Ok, Ok, I think I have got it...

OK guys, I have spent the last 3 days searching before writing this, but I have not got a clear answer from anything I have read. (And I have read a lot!) Maybe no one knows that is why I am revisiting this subject. I have a 90 xj with 220,000 on the clock. This is what I have done recently (read last few weeks). New o2, cleaned valve cover and CCV and lines, new air filter and plug wires (good ones), new battery wires, cleaned the TB, new trans starting sensor thingy (can´t remember the name of it) and i checked all the bolts for compression leaks. I STILL have a rough idle after it has run for a while, I STILL have a very low idle around 3-400 (it will even stall sometimes with the AC on) and I STILL have hesitation first thing in the morning, plus my milage is in the toilet and power aint what it probably should be.

My friend hooked up his computer reader from Snap On and it said all the sensors were fine but it is running lean and the system either never closes or opens like he said it should (I can´t remember which) after it warms up. Sorry I am really try to learn everything I can here but I just can´t seem to keep up with what my Jeep throws at me...

So what next? Here is what I was thinking of doing and the order I was going to do it in.
Tell me if I am missing something or whatever...
1-TPS
2-EGR
3-MAP

I have read a lot about this stuff and it seems no one has really fixed this common problem has anyone got ANY idea what is REALLY going on? I hate to just keep replacing parts!!! Thanks in advance to everyone.
:repair:

If all the sensors are OK from the snapon tool, you checked them with a meter and they seem to function correctly I think I would revisit all the grounds and make sure you are getting a good ground. Just an Idea.

A good ground from where? All the individual sensor grounds?

saltilloxj said:

A good ground from where? All the individual sensor grounds?

Click to expand...

Start with the one on the rear driver's side of the head to the firewall. Then on the passanger side of the engine block behind the oil filter there are a bunch of wires going to a bolt. Then run a good size wire from the battery minus post to the body. Have you cleaned the throttlebody and idel motor thingy whatever they call it? If not use carb cleaner and a tooth brus.

JoBo

C'mon guys somebody has to have some more information?!?!?

How is your fuel pressure?

ditto on fuel pressure. Should be 31 psi at idle and 39 with vac line removed from fuel pressure reg.

Dave

Check your TPS adjustment.

You used the terms "closed" and "open." What your friend must have said is that it isn't switching from open loop mode (warm up mode, in which the sensors are ignored and the ECU uses a pre-set fuel curve) to closed loop mode (where the ECU changes the mixture according to data from the sensors). This is a function of the ECU and the O2 sensor, and mucking around with the EGR, TPS or fuel pressure regulator will not help any.

I can't imagine why it shows running lean, because the open loop mode is set to run rich for warm up. Ask your friend if he meant it's not going into open loop mode when cold. If that's the case, it isn't the O2 sensor so that means you're looking for an ECU.

Will any ECU work or must it be from a 90? Thanks also for al the help... I will check fuel pressure later tonight.