Here's a weird one!!!

[joelb]

Ok, I've just had something very strange happen to my '94 Sport. My wife called and told me that it was idling very rough and it kept cutting out on her. When I cranked it to check it, it was indeed idling rough, and I could here the loud hiss of a loose vacuum line. Nothing wierd so far, right? I opened the hood and found the source of the vacuum leak. Screwed into the side of the intake (driver's side) back close to the firewall, there is what looks like a manifold for several vacuum lines. There are 4-5 different hoses that feed from this manifold. One goes to the brake booster and one goes to something that has to do with the throttle. I haven't traced the others yet. Three spickets were sitting open when I found it (hence the massive vacuum leak). The two hoses coming directly out of the rear of the manifold (toward the firewall), and one directly in front were blown off. There is also some substance, either brake fluid or oil, all over the hoses that were blown off. What the heck could have happened? I have yet to find the hose that belongs on the spicket in the front of the manifold. My hose schematic has faded beyond recognition, so I don't have anything to aid my search. Does anyone know if a hose goes on this spicket, or is it just capped off? I've replaced the two hoses in the rear and capped the one in front and everything is running fine.
I recently replaced the driver's side brake caliper. I don't know if anything could have happened during the repair that could have caused this. I used a hand vacuum pump and a siphon bottle to bleed the brakes after the repair. That's the only thing about this repair that was different from other brake repairs I've done. That's the only work that's been done on the truck lately. Two weeks and 800 miles have gone by since the repair job.

I don't have any great theories on this one yet. Any insight would be GREATLY appreciated.

Thanks,
Joel

 

[Gofast]

Picture.....

Hope this helps. I have an empty hole under the hood so I can't trace any lines.

 

[MOTO MIKE]

I checked my 94 Limited and found that one spicket in front was plugged.......guess you got it right.....have you check the engine for back pressure? or perhaps a burnt valve is to blame. check the engine compression to see what shape the engine is in, the only reason i can think of that would blow off vacuum lines is a sudden pressurization in the intake manifold..... a burnt vavle is the only thing I can think of that could do that, but your truck wouldn't run THAT well......maybe the EGR valve???? could it have backfired?????

 

[joelb]

Many thanks for the vacuum diagram and the confirmation that the one spicket was plugged. I doubt that it's a valve problem because as you said, the truck wouldn't run very well after I plugged all of the hoses.

I posted this question to another forum and it seems that one of the vacuum lines on that manifold goes to a "transmission modulator valve" or something like that. I can't recall the exact name that was used off the top of my head. Evidently this valve can go bad and squirt tranny fluid up into the vacuum hose. I didn't even know I had a "transmission modulator valve" but it sounds like a likely culprit. I'm going to try to find time to crawl under the truck today and check it out.

Thanks again

 

[Sschultz]

If your trans modulator goes bad ( the diaphram gets a hole in it)the truck will appear to be burning oil out the tail pipe. Also you notice that your trans fluid will be low. You stated that you just had or did the breaks. I've noticed that if the master cylinder cover is removed when the calipers are compressed rappidly( to allow room for the new pads) , an overflow possiably even a small shot of fluid can hit the fire wall and some of the components mentioned.

 

[joelb]

Well, it's the tranny modulator all right. I pulled the hose off of the modulator and had to jump out of the way of a stream of transmission fluid. I got the parts the other day, but it's been snowing like crazy, and I don't have a garage! Hopefully I'll get a chance to put it back together before spring .

 

[brandon11]

Originally posted by Sschultz
If your trans modulator goes bad ( the diaphram gets a hole in it)the truck will appear to be burning oil out the tail pipe. Also you notice that your trans fluid will be low. You stated that you just had or did the breaks. I've noticed that if the master cylinder cover is removed when the calipers are compressed rappidly( to allow room for the new pads) , an overflow possiably even a small shot of fluid can hit the fire wall and some of the components mentioned.

Trannys are a very big weak point of mine, would this problem cause erratic shifting @ around 60-70 mph ?

 

[joelb]

[/B][/QUOTE] Trannys are a very big weak point of mine, would this problem cause erratic shifting @ around 60-70 mph ? [/B][/QUOTE]

Hmmm, maybe, I know the modulator is tied into determining the shift points. It's easy to see if it's bad. Look for the modulator on the passenger's side of the transmission directly above the catalytic converters. Pull the vacuum hose off of the modulator and you should find plenty of fluid in the hose if it's bad. I don't know if there are any other failure modes for the modulator or not.

 

[mdrut]

yes, just hope there's no permenant damage. make sure you check your fluid level before hitting the road again, and if it was me, I would replace the filter and fluid anyway ,since you're already under there and dirty

 

[Chad Summers]

Have you got to changing that modulator valve yet? It is a lot of fun.. I had the exact same problem in my 94 and that fixed it.. It ran fine other than losing fluid until I took it on a long trip and I think the fluid runnin through the engine finally got to be to much for it. anyway, I replaced it and its fine now.. well other than now I'm getting the 332 egr code.. argh.. hehheh As for changing the modulator, I dropped the tranny crossmember and dropped the tranny down onto the tcase skid plate to make room to work on mine.. I spent a few hours trying to get to the heat shield till I tried that.. took about half an hour to finish up after that.. good luck.. oh yeah, don't lose the lil pin thingy out of the old one..

 

[pakers]

I just spent an hour trying to get to my modulator on my 93 XLT and could not figure it out. Could you give more detailed info on how you changed yours? When I pulled the vacuum hose off it, AFT just poured out, so I know it needs to be changed. Thanks.