Intermittent Miss - 92 3.0 Van

[cobra2411]

Had a 92 Van in the shop last night, 165k miles, rebuilt heads (10k) 3.0 v6, auto.

It was in three weeks ago for a bad cat, if you tap it, you can hear the innards were all broken up.

It was back for state inspection and the owner complained of an occasional miss. It took a while, but we were able to recreate the problem. It seemed to do it more in reverse for some reason.

Anyway, in reverse I brake torqued it and hit the gas. It would start to stumble and cough. At the same time I had the scanner hooked up and noticed a couple things. The fuel trim was -22, but the 02 volts where 0.02. It was like this the entire time it was stumbling, then you would see the trim go positive, the stumble would clear up and the 02 rose to .88v

TPS was steady 50%, temp was steady 204, Stall RPM was 2200-2300, but while it was stumbling it was only able to hold 1400-1500. Manifold vacuum was about 1.7hg while stumbling and about 4-5hg at stall normally according to the computer.

02 sensor is brand new and the problem was observed with both the old and new sensor. Fuel pump is also new, but I didn't get pressure readings during the test.


What would cause the computer to pull fuel when the 02 is showing dead lean?

Thanks,
David

[turbovanman²]

I would verify fuel pressure and volume before you go any further.

Were new plugs, good wires installed at the time of the head job?

Try wiggling the wiring harness when it does it.

[Big_P]

How do the plugs look? Check 'em all...make sure the wires are all good.

[RoadWarrior222]

I have some wierd stuff going on with mine lately, and I'm noticing it reacts more obviously to different brands of fuel than it used to. Anyhoo, when I get a day that's not so windy it's gonna tear the hood off, I'm gonna start investigating the FPR on mine. On that one I'd be thinking the IAC or MAP would need looking at, and vacuum issues investigated first. Could also be a grounding issue somewhere if it does it worse in reverse it could be the strain on a contact point is different.

Also look out for the crankshaft woodruff key being broken on the crank pulley, sets the timing jumping about. If you hit it with a timing light with the CTS disconnected and the mark jumps all over the place, it's broke or bent.