Running rough/engine light/cant read codes??

[myvmax1]

92 8V TBI 5 speed, aprox. 140K on the clock


Truck is my daily driver to work, havent really noticed anything out of the ordinary. Installed new plugs, wires, cap, rotor, air filter, etc. about a month ago, didnt seem to change much just wanted to tune up before winter.

Today:

Drove to lodge, shut the truck off. It was off probably 15 minutes. Start it back up and it takes alot of cranking then fires, running VERY rough and will only stay running if I apply the throttle. No throttle input and it drops to Harley Davidson idle and dies. Has deffinitly lost power as I had to drive it home in this state. Check engine light is on, but I cannot get the codes to read. Jumped the connecter (under the hood near batt.) like the manual says but the light dosent flash, just stays lit. Took the plug apart and connected prongs directly, same story.

When I bought the truck it didnt run and I had to send the ECM to the guy reccomended here on the forums for fixing. Worked like a charm, but is it possible that I lost the diagnostic function in that?

I cranked the IAC way up so it would idle (its WAY up, can hear it sucking through the hose) so I could look at it and spray some TB cleaner in the TB and the vaccume hoses, No change here either.

Any ideas anyone?

[Bex]

If the CEL is on with the key on and on when running and you cannot get codes, it is possible that the nag function is on (which would go on normally at an even mileage, like 140,000, etc). Not quite sure where the nag switch is in your car - you should have a small panel under the steering column which can be removed - the nag is either just beneath that panel opening, or else toward the driver side front speaker. You probably will not be able to see the switch, just feel for a tiny sliding switch. Wherever the switch is now, push it in the opposite direction to turn the nag function off. Once this is done, try to jump your codes again.

Suggestions: Put the IAC back where it was. Idle is a symptom of a problem, not the problem itself. This can be anything from the timing belt having jumped, to bad gas, etc. When the car is cranking and hard to start, have you checked the plugs to see if the car is flooding? (or tried the 'unflood mode' with gas pedal floored when trying to start the car?) Conversely, also try to start with the gas pedal down about 10%, which adds air to start up. Will the car start easily with test fuel?
You may want to check the timing belt and/or do a compression test to verify that the car is timed/tuned properly

[myvmax1]

Ok, going to look for this nag switch now.

I know the idle is the symptom, only turned it up so that it would idle without me having to hold the throttle (dont have a helper).

Will check the plugs, timing and compression. Forgot to mention that I changed the timing belt, lashed the valves, and set the timing back durring the summer. So i have my doubts but will do anyway. I have detailed reccords of all this if exact mileage becomes an issue.

Forgot to mention earlier, the tach jumps intermitantly, like a voltage spike along with the rough idle.

[myvmax1]

Found a pretty serious problem.

Pulled the plugs and they are a matte, sooty, black. I wouldent have expected this as new as they are, but I wonder how much of that is from todays 20 minute drive while running like crap or the cleaner I sprayed in to try and "clear up" the miss, it did make it smoke. Cyl 3 has the black, but is oily. Unlike the others.

Compression test: All plugs out, ignition disconected, accelerator floored, cranked till the needle leveled off.

Cyl 1, 2, 4, low of 150 high of 160 psi

Cyl 3, 30 psi NOT GOOD

When testing the others I could hear that cylinder hitting the tester, building pressure. On cyl 3 it just sounded like an electric drill, starter spinning.

Since it ran ok to the lodge, then failed on restart, am I to assume it is the valves in that cylinder?

EDIT: Now that I think about it, it hasnt started smoking (any more than normal lol) so I wouldent think it would be the rings. Sounds like valves, good news is I have two complete engines for spare.

[myvmax1]

Found what I believe to be this "nag" switch, under the dash driver side mounted kind of beside the speaker. Tried it both ways and still cant read codes. I use the same plug that you jump to check timing right? just different holes in it (2and3).

What is the purpose of this switch anyway?

[aquanaut20]

The switch is to NAG when critical service intervals have been reached, NAG! NAG!

I would do a leak down on the bad cylinder to confirm condition.... also check the lash and condition of lock nuts..... Philip

[Bex]

Philip's post x2.
Actually, your compression values (on the good cylinders) are still a bit below normal - my 1991 gives at least 170 on all cylinders (but it's a *magic* car anyway....). Do your compression test again, using a tablespoon of oil in the #3 cylinder and see if the compression value comes up (rings). If not, check the valve for #3 (should check them all, anyway, due to your compression values).
Regarding the nag, you are saying that you push switch one way - can't get codes. Then push switch the other way, and still can't get codes, yes? Light stays on no matter which direction switch is. And you are jumping codes according to correct pins:
Check Engine Light
You may want to try removing the fuse for the dome light for a minute, then replacing. This will reset the ECU, then try to get codes again with nag switch on one side or the other.

[myvmax1]

Yes that is the procedure I have been using for code check. I'm going to start at the top and work down today. Pull the cover and check all components and adjustment, then the head to inspect head gasket and cylinders.

150 psi did seem a bit low to me, in comparison to what I'm used to working on, but I didnt know for sure given these engines mild output.

Thanks for staying with me on this,

[xxx]

#3 is DOA ( 150 is par for any 8v cold for sure !) forget them, deal the dead #3
its not a 16v, at all. its a 8v.
what's CEL got to do with 1 dead cyl?

you failed test 1
bad motor
bad spark
bad fueling

you failed #1 , its a no brainer.

some posters have never overhaul a 8v , nor tired hot and cold compression on one, that they rebuilt themselves ,then speculate.
i get 155 (72f) and 150 is inside the range of, gauge accuracy and actual cold temps that can be, anything.

[Bex]

Whatever. Do the wet test on cylinder #3 and see if you can get the compression to rise. If not, check the valve lash. Good luck!