sick SHO

[grimesland]

Hello group, I have a dilemma. Actually my 91 SHO MTX has the dilemma. I was driving it home from work stopped at the gas station and filled it up. "premium unleaded fuel only" LOL When I restarted it started it, it would barley pull it's self. I figured several cylinders shy. I continued to "limp" it home. After a mile or so. It just suddenly began running perfect again. For a day...
I wrote it off to a self fix. I love those... The next day It began again and went about 10 miles before it cleared. That was the last time I have had all 6. I did notice when it was running poorly the RPMs were 1/2 what they should be. For example at 60mph I normally read around 3,000. Now, with the problem I am only reading 1,500 at 60mph. With terrible fuel consumption no less. Idle normally around 1,200... now a very rough 600. If anyone has any ideas please shoot them my way. Thanks, Jeff

 

[Mr Anonymous]

You need to start by determining the current maintenance status of the car. Check the plugs and wires, specifically looking for oil in the plug wells. You'll also want to check the PCM for trouble codes that may point to other problems, there are links to sites with easy DIY instructions in my signature; all you need is a short piece of wire or a paper clip.

 

[the on going reality of shopower]

i had this twice on my 91 + and it was fuel injectors plugged up

 

[JSMCPN]

I had the EXACT same problem with a SHO I just bought. The tachometer gets it's RPM signal from the DIS, and if two cylinders are not firing (two cylinders fire each time as they share a coil) then your tach signal will only send 4/6th of the actual RPM which won't agree with the tach calibration. I bought my car in this condition knowing it was either the DIS, coilpack or ECU, in that order. On the way home from buying it the power would suddenly come back and the tach would jump up. Then it got real intermittant then went back to limp-mode for the rest of the trip.

Run KOER diagnostics as per SHOTimes.com and do the "goose" test, which is a cylinder balance test where it shuts down each injector one at a time and measures for similar RPM drop across all cylinders, then tells you which failed. If a cylinder is not firing at all, this test can usually identify it. I bet you anything the ECU will fail TWO cylinders, and when you look at the coil pack you will see that both those cylinders are fired from the same coil on the pack. There are 3 coils on the pack, each has two towers to connect plug wires to. Cylinders are numbered, standing in front of the car:
1, 2, 3
4, 5, 6
The coil pack is labelled:
5, 1
6, 2
4, 3
You should see one of those combinations of cylinder test failures. Mine failed 2 and 6.

Coil packs are much less likely to fail than a DIS module because they are located further from a heat source, have no moving parts (DIS has sensitive electronics), and are encased in epoxy. I also got appropriate fail codes from the ECU during diagnostics so I concluded it was the DIS module or wire harness. Borrowed a DIS, everything was right. Got one on eBay for $38 shipped

 

[projectSHO89]

In order of likelihood:

DIS module
Wire connectors/harness to coil pack
Coil pack

It will be one of these three items.

For previous discussions that may pertain to your situation, use the ADVANCE SEARCH tool, keywords "COIL TACH DIS" and my username. You will find, among other things, several threads that sound similar to what you are encountering.

Steve

 

[grimesland]

Thanks group

Installed DIS off 91 supercoupe. Ebay $20.00 Car runs perfect.