7.4 tbi timing issue

[Hartwell]

my ‘94 7.4L tbi burb has been running real rough lately. It misfires/shudders badly and won’t accelerate quick at all. So far I’ve replaced the plugs, wires, cap, rotor, pcv valve and fuel filter and it hasn’t solved anything. I checked the vacuum lines and they’re all good. When I went to adjust the timing, I’d unplug the computer under the dash where the glove box is, set it to 4 degrees top dead center and then I’d go to plug the computer back in and it shoots up to 10 degrees and still shudders and misfires. I’m taking it to the shop tomorrow to see if they can offer some insight, but I’m totally lost on this one. SOS gmt400 community!!


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[Hartwell]

I’m also getting a ticking/clicking sound from my distributor cap. It’s not a constant click but almost rhythmic


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[LC2NLS6]

I'd check fuel pressure. Could be a bad fuel pump, enough fuel to start and run but not well. One of mine (93 burb) I just bought ran poorly, changed all that and then checked fuel pressure, swapped it out with a vortec one from a '96 and runs perfect now and FP is in spec.

 

[Schurkey]

^^^ Yup, check fuel pressure.

Connect a REAL scan tool, look at the data stream.

"Clicking" in the distributor could be a spark misfiring inside the cap. Could also be rotor-cap alignment problems.

As long as you're dicking with the distributor, connect a spark tester to the coil wire after you pull the coil wire out of the distributor cap. See if the spark will jump an appropriately-large gap. (I use an HEI-style spark tester like the one below)

https://www.amazon.com/OTC-6589-Ele...+spark+tester&qid=1562866854&s=gateway&sr=8-2

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[Hartwell]

I'd check fuel pressure. Could be a bad fuel pump, enough fuel to start and run but not well. One of mine (93 burb) I just bought ran poorly, changed all that and then checked fuel pressure, swapped it out with a vortec one from a '96 and runs perfect now and FP is in spec.

Sounds like a good idea- about to head to the parts store to rent a fuel pressure gauge. Am I right in assuming there are no ports in the fuel system in these trucks and you just have to tap in where the filter is? Could the regulator also be the culprit?


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[Hartwell]

^^^ Yup, check fuel pressure.

Connect a REAL scan tool, look at the data stream.

"Clicking" in the distributor could be a spark misfiring inside the cap. Could also be rotor-cap alignment problems.

As long as you're dicking with the distributor, connect a spark tester to the coil wire after you pull the coil wire out of the distributor cap. See if the spark will jump an appropriately-large gap. (I use an HEI-style spark tester like the one below)

https://www.amazon.com/OTC-6589-Ele...+spark+tester&qid=1562866854&s=gateway&sr=8-2

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Would it be possible to just connect a timing light to the wire and just see if the light flashes? Because it only flashes when a spark goes down the wire, yes?
thanks.


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[bob850]

Just wondering if you ever found the cause of this. I'm having a similar issue with my '93 7.4 TBI Burb

 

[MIHELA]

Did you check the pickup coil in the distributor?

 

[Schurkey]

Am I right in assuming there are no ports in the fuel system in these trucks

Yes.

and you just have to tap in where the filter is? Could the regulator also be the culprit?

Two adapters that I have, one goes in place of the filter, the other screws to the fuel inlet at the throttle body. I use whichever one is easiest at the time.

A bad regulator would likely leak fuel.

Would it be possible to just connect a timing light to the wire and just see if the light flashes? Because it only flashes when a spark goes down the wire, yes?

Maybe. You'd have no idea if the spark was weak, though. I don't know how sensitive your timing light is. And if it didn't flash, it could be because the plug is fouled, not because there's a fault in the coil or cap/rotor/wire.

Using the timing light would be better than nothing. Buy the calibrated spark tester anyway.