Last attempt to fix this myself...

[Cole94]

I've had a few threads on this.

It's a 94 Explorer XLT 4.0 4x4, 4 door.

O2 sensors are reading 0 at idle possibly indicating a lean condition. The engine is surging at a lot idle and a just a little when under 2000 rpms. It seems weak until it is warm, and it has hard warm starts. Several emmisions systems are spitting codes indicating undervoltage.

So, what on the engine helps the pcm control mixture? I have a code reader with live data feed so I think I can tell if some parts are bad or not. Ect seems fine, as well as MAF and TPS. What else should I look into?

Any help is greatly appreciated.

 

[shucker1]

PCM reads data from O2 Sensors (Upstream & Downstream) TPS, MAF, EGR Flow, Coolant Temp and Barometric Pressure along with a host of others and regulates fuel injector pulse duration to control mixture.

 

[Cole94]

OK thank you. This one just has the upstream O2's I guess I have a lot of testing ahead of me. Where can I find a list of this "host" of other sensors?

 

[shucker1]

Trying to find the write up.

It was done by another member a long time ago.

Basically it explains how it all works together.

 

[shucker1]

Look at the second tab from the left on the top bar.

"How To Threads"

There is a lot of information in there.

 

[Cole94]

Ok cool. Thank you.
I really hope I can fix it, there are no other mechanics in Topeka that I know of other than the dealership. I have yet to ask the guys at the local Orielleys.

 

[shucker1]

We will try our best to get you through it.

Have you checked the IAC (Idle Air Control) motor to see if it might be sticking?

 

[Cole94]

I remember checking voltages from it, it seemed ok.
When I start it , the rpms hover at ~1250 then drom to about 6-700 after a few minuted. I took that to mean it was working.

 

[410Fortune]

Can you tell us the codes you are getting? Low voltage codes?
You say the 02 sensors are reading 0 at idle and a possible lean condition

If you have a lean condition code this usually means that the computer has increased the amount of fuel being delivered by the injectors as much as it can and the mixture at the 02 sensors is still reading lean
This could just be low fuel pressure
It can also be intake leaks

If you pull codes from the ECM please post the actual codes here!

A surging idle, hard hot start, and lean codes usually have something to do with a weak fuel pump or bad regualtor
Have you checked fuel pressure at the rail?
Any loss of coolant?

 

[shucker1]

As mentioned above it might be best to make sure your mechanically sound first.

Check for cracked, brittle or broken lines that could cause a vacuum leak.

 

[FR-425]

O2's will always show 0 when in open loop. i.e. cold start. Heater circuit is probably open. No circuit codes available in OBD 1
You most likely have a wiring issue. Burnt by the exhaust for example.

 

[RustyMacintosh]

Ok cool. Thank you.
I really hope I can fix it, there are no other mechanics in Topeka that I know of other than the dealership. I have yet to ask the guys at the local Orielleys.

You get it to Pratt or Liberal I know several decent Ex guys who know the 4.0 well.

 

[Cole94]

I have gone through the vacuum system. There is now no leaks. Cruise control even works now.

It could be a lean condition, or rich, but no codes for such. I forgot to mention that it is getting about 11mpg. (Probably running rich, the exaust is rank) About 200 miles on a full tank. Going to liberal might be a little costly.

I just replaced the pump and the pressure at the rail tested good. I will try to get the codes for yall.
I will have to do this project over a period of about a month due to low income. I really appreciate all the help.

 

[RustyMacintosh]

I have gone through the vacuum system. There is now no leaks. Cruise control even works now.

It could be a lean condition, or rich, but no codes for such. I forgot to mention that it is getting about 11mpg. (Probably running rich, the exaust is rank) About 200 miles on a full tank. Going to liberal might be a little costly.

I just replaced the pump and the pressure at the rail tested good. I will try to get the codes for yall.
I will have to do this project over a period of about a month due to low income. I really appreciate all the help.

this forum has saved my ass several times
even when I pissed someone off in the 96-01 section by my limited--on-the-fly answer using a smartphone, I have learned more here than in law school ever could imagine

 

[Turdle]

Take the ECM out of the truck, open it and look for evidence of bad capacitors.

 

[Turdle]

Updates?

 

[Cole94]

Sorry for this taking so long. I just did this this evening

I haven't looked at the ecm. How hard is it to get to?

I pulled a plug.
Not bad. It looks fine. (Pic at end of post)

Mileage just jumped back up. I got 200 miles on 3/4 tank. I will do the math next time I fill up

Codes are
327: EGR below minimum voltage
543: fuel pump secondary ckt open PCM to Batt
I don't know what happened to the others. There was 7.

I hopefully will be replacing the IAC soon.

 

[Turdle]

simple
remove negative battery cable ( any time I touch wiring i do this)

Remove the passenger side foot panel trim, and the ecm is under there. It is held in place by a bracket.

 

[Roont]

With your live data, what are your trims? When you checked vacuum system did you smoke it or let it sit with applied vacuum and no leaks? Eliminating unmetered air will help eliminate a bunch of testing on that end and you can focus on wiring