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air in fuel when making right turn.

18K views 112 replies 17 participants last post by  akalnoski 
#1 ·
Just some research since I won't be able to take a real serious look at anything for a while.

When I make a hard right turn at low acceleration, I get a sudden increase in acceleration, just like air in the fuel. that is the only time it does it though. If I have to slow down after making the turn the idle is rough for a few secs then everything smooths out. It doesn't do it any other time. Doesn't make a lot of sense to me. During daylight tomorrow I'm going to try and crank the wheel and see if I can see anything but until I can spend some time on it that's all I;ll really be able to do.

Any help appreciated

Thanks
Sean
 
#4 ·
Single tank. But that's interesting. The cab is so rotted that i can feel it flexing when I go over bumps. The cab mounts on the DS are non existant. It does almost feel more like a pull on the throttle than air, although I do get the rough idle immediately after.
 
#3 ·
Sounds like it could be a rubber line that is a little too short or not routed properly that shifts when turning. My 'burb did something very similar. I found out yesterday the line from the barbed outlet to the lift pump input was just barely long enough when the truck was sitting on level ground and when it rocked it would tug a bit on it (a failed worm clamp didn't help matters either).
 
#5 ·
That's what I'm thinking.I redid the fuel line from LP to IP so nothing is routed properly. that was well over a year ago though. I'll take a look at all the clamps since I'll have some daylight to work with today and tomorrow.

Thanks
 
#6 ·
Does this only happen when the tank is below a certain level?

If so, it could be that the pickup tube has a hole in it due to rust.

Turn one way the fuel covers the hole, no apparent problems. Turnthe other way, no more fuel covering the hole, so the system sucks air.

That that would take time before you'd notice it at the IP. That air would have to go through all the lines, filter, hoses, IP etc, before you'd notice it.

I'm betting it's not that due to the second you turn you can feel/hear it.
 
#7 ·
I do have that problem but my tank has to be very close to empty anyhow, less than an 1/8th. so it's not really an issue except sometimes my fuel gauge lies to me.
 
#8 ·
when my brakelight switch was broken/stuck i would take corners and the trans would upshift and downshift a couple of times going into the same corner/bumps on my way to work i replaced the switch and it didnt do it anymore
IDK if thats maby somthing your talking experencing :confused:
 
#9 ·
is it only doing it in the cold or all the time?
 
#10 ·
huh? it's winter, it's always cold. It's only done it a few times. Day before yesterday for the first time -15c, yesterday same and again today a little warmer. interestingly today it happened while reversing down a hill out of a driveway. Again at low speed while just beginning to accelerate. I'm beginning to think it is the cab flexing and pulling on the throttle cable.

I ended up working today so I didn't have time to look at anything, may be tomorrow
 
#12 ·
maybe? I installed a used IP that came out off my blown engine last year. No idea of age. It has plenty of power and starts fairly easy even in cold weather but the truck has been smoking some. I think the smoking is injectors tho since it's substantially more out of the DS than PS.

I don't know what to think. i tried to make it do it by making particularly sharp rights but I couldn't make it happen.
 
#13 ·
Hi there a newbie to this site here. My experience with my 91 6.2 K2500 man 4 spd ext Cab w/ long bed and currently with 265,000 miles!!!, I found a few years back the same- making a turn and the engine would surge while at a lower speed. I found everything as it should be (hoses, lines, cable etc.) except the electric lift pump was out and the engine still started and ran fine. Although when starting cold it would smoke a blue/ gray for a few(5-15) seconds before clearing up. After replacing the electric lift pump problem went away. also verify the fuel relay. Good luck.
 
#15 ·
hmm tghat's interesting. I've done the lift pump test that I know of (mechanical pump) and it passes but I think I have a pump for an sbc rather than the 6.2
 
#16 · (Edited)
So I'm finally going to have some time tomorrow to look at things. Here's an update so far.

Have had many difficult starts including 2 no starts. Once I got it towed and we thought it was bad fuel but I don't think so any more. The next time my mechanic came down the next day and after almost an hour of bleeding air we got it to start, with one start then die in the attempt.

I have a clear line on the return and there are very fine bubbles coming through. Not always but they are present. there is absolutely NO signs of a fuel leak anywhere. So this means what? It's after the fuel pump or before?? Maybe the fuel filter? There is no fuel in the valley and no sign of fuel at the throttle seals. I've tightened and re-tightened all the hose clamps and the fitting at the fuel pump. Also there is no fuel in the oil. The situation happens regardless of the amount of fuel in the tank. Although the 2 no starts were when the tank was quite a bit less than full although I added 40 litres/10 gallons , bringing the tank up to almost full and still had the no start situation.

Oh and i do have a very small fuel leak in the return system. In the steel line just above where the pass side injectors return into the main line. I don't think that could cause these problems though could it? I've had that leak for 2 years or so. It's always drained the IP return in the bottom 1/2 of the return but the top 1/2 stays full at least that was the case a couple years ago when i had the clear line on. I removed it quite a while ago because it was getting brittle. I just put it on again an hour ago or so so I'll have to see if the top 1/2 is draining now. If so could the siphon effect be doing that? I know lots of questions, lots of variables.

