Stumbling and Studdering

[fast65]

So last Weds. my SVO started having an unusual problem. It was running perfectly fine for the first 15 minutes or so, then I got on the highway and all of a sudden it started to stumble, soon there after it just quit accelerating all together, the car didn't die, but the rpms just started dropping and giving it more or less gas didn't do anything. I was able to get it off the highway and restart it, but in another few minutes driving through town it started to stumble again, I let off the gas, then I went to give it a little more gas and it started to kind of jerk violently.

I really have no idea what it could be, I haven't been able to pull any codes, and someone mentioned that it might be the fuel pump, although I put a Walbro 255 in it about a year and a half ago. What do you guys think it could be? Thanks in advance.

[svobud]

If your fuel pressure is good, all hoses intact,etc ... I would look at the TFI.

[fast65]

I completely forgot about the TFI, I'll check that. Thanks!

[GAboySVO]

Since you have an 84, I would suspect wiring. Perform the wiggle test and see if you can track down the culprit. My guess is it is in the TPS or VAM harness.

[fast65]

Since you have an 84, I would suspect wiring. Perform the wiggle test and see if you can track down the culprit. My guess is it is in the TPS or VAM harness.

The wiggle test? Do I just let it idle and then start to wiggle the VAM harness and TPS?

[svono50]

Wiggle test...that is pretty much what you describe. You move around the various wires/harnesses to see if you can duplicate what you are seeing when driving. If you put the EEC into "wiggle test" mode it will record any error it sees as compared to when it is nomally running it will only capture certain errors once they have had enough occurances. Now I have to say I have yet to try out this mode of operation on the EEC, but it would seem that it would be an invaluable tool for us and our 'quirky' cars.

Based on the fact you seem to see the issue crop up after several minutes of driving leads me to think it could be something electronic as Bud mentioned with the TFI or the PIP or something in the dizzy. When parts start coming up to temp they expand and sometimes break electrical connections that are there when cold. Make sure your TFI has the proper thermally conductive grease on it otherwise it will overheat and cause issues similar to what you describe. Let us know what you find.

[fast65]

Wiggle test...that is pretty much what you describe. You move around the various wires/harnesses to see if you can duplicate what you are seeing when driving. If you put the EEC into "wiggle test" mode it will record any error it sees as compared to when it is nomally running it will only capture certain errors once they have had enough occurances. Now I have to say I have yet to try out this mode of operation on the EEC, but it would seem that it would be an invaluable tool for us and our 'quirky' cars.

Based on the fact you seem to see the issue crop up after several minutes of driving leads me to think it could be something electronic as Bud mentioned with the TFI or the PIP or something in the dizzy. When parts start coming up to temp they expand and sometimes break electrical connections that are there when cold. Make sure your TFI has the proper thermally conductive grease on it otherwise it will overheat and cause issues similar to what you describe. Let us know what you find.

I'll definitely let you guys know what I find, I certainly want to know what it is as I'm supposed to be moving for my internship on Friday :/ My brother thought it might be the inlet hose to the turbo, but I had that problem a few months ago and I ended up putting a piece of heating tubing inside of it to fix it. I'll replace the TFI and do the wiggle test, but do you guys think it could be anything involving the IAC since I took it off to clean it out the other day?

EDIT: For the life of me I can't remember what the PIP is, what is it?

[svono50]

Your IAC is pretty much closed at part throttle operations and only used for idle and I believe WOT, so I don't think it would have much to do with it.

I may sound like a broken record, but check the resistance on your ECT sensor in both cold and warmed up. It is located in the top/center of the lower intake. Unplug the connector and measure the resistance across its pins. If you don't see a change between the two readings, then it could be one of the potential culprits. As your EEC goes from cold startup mode to warm mode (those aren't the proper terminology) your EEC may think the engine is very cold or very hot and adjust your fuel delivery to where it won't run very smooth and seem like it is fighting itself.

[fast65]

Your IAC is pretty much closed at part throttle operations and only used for idle and I believe WOT, so I don't think it would have much to do with it.

I may sound like a broken record, but check the resistance on your ECT sensor in both cold and warmed up. It is located in the top/center of the lower intake. Unplug the connector and measure the resistance across its pins. If you don't see a change between the two readings, then it could be one of the potential culprits. As your EEC goes from cold startup mode to warm mode (those aren't the proper terminology) your EEC may think the engine is very cold or very hot and adjust your fuel delivery to where it won't run very smooth and seem like it is fighting itself.

Alright, I'll check that as well. I know it was having some troubles idling for the first 5 minutes or so this winter as well, so maybe that had something to do with it.

Oh, I just remembered as well, the weekend before all this started it would start bouncing at idle when I would come to a stop after driving on the highway. It kept bouncing from 250 to 750 and back, really weird.

[svobud]

The PIP (P-something Ignition Pickup) is located inside the distributor. It sends a signal to the TFI for something like a crank position.

[fast65]

Thanks Bud!

So my brother is actually working the car right now, he just told me that he did a wiggle test on the KOEO and it came back with a circuit fault. He's checking out the ECT right now.

[fast65]

Alright, we've got 4 codes: 66, 82, 83, 54

BTW, it has an LA3, I don't know if that makes a difference

[BrianO]

probably VAM... the 82 and 83 are normal for LA3's, other two are MAF and IAT..

[fast65]

So do I need to replace the VAM?

[BrianO]

I'd search for VAM, there's a test procedure someone posted with pictures a while back. could be faulty, could be wiring..who knows..