91 5.7 TBI runs very rich - 1227747 $42

Hello,

I have 91 Vandura with 5.7 TBI which I bought with engine damage. One valve was partially burned and it did not run well.

I removed heads, fixed the problem, had the heads machined and did all of the usual stuff. The engine does not run well since. It is possibly even worse than before :-/

It idles very rough, sometimes it idles around 700 rpms, then in goes to 1300 rpms, it often suddenly dies. I thought it would be some sort of electrical issue, so I bought ALDL-USB cable from eBay. I have just recently received it and figured out a way how to connect it to tunerpro rt. It seems that there is no issue I can see right away, except for the vacuum changing rapidly.

What does the "open loop" mean?

Is there a way I can alter the ECU program? Well I know there is, but I am not sure whether I need a special cable or if the one I have will do. I believe that the engine would run much better if I managed a way how to inject less gasoline during idle.

There is a log file included, if someone is able to read something out of it, I would be grateful.

Thank you,
Ravex - Czech republic, EU

P.S.: I was depressing the accel pedal when recording this log file. I believe it can be seen from TPS.

The only way I found so far to make it run pretty much okay was to put about 320 ohm resistor instead of temp sensor. It was not so rich, there was much less of unburnt gas odour from the exhaust.

"open loop" means that the computer is not using feedback from the o2 sensor to adjust the afr.

As for what hardware you need, head over to moates.net to do some reading and shopping.

Ravex. I would verify all sensor grounds are attached and making good, clean contact with the mating surface. Often times durning engine repair, these grounds get disturbed, broken, etc. I believe you should have 2 separate ground wires which attach to the thermostat housing, make sure both are there and in good shape. I havent had a chance to look at your Log file yet, but you mentioned the coolant temp sensor, it is common for them to fail and cause an overly rich(too much fuel) condition.

Buddrow

Quote:

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Originally Posted by ravex

It is possibly even worse than before :-/

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Me:

I would first confirm that there are no vacuum leaks on the top end, being that is was just reassembled.
Then move on to step 2, a compression test, then go after fuel, ignition etc.........

And, make SURE you have a GOOD ground for the pcm .

double post :rolleye: