My '90 2.9l suddenly developed an engine miss and will not idle. This happened after the truck was idling for about an hour - was winching tree stumps out and wanted to keep battery charged. I have a mechanical temp guage and I continuously monitor temps - always in the 190 area so it did not overheat. After cooling off it will not start. It has run just fine up to now. Could this be an O2 sensor or do I need to get a code reader? Any ideas??

 

i would pull the codes and hopefully that will tell you something

 

Note that you can pull codes with nothing more than a paper clip. Read Ken00's tech article on pulling EEC-IV codes.

 

Tried starting it today, started and runs rough, misses, still dies at idle. Bought a code reader, plugged in according to instructions, turned on ignition and cannot get the reader to "talk" to the computer so can't download codes. Anyone have a similar situation? What are the chances the diagnostic plug is bad? I suppose it could be the code reader, don't have an analog voltmeter for the "manual" test.

 

have you checked your fuel pressure at the fuel rail? when was the last time it was tuned up? such as plugs,wires etc...have you checked all your wiring connections at the tps switch and iac control valve? it sounds like you have a fuel related issue

 

The problem could well be one of your suggestions, but why can't I pull codes, at least an 11 or whatever the all clear code # is? Also due to the extended idling and under hood heat I was suspecting the TIF module. I was trying to eliminate electrical issues via the code reader as fast troubleshooting then if all ok look to the fuel system.

 

what kind of code reader did you get? does it plug right into the main connector under the hood {not sure of exact location on the 90} did you try doing a koeo test?

 

The code reader is an Innova Equus #3145 for Ford 1981-1995 models and plugs directly into the diagnostic plug located on the inner fenderwell on my '90. Supposed to plug it in, turn on, turn key on and then press the test button which is supposed to tell the computer to self test and then download codes. Pretty simple, but doesn't work. Tried several times. Code reader batteries good (new) and I did test them with voltmeter. Code reader shows 000 on screen as per directions but nothing happens when test button is pushed. I thought this would be an easy way to get the "check engine" light problem resolved.

 

I've never used that (or any other) code reader. I've always used a paper clip (or other jumper wire) and a voltmeter to get codes. The first piece of advice I can give is to try pulling codes using this latter method to make sure the code reader isn't the problem. If you still get no response from the computer, start checking for power to the computer, the computer's grounds, and the wiring between the self-test connector and the computer.

Just read the bit about you not having a voltmeter. The voltmeter I use to pull codes cost me ~$3. You should be able to go to Wal-mart, K-mart, Harbor Freight, or similar and buy the cheapest analog voltmeter you can find. Even a cheap test light would work.

 

i'm not sure how the computer works on the 90,i scanned my 86 a while back and had no problems to get to scan..have you looked at ken00's troubleshooting guide at the top of this forum?

 

I do not have an analog vm, only a digital. But I did try the test light method, steady glow if that means anything. I'll try to pick up an analog today.

 

Also pulled the spark plugs - are very sooty. So, for whatever reason is running very rich which is what I remember smelling fuel when the miss happened. Checked the FPR and is ok, I had replaced this last year. Still can't get it to throw any codes, and now it won't start - this seems to be intermittant as it did start yesterday. Driving me nuts. Think I'll throw in a TFI just to eliminate. Like I said, I thought I'd start with the easy troubleshooting - codes - and then go from there. Can't seem to even get there.

 

Did you hook up both the large and small (single-wire) connectors to the reader???

 

Yes, both connectors hooked up to reader. So far here is what I've found.
1. Still can't get any codes.
2. Replaced fuel filter.
3. Checked fuel pressure - runs to 40psi per specs but very slow to arrive.
4. Fuel pump runs continuously - even when engine not running. What turns the pump off after reaching and holding pressure?
5. Spark plugs very sooty.
6. Removed and cleaned out O2 sensor - very sooty.
7. Could this be a weak fuel pump or leaking injector?
8. Check engine light is still on.
9. Would a lack of fuel (pressure) cause it to run so rich?
10. Tried starting today but didn't take right off so I quit grinding the battery down.
Time to trade for another jeep?

 

1. Is the wiring between the self-test connector and the computer good? Have you checked for power/ground to the computer?
4. Computer is supposed to turn the pump on when the key is turned on. After a couple of seconds, if the computer doesn't see a PIP/TACH signal, it should turn the pump off. Has someone bypassed the fuel pump relay (passenger fender under hood. see wiring diagram)? Relay sticking closed? BTW, pressure is controlled by a mechanical back pressure regulator on the fuel rail. Excess fuel is returned to the tank. Any sign of fuel in the vacuum line to the fuel pressure regulator (gas in line = bad FPR)?
7. A leaking injector? maybe. A leaking FPR? more likely. A weak pump? Does the fuel pressure stay at 40 psi while starting/trying to start the engine? If so, then the pump is probably ok. If the pressure drops off, then, maybe.
8. Can't do anything about this until we figure out why you can't get codes.
9. Low fuel pressure would cause it to run lean, not rich. When you get a chance, see if the fuel pressure is dropping off or holding steady when you start/try to start the engine.
Time to trade for another Jeep? Uh...well...no...maybe...if...no comment.