norcoastal

Very strange.

My car will run great then it will bog out like its either starving for gas or spark.

When I pull over it stalls.

It starts right up and I can rev it hi without problem, but then it has a rough idle, almosts pulsing.

If I run it at hi r's it seems to go away, but not always

It can go away for a week or more and then out of the blue it's rough again then stalls.

It's weird that it's not all the time.

If it's a vacuum leak or a ground, wouldn't it happen all the time?

GlenL

"If it seems like electrical, then it is."

Bad sensor or frayed wires. Maybe the fuel pump is going.

Mrmerlin

open the gas tank see if there is a whooshing noise

norcoastal

everybody a comedian :-P

Mrmerlin

Steve this is a serious request as the tank may be getting a constant vacuum and thus causing a fuel starvation issue

The valve that fails is just on top of the waterpump at the center of the V,
it can also cause the tank to impolode..

Also remove each vacuum line from both of the dampers and the FPR and smell the lines,
if you smell gas then that part is bad it leaks gas into the vacuum line and will cause the engine to run poorly

norcoastal

Great advice, THANK YOU. I'll check this weekend

AO

Also double check the Temp II sensor (the one with the blue conenctor on the water bridge next to the oil filler neck). I had put a little ground strap on there becasue the powder coating was preventing the water bridge/sensor from getting a good ground.

Mike Frye

Hey Steve,

Let me know your availability in the next few weeks. Maybe one Sunday afternoon (when the Giants aren't playing a day game ) you can bring your car over and we'll go through the whole test plan checking for proper voltages and resistances as well as checking for loose connections and bad grounds.

I'll see if I can borrow Adam's blink'r and we'll just go through it all soup to nuts. Shouldn't take more than 2-3 hours and if we still don't find it, then we'll post the results of our tests on this thread and see if anyone can help us out from there.

What do you say?

the flyin' scotsman

So its failing under load.

I'd upgrade the '87 brains to newer eproms with diag capabilities then with a JDS or Theo tester run all the tests.

Given all pass I'd them look at fuel pressure/fuel pump, the MAF and the LH brain. Hopefully there's a R'lister close that you can swap your MAF and LH.

AO

LH is a rebuilt. Dunno about the MAF.

Cosmo Kramer

Check all the grounds and make sure they are good clean and tight. There is one at the back of the engine that is important for the EFI. Also check the ground strap from the battery and the cable underneath that runs from the engine block to the frame on the PS. Would be good to take a look at the MAF wiring and the fuel pump like the others suggested.

norcoastal

Mike you're on. I would really appreciate that.

Sundays are rough with both Jets and Giants killing it. Any Chance you have a TV in your garage???

86'928S MeteorGrey

Hmmmmm.... Is this an auto? I sure hope not. TBF?

AO

It is an auto, but I have checked the crank end play and was dead on in spec. O.040mm IIRC. It is also fitted with a PKlamp as added measure.

And just in case you're thinking the other TBF, it has a new timing belt and Porkensioner.

My guess is that it's a grounding issue or a Temp II failure.

Be sure to check the Temp II values at the LH/EZK as this will rule out any harness issues.

86'928S MeteorGrey

whew... Glad to hear TBF has been ruled out. Those symptoms always make my heart jump up into my throat. If the above suggestions don't cure it (most of the bases are covered up there) you might check the under hood ignition modules... maybe running on 4? My S4 had a bad module that when it started running poorly (on 4) I could turn off the ignition, restart, then it would run fine. After a while of doing this it went to 4 all the time. I swapped out the modules one at a time and it corrected the problem. Good luck with the diagnostics.