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Truck Runs Real Rough, Please Help

ak diesel driver said:
pressure read at the drain t is prefilter so a clogged filter could still starve it for fuel
Click to expand...

:iagree:

A clean filter itself can cause a significant pressure drop to the IP.

Also, air is more likely to enter when LP pressure drops.

Seems as though the OPS and LP are running, and now you know how to test those to quickly eliminate them as issues. As long as there is readable pressure at WOT then the LP is likely not an issue. Testing voltage at pin F assures you that the OPS is sending voltage, but not that LP is running, pressure tests proved LP was running.

Most people searching for air will put clear fuel line on IP return fitting to watch it, but at idle may not be very noticeable. Aces put a clear line on the feed and watched it with a sightglass and could see the little air bubbles.
 
Okay Guys, I changed the filter, The one that was in it was for sure all used up. I took it for a test drive and as soon as I would give it half throttle or better it would run real rough. Once I was able to hit passing gear where the rpms would go way up and it ran real rough again. One of the times it would run rough the service engine light came one. I drove around and floored it a number of times with the service engine light on and it started to get better. I continued to drive it and drove it hard with the peddle to the floor once in a while trying to get things worked out. It ended up not running too bad. I figured it was going to be okay.

I then decided to take a back street and shut it off and left it shut off for about 3 minutes. I then started it and the service engine light was off. As soon as I gave it good throttle right away it started to miss and run rough again. This time when the service engine light came back on it continued to run rough all the time when I gave it half throttle or better. Fuel pressures were still good. I am lost.

Is it possible I got some bad fuel? I filled up from an empty take about 4 days ago and have about 1/2 tank left. The problem just started yesturday. I am now going to go out and loosen up the fuel cap and try running it that way. I am just thinking but do I need to reset anything to get everything back to normal? Any other ideas guys?

about 3 weeks ago the exhaust pipe broke off just before the muffler. It is loud but I wouldn't think that would cause this problem? a few years back the vacume pump started making noises and I am not sure it works any more but still seemed to have enough power and the ticking sound it was making didn't bother me and I don't think being it is a 95 that the vacume pump would cause any problems? I am lost on what to try next. Any ideas, everyone has been great here. I am not very good with diesels but can catch on pretty fast.
 
Yeah I never understood putting the clear tube n the return. I have had more luck using it inline to the IP. Diagnosed the burb right quickly it did. There should be no air but remember one thing, when you put the clear tubing on purge it into a coffe can or something until a fairly steady stream of fuel comes out then connect to IP or you could actually air lock it.
 
You need to find the air leak is all. That is the thing you have not troubleshot yet and most likely cause of your issue. Youve been eliminating possible causes of air entering the system, and now you are at the point that there is an actual hole in the line between the fuel tank and the LP. This is very common.

If the vacuum pump wasnt working you would not have any boost and the computer would code a DTC 78. Unless you switched the turbo to a manual spring wastegate actuator.
 
Okay guys, You all are a great help to me. I did go out and and drove it again. It was hard to start. What do you guys think if I said I might have a pmd going bad? I have been doing alot of reading on that also later this afternoon. Last september I put a new d-tech on. I also put the harness on it and mounted it to the front bumper on a heatsink just behind the liscense plate. I just got it to start and I let it idle in the drive way and it quit just like I shut the key off. I loosened the fuel cap up and drove it down the road and it ran rough. The service engine light came back on. The weird thing is the burb seems to run alot better once the service light comes on. I can hold the rpm's at 2000 no problem. But one thing that isn't working is the cruise control. I think I have read that the cruise control might be an indicator that the pmd is bad. I did have an extra standyne one here that I thought was good but when I plugged it in the burb wouldn't even fire. What you guys think about it might be a pmd problem? Hard starts rough running and quits sometimes for no reason and the cruise control doesn't work. That might be a pmd issue?
 
PMD wont cause all those codes you posted. clear them, drive it again and set SES and check them again. Air will cause it to stutter and stall.

It will run better once SES light comes on because it sets backup fuel mode which is high idle and fixed pulse width. so it stops trying to measure things as precisely and just uses Crank Sensor instead of trying to rely on OS which is getting messed up because it cant see clearly through air bubbles.
 
Darn you guys are full of information. Okay dumb question but what is the best way to clear the codes? Just when I think I was going to order a new pmd to cure the problem you guys come up with the bubbles in the fuel. Okay, different direction I guess. You guys are a great help. what clear line would I get? Should I run it from the filter canister to the pump? Do you guys know of where there might be some pictures of this install? I know Acesneights said something about a sight glass? It might be hard to find clear hose that will hold up to the diesel fuel? Thanks guys.
 
