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YJ stalls under load Howell TBI 4.2 manual transmission

666 Views 15 Replies 6 Participants Last post by  MrTrash

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.
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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.
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