Rough idle, missing, and no power.

[isusho]

First I have searched but have tried things that I have found and need another opinion.

One day when driving down the road my SHO (92 MTX) started to hiccup (best word I can think of) like it was running out of gas. When I got home pulling into the driveway it sounded like it was intermittently missing. It has no power but the missing seems to go away, or just sounds that way, after 3k.

Since it started acting up I tested the fuel pressure (30 psi at idle, 40 at WOT), thought that was a bit low but the pump and filter are almost brand new and not making any noise. I then checked the spark plugs and found oil in one plug well, so I replaced all the plugs and the valve cover gasket. I checked the MAF and the sensor was clean and when I disconnected it and the car runs worse. I checked the plugs and all but the one that was at 4k the one that had oil on it tested at about 7k. Ran codes and got none from the computer

I’m thinking DIS, coil, wires, or maybe computer. Any good ways of testing these individually? Anything I’m forgetting to check? I doubt it is crank cancer but I will be checking for that when I do the crank seal later this week.

 

[SHOtimer]

I would check the ground path on the intake, did the strap from the intake to the firewall break? I would also check the timing belt, is it still tight?

Doug

 

[zanzimaru]

you might want to look into your iac or into a possible vacuum leak... to check iac you can do as you did with the maf (unplug while idling)

 

[isusho]

The ground strap is tight. Checked it while I was pulling the intake. Would the iac effect the car when you are going down the road?

 

[SHOtimer]

Yes, if it was really messed up.

Have you pulled the upper timing cover to make sure the timing belt is ok?

Doug

 

[isusho]

Not yet, might have to do that before work. I checked all the vacuum lines but I'll double check them might have missed it. Thanks for the help so far.

 

[shobote]

Sounds like symptoms of a dirty MAF filament IMO; mine did the same thing; bucking or hiccupiing of power. If you are running an oiled air filter, this is more than likely the cause (oil contamination on the AMF filament) I would clean the MAF filament and see if that solves it.

 

[isusho]

I'm running a regular filter so it's not oil contamination. I'll try cleaning it tomorrow while I'm doing some other stuff on the other side of the engine.

 

[shocar]

just had to replace my DIS on my 92mtx, symptoms, rough , missing, 1000 rpm-3000 rpm ran ok at higher RPMs. I replaced the plug wires, fuel pump and fuel filter and it still had the same the problem until I switch out the DIS ---- that fix the problem.

 

[isusho]

Any ways to test the DIS without replacing it? I'm checking the timing belt tomorrow when I replace the main seal. It started leaking a little bit.

 

[isusho]

So I opened up the front of the engine and found the timing belt had skipped a tooth on both cams and the crank. Interesting yes but did not fix the issue. Changed the main seal and the timing tensioner for good measure.

Next I'm going to check the injectors and wires again.

Edit: Cleaned MAF and got DIS tested. DIS is ok MAF cleaning did nothing to help.

 

[isusho]

UPDATE:

Now without constant gas it dies almost immediately. Tomorrow I'm checking fuel pressure again and probably take the DIS into Oreilly's again for a test. Also going to run codes again to see if anything is throwing a code now that it dies.

Anyone have an more suggestions on what it could be? And thanks for all the help so far.