[MrTrash]

Hello,

Recently purchased a 1988 Jeep YJ 4.2 manual with a Howell TBI conversion stalls under load. California Version.

History of the Jeep is unknown but has a Howell TBI that looks almost new, almost like it was never run. The vacuum routing was a bit wonky when I got the Jeep. The MAP sensor was wired but not connected to the TBI. The distributor was not connected to the TBI and there was a cap over ”filter to atmosphere“ port on the TBI. the other sensors all had power when running. the electrical connects all appear to be sound.

I have been through the Howell install manual and all the connections appear correct. I checked as best I could for vacuum leaks with propane. I connected a gauge to the constant vac source on the TBI and it held pretty steady at 15/in hg. there is power to the MAP sensor and good power to the three fuses in the fuse box under the dashboard. I replaced the fuel filter as a precaution and fuel pressure is strong (I could not get a good reading). The jets have a good spray pattern. I added about 5 gals of fuel just in case the fuel was funky. Distributor is pointing to the number 1 cylinder at TDC. The timing is about 8 degrees.

the engine fires right up when cold and idles at about 950 rpm accordimg to the dash tach.

i haven’t been able to pull any codes from the OBD1 port or check if there is any issue with the fuel return.

any ideas for me? the problem is so bad that the jeep stalls every time I try to leave the driveway.

thanks in advance.
Matt

 

[timatoe]

Still running the stock distributor? I know the factory spec is 8* BTDC but you may try bumping it 12-13 and see how it does. Mine won't stay running at 8, but runs like a champ at 13. It's easy and free.

 

[Boojo35]

howell tbi timing question

i just installed the new unit on my 83 4.2l and the timing is way low do i have to unplug something before i can adjust the timing on the new set up,or do i just adjust the timing and then turn down the idol?

www.jeepforum.com

See post 4 on how to set your timing. You may have it retarded if you did not follow this procedure.

15 in hg vacuum at idle is low. retarded timing can cause that.

Using a fuel pressure gauge to verify your fuel pressure is a good idea.

Is your MAP sensor connected to intake or ported vacuum? It should be to intake vacuum.

 

[timatoe]

Post #4 in the above link is for setting idle speed, if someone has dicked with that you need to get it dialed in, but not needed for the timing. Still not a bad thing to double check.

 

[Boojo35]

But don't you have to ground pin A to B on the distributor to set the timing on a howell? It is common practice to have to do so on other GM TBI systems. It puts them into base timing mode. Also. vacuum advance has to be disconnected.

I cannot say for sure if this is needed on a howell, but would not be surprised.

 

[93YJ4FUN]

@Shop Gumby clarification is needed. Not sure if he's still in the virtual area though.

 

[timatoe]

Timing is set with the vacuum disconnected but there's no need for the jumper (at least I've never used it). The section he pulled that from specifically says it's for idle air control (not really idle speed like I previously said).

This is all they say about setting timing.

My theory would be that it is because the computer in the Howell system doesn't actually control timing like it does in stock GM versions.

 

[bpounds]

The Howell system doesn't know anything about ignition, other than a tach signal to indicate that it is cranking. The injectors won't fire if there isn't a tach signal. The thing involving grounding A-B is to set the base idle, not related to timing.

Assuming you have a base idle of around 750, just set timing with a light and with the vacuum advance disconnected and the hose capped off. Idle isn't critical here, but you don't want it so high that the mechanical advance might pull in.

I've run my timing at various points over time. Never made any big difference to performance. Howell specifices 8° BTDC ± 2° and it is on the emissions sticker. That might be important if you are in CA and need a smog test. I've run between 8 and 12 and like I said never saw much difference, and that was with the original distributor (nuttered) as well as with the GM HEI that I have now. I've settled on 10° which gets me past the smog test okay.

My vacuum runs 18 - 20 in/hg with a well sealed intake manifold.

