HELP - 97 New rebuild, stumbles when I give it gas (1 Viewer)

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Sep 28, 2014
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Welp, I guess I got ahead of myself. After chasing my tail all day, I tried jumping the fuel pump relay again and the problem persisted. Back at square 1.
I did notice that even though all terminals on the TPS tested within spec, the VTA pin tested on the very low end when throttle was fully open.

Cleaned the MAF. Marginal improvement but problem persists.

It really does feel like it happens in a very specific point in the pedal position, and it is very consistent.
 
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Decided to monitor the timing advance and the ecu was advancing to 40 degrees just before the stumbling! Can that be right?
 
Joined
Nov 13, 2010
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Wish I could help, but giving you a bump is the best I got. The only thing I could think of is maybe the fuel lines or injectors got plugged up by some remnants in the fuel tank but I am no mechanic. Hang in there and hopefully it will get solved.
 
Joined
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Messages
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Wish I could help, but giving you a bump is the best I got. The only thing I could think of is maybe the fuel lines or injectors got plugged up by some remnants in the fuel tank but I am no mechanic. Hang in there and hopefully it will get solved.
Hey that’ll help! Found a couple threads with the exact same problem that resulted in them giving up.
 
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Posting to keep track of things I've tried as it is starting to get fuzzy.

Took of throttle body, cleaned all ports, readjusted TPS properly with feeler gauges. The stop screw is really hard to get to in the truck. TPS is perfectly adjusted now, but reads low on VTA with WOT.

Put timing light on igniter wire in to rule out failing igniter. Igniter continued to fire through the stall.

Have a new O2 sensor coming, and a cheap TPS that I will try to swap in to see if it helps.

Going to spend some time checking continuity of connections at the ECU tonight (bleh).
 
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Update: I put a new O2 sensor in. No luck...

I did notice that the fuel pump changed it's sound at the moment the engine stalls. I tried pinching the fuel return line to increase pressure. No change.

Exhaust also smells rich after a few minutes of testing.

Happens when fuel system is in open loop and in closed loop.
 
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Olathe, KS, USA
 
Update: I put a new O2 sensor in. No luck...

I did notice that the fuel pump changed it's sound at the moment the engine stalls. I tried pinching the fuel return line to increase pressure. No change.

Exhaust also smells rich after a few minutes of testing.

Happens when fuel system is in open loop and in closed loop.
Have you confirmed the temp sensor since that is what triggers a change from open to closed loop.
 
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Have you confirmed the temp sensor since that is what triggers a change from open to closed loop.
I’ve observed it in my obd2 app and it seems to be working properly. FuelSystem status switches from open to closed loop after warming up for a minute or so.

I still haven’t tested fuel pressure. I don’t think that’s the issue but going to try to get a tester and check it to confirm.

Trying to think through everything I did when I was rebuilding and one thing that comes to mind is I soaked the distributor to degrease it. Thinking maybe the hall effect sensors got screwed up, but I don’t have an oscope to test.
 
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Back at it again tonight. Got a fuel pressure tester but I can’t figure out how to get to the banjo in the back of the engine so I decided to put that off until later. Decided to pull the spark plugs to check them out. TheseAre brand new ngk plugs and I didn’t adjust any of them when I put them in, but did check the gap and they were pretty much spot on if only a little tight. I widened a few of them and reinstalled them. Surprisingly, it improved the problem! Still not great but definitely had an effect.
That combined with the rich smell seems to confirm it’s an ignition related problem.

for the plug whispered out there, here are plugs 5 to 1 (I didn’t touch 6 because it’s a bastard).

40B77C9E-9DC6-4404-A88A-7E842F3665C1.jpeg

1EF9BA36-AA16-417B-A056-891F6ACBD343.jpeg

6E5F8EC5-CACD-435D-BB79-0F0E4766BC3D.jpeg

C3997930-C5EF-4096-9F8D-45B52AEFF6E3.jpeg

E3E37E7A-E6DE-41AF-A85E-087F9B4EEB10.jpeg
 
Joined
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Plugs 1, 3, 5 seem to be firing and burning nicely.

Plugs 2, 4 are having issues. 2 may be burning a bit of oil but 4 doesn't look like it's firing at all. Check body of plug for cracks. Test the plug in the wire, on the manifold to check for spark while cranking.
 
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IT WAS THE FUEL FILTER!!!


Brand new, but must have gotten clogged from the junk in the tank. Also, if any one know the name and address of the guy who decided to put the fuel filter where they did, please let me know so I can burn his house down.
 

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