.)
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?
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Unread 02-17-2013, 12:58 PM   #14
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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!!!!!!!!!!!!!
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Unread 02-17-2013, 05:43 PM   #15
Jon In Tucson
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Quote:
Originally Posted by motormike24 View Post
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!!!!!!!!!!!!!
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
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