Having said all that, based on my experience, I don't think timing will end up being your issue, but of course you do need to check it. Check your vacuum level on port 'A' which is the front facing throttle body port. I'm suspicious of your vacuum. The intake manifold can be tricky to get well sealed. There is also a difficult to seal point under the throttle body around a bolt through the base adapter. You would have to pull the TBI to check it. Supposed to have a mound of RTV which is easy to screw up and hard to find if you do.

Lastly, since I've been dealing with this myself lately, I would check fuel pressure and volume.

 

[MrTrash]

thanks for the replies. Based on the input here, I went back checked the timing and rechecked the vacuum at ‘A‘. I adjusted the timing and the engine seemed to run the best at 8* BTDC. The major finding was I found zero vacuum ’A’. To double check the gauge, I held the tube to my hand I could feel zero suction. When I revved the engine it would jump to 20 in/hg or so, but it was reading zero at idle.

I did the initial check in the dark after work and rushed it and didn’t notice my gauge was not zeroed.

I ran out of time and did not have a chance to pull the TBI to check the seal and if the RTV was mounded as Howell instructed. That bad of a leak makes me suspect that it is more than just the TBI. I will report back.

the good news is that I have darn near checked everything else on this jeep and otherwise all seems to be well. It has good compression and It appears that the TBI is plumbed and wired correctly.

thansk again for the valuable feedback.
matt

 

[Shop Gumby]

thanks for the replies. Based on the input here, I went back checked the timing and rechecked the vacuum at ‘A‘. I adjusted the timing and the engine seemed to run the best at 8* BTDC. The major finding was I found zero vacuum ’A’. To double check the gauge, I held the tube to my hand I could feel zero suction. When I revved the engine it would jump to 20 in/hg or so, but it was reading zero at idle.

I did the initial check in the dark after work and rushed it and didn’t notice my gauge was not zeroed.

I ran out of time and did not have a chance to pull the TBI to check the seal and if the RTV was mounded as Howell instructed. That bad of a leak makes me suspect that it is more than just the TBI. I will report back.

the good news is that I have darn near checked everything else on this jeep and otherwise all seems to be well. It has good compression and It appears that the TBI is plumbed and wired correctly.

thansk again for the valuable feedback.
matt

@Shop Gumby clarification is needed. Not sure if he's still in the virtual area though.

Just saw this thread, (93YJ4FUN trying to interrupt my first coffee of the day?) and from a quick read-through a few things popped up. Regarding vacuum ports, the port on the rear of the throttle body between the fuel fittings is made for the MAP sensor, and the sensor only. Nothing else should be tapped into that line. Be sure to mount the sensor so it's above the port, otherwise the vapors, fumes etc., can accumulate oil and fuel in the line, eventually getting into the sensor. The front ports are a bit more complicated. There are several different port configurations on otherwise identical throttle bodies. They vary depending on their original application, vehicle etc., but almost all will work the same. The large port poking out the front center is for pcv only (C in casting). Directly under the pcv port and slightly to the right, looking at it from the front, is a ported vacuum fitting (A in casting). This port should have little to no suction at idle. It's routed through a slot/orifice just above the throttle plates when closed, which gives no signal. When the throttle is cracked open slightly, these slots are exposed to manifold vacuum. As the throttle is gradually opened all the way, they will eventually match whatever vacuum signal the manifold is making. The other two on either side (J and S) are where the variations come in. Some tb's have just a boss in the casting, with no fittings from the factory. I drill and install at least one before they go out to customers, since they both are designed for manifold vacuum. Sometimes GM installed just one. Sometimes they installed both. Sometimes they are both small fittings, other times they are larger. And there are also versions with both types, just to make things interesting. If the previous owner followed directions, the California emissions sticker included with the kit should be somewhere under the hood so you can get the vacuum line routing correct, and the brass E.O. smog tag should be screwed to the side of the tb just ahead of the throttle linkage bracket. I could keep blathering on, but those are the basics, and hopefully it will help get you going. I'll keep tabs on this thread just in case more blathering is requested

 

[MrTrash]

