No CEL light, not bulb or contact

...No CEL light, not bulb or contact..:scratch:

...This is on a modified 91, 4x4, 4.0l 4door...

...All of a sudden I have a miss, a stutter , like a load up with a backfire and it shows up more prominent in overdrive on a hill...I know, fuel, vacuum, air, spark, etc...

...Before I get into all that I wanted to pull my codes but for some strange reason my CEL light now does not come on with the key...I pulled the pita dash apart to find the bulb good and replaced it anyway...I also did it from the backside and was sure it was set for the contacts...Now I'm thinking computer...

...While searching for disconected electrical connectors in the engine bay, I found a plastic vacuum line severed by the alternator which runs directly back to a "T" by a large cigar looking plastic container (1 1/2"-2" od), mounted high near the pass side valve cover...

...I can not find where it is suppose to plug into so I capped it off and still have the same sputtering...

...My initial thoughts on the sputtering is it is electrical in nature but the non working CEL light now has me worried...I am going to see if I can get a read on the codes with a voltmeter or a ...

...any Ideas on this would be appreciated and I will try to get a pic up of the vac line, thanks...

There could be something in the PCM, but I'd first make sure the CEL is getting power KOEO, and that the PCM is getting power.

You could have a bad PCM relay, blown fuse or a bad ground connection. Your fuel pump won't turn on if the PCM doesn't turn on.

Looking at the wiring diagrams I have (gotta love the internet sometimes), it looks like the power for the CEL comes off of the PCM with a pink/light green wire.

You might be able to get a voltage coming off of that wire directly and read the flash codes with a VOM or a test light.

HTH.

There wouldn't be any codes stored if the PCM never had power going into it.

..Ok, Heres where the fun begins......:scratch:...

...I pulled all the relay fuses and being **** as I am, took some sandpaper (600 grit) and cleaned each one as I checked them...I jjumped in the truck, turned the key on and finally got the CEL to come on...

..I warmed the truck up and reved it after it got about half warm in which I got a backfire...Not normal but I thought oh goodie, I'll at least get a code...Got her all warmed up, shut her off, and proceded with the mil (CEL readout) and got all pass..

...I noticed while it was warming up (90 ambient temp outside), and it was almost at full normal temp, it began to run a little rough and this neither is normal...After doing the test I went to start the truck again and no CEL on startup...

...I hate shorts...

...On another note, here is the pic of my 91's open vacuum hose..The red O represents the open end and the red < just shows the line coming forward to the a/c hose and I have it pulled up towards the hood so you can see the bend and maybe help me locate it's home...(I noticed this open line before I changed my alt and it looked like it was running to the bottom of the alt but who knows)..I am so hoping that this is the culprit but I'm still leaning towards electrical..

...I'm still needing some help with this vacuum line and the darn thing is getting worse...

Is that one of the lines that was supposed to be plugged into the backside of your missing airbox?

...Naa, but I wish it was...Mine are still intact and proper for the easy re-install for smog..

...I looked in that area though but theres nothing else there for a vacuum line...It looked like it was running thru the Alt bracket when I actually found this vacuum hose...It was severed and laying right in the hole of the Alt bracket...

Can you get a side shot, and a closer shot of it? Maybe upload the huge file somewhere instead of resizing? I know we have a picture size limit, but maybe put just the link.

If you can do that, I can go out on mine and compare. I just can't see the area you've highlighted well enough.

...not at this time.

...But if you look at the pic, dead center top, you will see the black cigar looking thing and the vacuum line is to the left of it running onto the a/c line, actually the connector from metal to hose...

...I think I got her figured out...

...First, the vacuum hose makes a direct 180* and goes behind the airbox into a harness which leads to the cab...I found a pic of it in the Haynes book on page 5.4 top left...Bad design as it will surely break with the desert heat...After I found it I got a piece of 1/8" hose and went to make the repair...The plastic line broke again on it's own while I was gone getting the hose......It's all better now...

...I also went and got some new Bosch plug wires (pn#09645= $33)and that seemed to resolve my throttle problem, especially after I found one thumb clip broken at the coil pack, #1 plug...

...Just for fun, I also resistence tested the old and new wires with my digital meter ...

1) old wire = 5.0 new wire = 25.6
2) old wire = 6.3 new wire = 24.5
3) old wire = 3.6 new wire = 21.5
4) old wire = 5.4 new wire = 8.7
5) old wire = 8.1 new wire = 9.7
6) old wire = 6.7 new wire = 1.3


...It's running like a champ but now I have an IAC problem....It's slight but definately noticable...And the CEL on, key on, is still sometimes lit...

...I previously was having a Wally World battery issue which I resolved by replacing my stock Alt with the 160 amp Alt...I also had the battery bench tested twice and it showed as a bad battery...I filled the 10 month old battery with distelled water and this all seems to be fine and bench test proper now...

...My thinking is that the battery was bad enough to limit the spark and after I got that under control, the electronic system started showing all it's bad parts, all at once...

...Now I'm off to find The best "Cleaning the IAC" thread I can find on here...