no return to idle, bad hesitation

[smolkin]

Well, like the title says, for the past couple of days my old no-idle issue has returned. After revving up it just stalls, it will not return to a nice idle. When you initially depress the accelerator, it hesitates for several seconds, then revs on up OK; let off and it stalls. It likes to do this when I'm stopping and turning, especially if there's oncoming traffic. Bottom line: If I can't fix this, I have to get another vehicle. It is going to get me killed.

I am at my wit's end. Today in desperation, I installed a clear return line at the filter head...I am getting alot of foamy bubbles. A WHOLE LOT. So I bypassed the FSV and the Vegtherm loop. Still the same. I traced all the fuel lines from the rear tank (only one I use anyway) and they are all OK. The Vormax and its associated lines are OK. The lift pump is 3 months old, lines are OK. The IP is 1 year old. The hard lines got new olives when I put the IP on. I put a new fuel filter on today (to rule that out). What else can it be?!? The only thing I haven't checked is the tank pickup (OEM and tank is currently FULL) and my injectors and returns are old but not visibly leaking. Do I need to drop the tank this weekend, is there anything else I can check?

 

[93f250idi]

Any leaking return lines? Maybe bad lift pump?

 

[smolkin]

Any leaking return lines? Maybe bad lift pump?

I put on the lift pump in June to try to fix this problem last time it happened, it was brand new. Not that that means anything, I guess, it could be defective...how would I tell? The pressure at the Schrader valve is about the same as it always was. And it didn't fix it then; it only went away after I put the Vormax on, which replaced an '83 OEM w/s (also, the filter restriction gauge is still in the green).

My returns look a little ratty but are completely dry. I was holding off on doing them until I could afford injectors. Can they be bad and still look OK?

 

[93f250idi]

All the ones I've seen bad were wet. Try changing the fuel filter again and see what that does.

 

[smolkin]

All the ones I've seen bad were wet. Try changing the fuel filter again and see what that does.

The one that's on there has about 3 hrs and .5 miles on it! I just put it on. The "old" one was 3 months old, and post-mortem revealed a very small amount of gunk...but nothing major. It wasn't clogged. I just replaced it because, as previously stated, I am at my wit's end. And I just re-traced everything again, found a slight dent in a steel line, but it's not leaking.

This is what I see at the clear return: Idling, no bubbles. I rev it up, it hesitates, but no bubbles. When I let off the throttle, then I see lots of bubbles. And it stalls. Does this help?

 

[93f250idi]

Hold the rpms at like 2500 for a minute or so and see if it bubbles.

 

[smolkin]

Hold the rpms at like 2500 for a minute or so and see if it bubbles.

OK, just did this. It doesn't bubble until I let off the throttle, and then it stalls. It is definitely getting worse, only by very slowly letting off the throttle will it go back to idle, and it's lower RPM than usual. And since I have a C-6 I can't do that while driving. I can only get back to idle without stalling if I feather the actual throttle lever, I can't seem to do it with the pedal. From what I am seeing and my limited understanding, I think it's a restriction somewhere maybe...when you initially start it up, it idles ok, it seems to be when the demand for fuel increases that I'm sucking air.

 

[icanfixall]

Try tightening up the fuel line from the filter to the injection pump. Also the filter inlet line nut. The bio fuel may have eaten the square o rings. I understand you changed them but try the tightening anyway... It may be a cheap fix.... Is the filter really tight or can you tighten it a little more. The injection pump has a screen filter in the inlet nose cone. Hopefuly that wont have to come off because there is plenty of small imperrer vanes in there plus you need to remove the pump to see what your doing in this area.....

 

[93f250idi]

When u let off and it bubbles means air is getting in right? When u rev it up it's taking the pressure off of the system because it's going in the motor. When inlet off the pressure builds back up and it sounds like it's pushing the fuel out somewhere when it does that

 

[smolkin]

OK update: I tried running it directly off of a gas can to rule out a clogged pickup. It is no different. The bubbles are less now...but the way it runs is actually worse. I am beginning to think there is a problem at the IP.

icanfixall-- I have the nuts bottomed out already! They aren't leaking, at least not that I can see. The filter is hand-tight+1 turn with a wrench. I would take the IP off but I HAVE to have the truck to "drive".

The way it's behaving makes me think it's an internal IP problem...? I will try to make a video of it hopefully tonight, but it's dark already.

 

[gandalf]

You said that the IP is one year old. That would make it a rebuilt IP. Who rebuilt it? That can make a difference.

Your line nuts are bottomed out? That doesn't sound right. Somebody?

 

[The Warden]

You said that the IP is one year old. That would make it a rebuilt IP. Who rebuilt it? That can make a difference.

Your line nuts are bottomed out? That doesn't sound right. Somebody?

I agree with Ken; it could be a pump issue. As he asked, who rebuilt it? The problem may be with the governor. I actually had this problem once, although it wasn't bad enough to kill the engine. If I let off the throttle, the engine would idle so low that it was about to die, before the governor caught up and brought the engine back up to its normal idle. I ended up heavily overdosing with PowerService for a few fill-ups and it started working properly. I'm pretty sure my issue was caused in part by a low quality rebuild and in part by bad fuel...and, for that reason (plus some mileage/power issues with my M-B), I will never use Shell diesel again unless it's a desperate emergency.

One other thing to check on the IP...with the engine off, move the lever to full throttle while watching the driver's side of the pump...there should be an arm that pushes a metering valve on the bottom in (i.e. towards the center of the pump) as the throttle advances, and the arm and valve should move back out as you let off the throttle. This is your timing advance...it's possible for this to stick and cause a problem.

As to the nuts being bottomed out, I can't say for sure...I have yet to replace the "olives" on my lines. But, with the old olives, my hard lines usually do end up just barely bottoming out...but I've never had a noticeable fuel issue that could be attributed to them.

Maybe that'll help some...good luck!

 

[Full Monte]

What about your accelerator cable? Those things have plastic parts inside the spring that can come apart and do funny things to your throttle response.

 

[smolkin]

Well, last night was fun. I tried to drive it up to the Walmart up the road (about 3 mi). It kept stalling, but I finally made it and got a jug of DieselKleen. I dumped a double dose in the tank and puttered around the parking lot for an hour. On the way back home it tried to stall but didn't, which is an improvement I think. I am hoping that I can drive it today.

The Warden: Come to think of it, I did get fuel at a new gas station...just to be safe, I'm never going there again! As for the IP, it was a "brand-new" rebuild locally by Test Calibration, they do their own reconditioning. I had heard good things about them, but...?

As far as the advance piston, it appears to be moving normally, and although my throttle cable has seen better days, it isn't binding and moving the throttle lever by hand makes no difference.

In about an hour, I'll start it up and see how it's acting. I need more coffee, last night was a rough one.

 

[gandalf]

Warden has hit the other point I was trying to think about last night---the metering valve. Your symptoms match a sticking metering valve. Dying on return to idle is one of the traditional metering valve indications.

Give it a heavy dose of DieselKleen, Diesel Service, or something similar. Even go so far as to pull the fuel filter, fill it with Diesel Service, screw it back on, and run that through the engine full strength.

I'm not familiar with the outfit that rebuilt your IP. It's easy, though, to get a bad rebuild. That's the reason so many people here have gone to Russ, TYP4, and Mel, Agnem, for their rebuilds. They both put out a known-good product.