Howell Tbi troubleshooting questions and HELP

Crush 4

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Mudsters

Need the collective minds and wisdom of mud nation

Couple of disclaimers. I am a rookie mechanic. I have spent hours researching on line forums and am a rated pest on the Howell hot line. To say I have asked too many questions is an understatement.

The system was put on about 10 years ago on my 75 FJ 40 2F. I believe by Sam’s off road in Cali. Did it. When I bought the vehicle 3 years ago it ran ok but eventually it started to start and run rough, including sputtering, bogging no power and intermittent stalling. Here is what I have tried so far:

-adjust FP to spec 11-13
-adjust timing, tried several settings
- has dui distributor
-checked for vacuum leaks. Replaced some lines anyway
- moved map sensor vacuum to back of TB and above TB. It runs better w map in front of TB, head scratcher.
-replaced map sensor and ecm as a result of pulling codes 33&34
- replaced fuel filter
- removed gas cap as I read this can helo venting?

Through each phase of these updates there has not been much improvement .

Needless to say I’m frustrated as it shouldn’t be this difficult, should it?

Any help would be greatly appreciated or should I just replace it with a holly sniper LOL
 
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Those TBI setups are super simple and work great in general. Had one on my early Wrangler and really liked it. Sounds like you've replaced a decent amount of stuff. How about the injector setup? A clogged injector could cause the issues you are seeing.
 

Crush 4

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Those TBI setups are super simple and work great in general. Had one on my early Wrangler and really liked it. Sounds like you've replaced a decent amount of stuff. How about the injector setup? A clogged injector could cause the issues you are seeing.
What is best way to troubleshoot that? Of course I’ll google as well👍
 
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You could have them flow tested/cleaned. But for like 25 bucks a piece would probably just replace them. Heck the entire throttle body is like 250 and would take care of those, plus the regulator diaphragm and other wear items. Just not a lot of parts to that system. Unless you have a bad ground or something its not that much $$ to throw parts at it until it works.

I've had both the Howell and Sniper setups. The Sniper is neat, but other than tunability doesn't run any better than the Howell one. And the Howell setup is nice because its basically all off the shelf GM parts you can get anywhere. Would try to keep it if you can.
 

Crush 4

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You could have them flow tested/cleaned. But for like 25 bucks a piece would probably just replace them. Heck the entire throttle body is like 250 and would take care of those, plus the regulator diaphragm and other wear items. Just not a lot of parts to that system. Unless you have a bad ground or something its not that much $$ to throw parts at it until it works.

I've had both the Howell and Sniper setups. The Sniper is neat, but other than tunability doesn't run any better than the Howell one. And the Howell setup is nice because its basically all off the shelf GM parts you can get anywhere. Would try to keep it if you can.
In terms of bad grounds. I have come across that in the multitude of stuff I have read but not sure I understand how to troubleshoot and fix? I’ll take any ideas!

Als I have been researching injector trouble shooting including usin node lights/9v batteries and timing lights. Any thoughts here? As far as I can tell the injectors are working, meaning at idle truck runs decent and when I rev it truck revs fine. If I stab the gas throttle it stalls/ Boggs.

Thx for suggestions so far
 
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While these systems are pretty robust, they are picky about voltage. A bad ground or even weak battery can cause both the codes you pulled. Best bet is to just check the harness for obvious trauma, and pull all the grounds and clean them up.

I've never tried to diagnose a bad injector. Always just replaced if suspect.

Have you checked fuel pressure when you rev it (ie not just at idle)? Like I said, the FPR in the throttle body is a rubber diaphragm thing that can go bad over time. I would think it would go bad at all RPM but who knows. Bout $20 to replace it but would see if you can measure pressure as it tries to stall first.
 

Crush 4

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While these systems are pretty robust, they are picky about voltage. A bad ground or even weak battery can cause both the codes you pulled. Best bet is to just check the harness for obvious trauma, and pull all the grounds and clean them up.

I've never tried to diagnose a bad injector. Always just replaced if suspect.

Have you checked fuel pressure when you rev it (ie not just at idle)? Like I said, the FPR in the throttle body is a rubber diaphragm thing that can go bad over time. I would think it would go bad at all RPM but who knows. Bout $20 to replace it but would see if you can measure pressure as it tries to stall first.
For clarity, there is only one ground correct? I did clean it and made some changes on how it’s bolted to the block.
In terms of FP I did check it at idle and I think under rev. What would be symptoms if FP dropped under rev?
I’ll test drive w new ground set up tomorrow if no luck on to injectors and TB.
Stay tuned
 
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No idea how many grounds. Assume every Howell harness is a bit different (mine was on a Jeep 4.2L).

I would assume a bad FPR could cause stumbling but really depends on how its failing. The TBI setup has a diaphragm and spring that reacts to vacuum pressure if I remember correctly. So when the diaphragm goes bad, it doesn't react properly under load.

Looks something like this


Could be entirely off track but again, only so many moving parts there to fail. Pretty simple system.
 

Crush 4

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Do you guys think the fuel level can impact performance? Meaning if my gas tank is only got a couple gallons in it? Just thinking out loud
 
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If the fuel pump were weak and/or sucking air then sure. But you would probably see that show up as a dip in fuel pressure. Low fuel also raises the chance you suck something up and clog the system.
 

Crush 4

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If the fuel pump were weak and/or sucking air then sure. But you would probably see that show up as a dip in fuel pressure. Low fuel also raises the chance you suck something up and clog the system.
Ok makes sense. Btw thanks for continuing to answer my questions, I appreciate it!
 
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Maybe I mentioned this to you before, but a big aid to helping me figure out issues with my tbi is installing a wideband gauge. You van get them for less than 150 bucks.
 
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Crush 4

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