TBI Issues

[RoryH19]

I think my TBI 350 is going south.
Every now and then it would ruff idle and have the surge in power when cold.
Now I've noticed at certain times in WOT it will back fire and pop, lose power. Has never done this before.

I replaced the fuel filter on the rail and did see minor contaminants but nothing major.
Ran it for a week and still the same issue. Haven't found any vacuum leaks yet.
Everything seems to work. Goes into overdrive, cruise control works, AC vent doors work...

I rebuilt the TBI around 4 years ago, could it need another rebuild?
Could the fuel pressure regulator be the issue?
I've thought about an aftermarket one that is adjustable.

Thoughts?

Thanks.

 

[CSFJ]

Have you checked fuel pressure yet?

 

[RoryH19]

Assume you mean pressure past the regulator in the TBI itself?
If so, not yet.
If you mean fuel pumps, I have dual tanks and it does it on either one.

 

[CSFJ]

Assume you mean pressure past the regulator in the TBI itself?
If so, not yet.
If you mean fuel pumps, I have dual tanks and it does it on either one.

Yeah, I was thinking pump pressure when I asked. Didn't realize you had twin tanks. When you mentioned a slight difference after replacing the pump, that's what got me thinking a fuel delivery issue.

 

[RoryH19]

Yeah, I thought pump at first too. That's why I tested with both tanks.

 

[CSFJ]

@1987 GMC Jimmy is probably one of the more knowledgeable people about the tbi systems on here. The few tbi's I've had over the years never gave me reason to get too in depth with them.

 

[1987 GMC Jimmy]

If no SES light, you’re in for a treat. I’d check your injector spray pattern, and you can also test the resistance on the injectors. Should be around 1.3 ohms low side depending on your DVM. If nothing’s fishy there, I’d be suspicious of a TPS dead spot near WOT. Getting some live data on TunerProRT might help put things into perspective. At least on the sensor data. With ignition, the distributor can do weird things when there’s a problem. Make sure it’s not full of rust, your cap and rotor aren’t oxidized, melted, cracked, etc., and you can test your ignition coil, pickup coil, and ignition control module. This’ll cover a lot of bases. I’d make sure you don’t have any vacuum leaks whatsoever including brake booster or even a trans modulator if you don’t have a 700R4 or a manual. Oh, and you can try capping the EGR valve off to see if that’s causing your WOT problems.

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[RoryH19]

If no SES light, you’re in for a treat. I’d check your injector spray pattern, and you can also test the resistance on the injectors. Should be around 1.3 ohms low side depending on your DVM. If nothing’s fishy there, I’d be suspicious of a TPS dead spot near WOT. Getting some live data on TunerProRT might help put things into perspective. At least on the sensor data. With ignition, the distributor can do weird things when there’s a problem. Make sure it’s not full of rust, your cap and rotor aren’t oxidized, melted, cracked, etc., and you can test your ignition coil, pickup coil, and ignition control module. This’ll cover a lot of bases. I’d make sure you don’t have any vacuum leaks whatsoever including brake booster or even a trans modulator if you don’t have a 700R4 or a manual. Oh, and you can try capping the EGR valve off to see if that’s causing your WOT problems.

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Thanks for the feedback.
No SES on.
Distributor, cap, rotor, module, plugs and wires all replaced around 4 years ago.
EGR replaced 3 years ago.
Of course they don't last forever.

I'll try TPS and vacuum leak.
Good idea on the trans module. I've noticed every now and then it has a hiccup in overdrive.

 

[dvdswan]

Really don't know much about TBIs but I thought that backfire/pops were more ignition related.

 

[RoryH19]

It's possible and for sure on carbureted engines ignition issues (eg bad timing) will cause backfires.
It's an intermittent problem which will take some time to find.

 

[1987 GMC Jimmy]

If you have a 700R4, then no modulator. If you have an aluminum cap/rotor with around 30 or so thousand miles, it might be time for a new one. Also, don’t discount the pickup coil and ignition module. The tests are quick and easy.

 

[RoryH19]

Yes, 700r4.
I'll check the ignition parts. Probably close to 30k on those parts now.

 

[1987 GMC Jimmy]

Yes, 700r4.
I'll check the ignition parts. Probably close to 30k on those parts now.

If you have a brass cap and rotor, you’re probably in better shape, but I did the AC Delco parts, which are aluminum, and I limped to 30K, but it was running so bad, I just got a Duralast cap and rotor set which were brass and had a limited. lifetime warranty. No issues.

 

[RoryH19]

If you have a brass cap and rotor, you’re probably in better shape, but I did the AC Delco parts, which are aluminum, and I limped to 30K, but it was running so bad, I just got a Duralast cap and rotor set which were brass and had a limited. lifetime warranty. No issues.

That's what I have. I bought the entire duralast distributor with a cap and rotor as one kit. I'm sure the coil is also duralast. Plugs and wires are bosch

 

[RoryH19]

I'll take a look under the cap to see if I notice anything. Along with wires, plugs, coil...
Problem is that most of the time it runs fine, then it wants to surge, or backfire. Really hard to nail down.