From this DTC thread which can be found by finding DTC in the technical library (which I know is not immediately apparant to newcomers) http://www.thetruckstop.us/forum/showpost.php?p=50700&postcount=3

3. It is helpful to the diagnostic process to know when codes are setting, particularly if there is more than one. Hence, clearing the codes is something you may wish to do. Clearing the codes may be accomplished by simultaneously depressing the brake and accelerator pedals fully while the PCM is in diagnostic mode (terminals A and B connected). It will not appear that you have cleared the codes until the next time you power up in diagnostic mode, however.

Make sure you leave them both fully depressed for about 30 seconds. Then shut ign off, turn ign back to on and check to make sure you just get code 12. remove jumper in DLC connector before starting truck
 
Any hardware store farm supply whatever. Sightglassing is just a term, not a tool in this app. Just use I guess 1/4 inch clear tubing. It will hold up to diesel just fine for testing purposes. Yes long term it will get hard. I use a barb and connect it to the line that is going to the IP and use about 2 ft of clear tubing and hook to IP. REMEMBER to purge fuel before connecting. If you see bubbles what I would do next is get a fitting(Auto parts sells fuel line repair kits with right end on it) and disonnect the fuel line at the infleunt side of the LP and then run the hose into a 5 gal can of nice fresh fuel. Then disconnect your clear tubing at IP and again purge into a coffecan or pail , whatever. when fuel flow is nice and steady, reconnect to IP and run. If airbubbles are gone then your problem is between LP and tank, probably closer to tank but fuel lines do rot along chassis as well. You'll have do do a serious of pressure tests on the line to find the leak if it's not obvious but we'll touch on that later. First see if air in the fuel IS your problem.
 
Buddy, Great thread about VW_Lopo. Mine has about 220,000 miles on it also. 95 burb and in Wisconsin they like to use alot of salt in the winter so you might be onto something here. The only thing different is mine doesn't get any better when I loosen the fuel cap.

I did clear the codes and 18, 35, and 54 showed back up. code 19 didn't show back up. You guys still think it is a air leak?

I will get the some 1/4 clear hose and a barb and connect it to the injection pump and run it and look for bubles. Acesneights, Thanks for the info on hooking the clear lines up.
 
Okay Guys, I had alot of good reading and alot of great help Today. Thanks and Tomorrow I have a few things to get done. My son was sideswiped by another car so I have to get a couple of estimates and I have a date with the dentist. But I will try to get the items together. Thanks everyone for the great help Today. Great site and a great bunch of people here.
 
Okay Guys, finally quiet raining here so I was able to work on the 95 Burb again. I got the 2' of clear line put on. Got to remember this burb sat for a day or two without being started. I had my Son start the Burb up and it ran like like a million bucks. There was no bubbles in the sight glass at all. When I took the line off the injector pump the clamp was loose. I thought I found the problem, Mabey. He ran the rpm's up and down while I was looking for any bubbles in the line. Didn't see any and it sounded real nice.

We then headed down the road and drove around for a good 15 minutes. It had great power and didn't miss a beat. I was convienced it was fixed. We then drove across town to my parents house and shut it off and spent a good 1/2 hour chatting with them. We got in and as soon as I started it up it wouldn't stay running. Heat Soak? It just wouldn't stay running at all. Just ran rough and would quit.

We then grabbed a bottle of water and dumped it over the injector pump. It started up and seem to run better. Not perfect but at least it did run. Reved the motor up and kicked it in to "service engine soon" mode and it did run better. But it isn't right. We checked for bubbles again and didn't see any at all.

Cruize control still doesn't work. It might have been a fluke pouring the water on the injector pump also. While the engine was warm from sitting it ran like crap. should I go out and place a garden hose on the pump and let it run on it for a while? It is just strange that it ran real good around town until we stopped. You guys don't think the pmd is bad making it run rough causing the codes to set? It is like it ran good and then when I let it sit something got warm while sitting. It just took a while for a part to warm up to malfunction? Thanks guys.
 
With my spare pmd it sets code 35 and cruise quits. If you had a spare pmd it would be worth a try. Also try disconnecting the CPS and see if it runs better.
 
Okay, I tracked down a guy that has a 95 pickup and he had his pmd mounted on the fender wall. He came over and we drove my burb around until it got warm and it started running rough again. We then took his pmd off and put it on my burb. Still ran rough. So we eliminated the pmd.

I showed the guy that it ran better once the service engine light came on. It was still lacking power but at least it didn't seem like it was running on 6 cylinders when I gave it half throttle. What do you guys think now. Did I read somewhere that I could put water on the pump and see how it acts? Or is the water trick for the pmd if it was mounted to the pump?
 
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