Just saw this thread, (93YJ4FUN trying to interrupt my first coffee of the day?) and from a quick read-through a few things popped up. Regarding vacuum ports, the port on the rear of the throttle body between the fuel fittings is made for the MAP sensor, and the sensor only. Nothing else should be tapped into that line. Be sure to mount the sensor so it's above the port, otherwise the vapors, fumes etc., can accumulate oil and fuel in the line, eventually getting into the sensor. The front ports are a bit more complicated. There are several different port configurations on otherwise identical throttle bodies. They vary depending on their original application, vehicle etc., but almost all will work the same. The large port poking out the front center is for pcv only (C in casting). Directly under the pcv port and slightly to the right, looking at it from the front, is a ported vacuum fitting (A in casting). This port should have little to no suction at idle. It's routed through a slot/orifice just above the throttle plates when closed, which gives no signal. When the throttle is cracked open slightly, these slots are exposed to manifold vacuum. As the throttle is gradually opened all the way, they will eventually match whatever vacuum signal the manifold is making. The other two on either side (J and S) are where the variations come in. Some tb's have just a boss in the casting, with no fittings from the factory. I drill and install at least one before they go out to customers, since they both are designed for manifold vacuum. Sometimes GM installed just one. Sometimes they installed both. Sometimes they are both small fittings, other times they are larger. And there are also versions with both types, just to make things interesting. If the previous owner followed directions, the California emissions sticker included with the kit should be somewhere under the hood so you can get the vacuum line routing correct, and the brass E.O. smog tag should be screwed to the side of the tb just ahead of the throttle linkage bracket. I could keep blathering on, but those are the basics, and hopefully it will help get you going. I'll keep tabs on this thread just in case more blathering is requested

thanks for the timely clarification. Where is the best fitting to check the idle vacuum? The brake booster?

Map sensor is connected to the port between the fuel lines and is a dedicated hose

“c” port has the line to the front PCV fitting.

Ported vacuum is at “A“ going to CTO valve. This is where I checked vacuum, but it looks like it is normal to have zero vacuum at idle here.

no hood sticker was placed but it does have the brass EO fitting. I checked all the vac connections against the Howell install manual and all should be corr3 t.

thanks again for the hep,
matt

 

[93YJ4FUN]

for Gumby.

 

[Shop Gumby]

If you have a scanner, you can also check running voltage to the fuel pump, tps and map sensors, and battery voltage. Might be a long shot, but if any of these are erratic it could be causing your issue. Also if voltage gets low enough, it'll affect how the ecm behaves. The official Howell test mule Jeep here has similar symptoms, but only occasionally and it's somewhere other than the fuel injection. (Can't be having that!) It gets irritating when plowing snow for sure, I'm thinking the distributor or maybe even the Duraspark module, since they are both original and have a LOT of miles. Keep at it, you'll sort it out
- Dan

 

[Shop Gumby]

for Gumby.

Thank you, fine sir. Now where did I put that Baileys.......

 

[MrTrash]

If you have a scanner, you can also check running voltage to the fuel pump, tps and map sensors, and battery voltage. Might be a long shot, but if any of these are erratic it could be causing your issue. Also if voltage gets low enough, it'll affect how the ecm behaves. The official Howell test mule Jeep here has similar symptoms, but only occasionally and it's somewhere other than the fuel injection. (Can't be having that!) It gets irritating when plowing snow for sure, I'm thinking the distributor or maybe even the Duraspark module, since they are both original and have a LOT of miles. Keep at it, you'll sort it out
- Dan

thanks for the info. I checked the vacuum at “J” and got a pretty steady reading of 19-20 in/hg. I am more and more convinced it is not the Howell, not a vacuum leak and not a timing issue. like you suggest it could be one of those things. it Might even be the clutch. How do I tell if that is going out?

matt

 

[MrTrash]

Hello,

wanted to post the resolution. I event brought the Jeep to the mechanic. He replaced the fuel pump. He said the pump had some sort of short that cropped up only under load.