Tomorrow I'm going to pressurize the system. I'll also use some clear line most likely if that doesn't work. Any other suggestions?

Thanks in advance

Sean
 
#17 ·
Anyone feel free to comment. Anything before morning would help.
 
#19 · (Edited)
maybe your advance plunger shaft seal is pulling in air.. we have 2 pumps that do it, and we just did a high idle mod switch and it stopped doing it, and we are in the process of re-sealing a pump now... exactly the same problem, but we run an electric fuel pump, so there was less time to bleed it... although it did it just under load.....
 
#20 ·
Well she started and stayed going yet today. After finding one leak and replacing that line I still had problems. Noticed fuel in the frame channel so bypassed all the steel line from lift pump to as close to the tank as I could get. Very little fuel came out of the steel line when I cut it. Put some clear line on and cranked it 4 or 5 times. Barely any fuel in the line. I'm going to try to get it started with a 5 gallon jerry can.

The really weird thing is that when I try to start it there is more air than fuel going through the return, but when it was running yesterday there was very little air in the return line.

this is really annoying.
 
#22 · (Edited)
try unplugging your advance on the IP..... and maybe upgrade to a electric lift pump.... princess sells them for like 70.00..... and redo all the lines in good rubber, double clamped.... i would look at dropping the tank too... maybe the sender lines are rotted and pulling air...
 
#21 ·
Meant to say it hasn't started and stayed going yet today.

Tried the jerry can. Maybe my lift pump is done because there's some fuel in the line but not much. And there's nothing at the fuel filter at all now. Interesting that the return line still has fuel in it. Getting dark now. Try again in the morning.

Did I say that this is really annoying.
 
#25 ·
And there are lots of puddles, clear oily puddles, black puddles, red puddles. No green puddles tho. Now that I say that my rad will blow on me once the ***** is started. It's funny. A month ago a guy was walking past my truck while I was taking a break and asked me what year the truck was, Oh '87 huh and still reliable huh? I said yeah not too bad. Guess what started happening a few days later.
 
#26 ·
Lack of progress report. Electric pump wouldn't draw fuel. it partially fills the clear line then won't draw anymore. I put a finger on the suction side and I can feel a bit of suction but not much. Tried to gravity feed. That wasn't working either. Enough to fill the filter but that's about it. Removed the mechanical fuel pump, looks fine, and when I cover the suction end with my thumb and push the lever I can feel some suction. Again though, not a lot.

Saw a drip come from the bottom of the filter base but there's been so much spilled fuel that I don't know if it's from the filter base or not. Regardless I still ahve to figure out why nothing will draw fuel.
 
#29 ·
took a look at a '90 with a decent body and 305 today. $800. It's very tempting. Park the old ***** and try to find a new body or something. Hard to justify the time for a truck that is such a piece of junk.
 
#30 ·
Buy the 1990 and stick the 6.2L in it! Itll give you a good chance to run all new fuel lines new wiring for the lift pump, etc. Good chance to start clean.

Good luck in whatever you end up doing. I wish I could be of more help
 
#31 ·
sorry to hear you say that but I'm in the same boat.If it wasn't a 3/4 ton 4x4 I wouldn't bother.God knows I've spent enough on it to have bought something decent. But it sure is fun to drive when it works.
I wonder if the sock or whatever is on the pickup end of your fuel line, in the tank, is plugged.
 
#32 ·
I'm thinking of doing the swap into the '90 but it's a short box and I'm not a fan. Also it's a 1/2 ton and I like having the 3/4. My mechanic has a an '88 3/4 4x4 that he isn't driving. 305. It needs an exhaust though. If I bought the 1/2 ton it would just be to get me through the winter and to a more profitable time of year.

Yeah I've spent enough on it so far it seems nuts to stop. The sock may be plugged but that still doesn't explain why I can't suck fuel out of a pail.
 
#33 ·
The 1/2 ton could be fixed.. Its the short bed thats the problems. The only short bed I want is in a off road rig.
I'm gonna do some serious thinking to try and help you figure out whats wrong..

Did you try a new fuel filter and fuel lines? Maybe now would be a good time to swap a spin on filter?
 
#34 ·
My thinking at the moment is this.

1. Failing fuel pump. It does work some tho cause I put my finger over the suction side and pumped the lever a few times and got some suction. Not sure of why I can`t suck fuel out of a pail even with the damned electric pump. That`s just weird

2. Leaking fuel filter. When I think about it, the problem got a lot worse after replacing the FF a few weeks ago. Also it took a LONG time to get the truck going after the filter change. Then I had a no start the next day. I've felt fuel at the bottom seam but there's been fuel everywhere in the last few days.

3. Various pin holes in the supply line. I found one hole that was under a zip tie that was holding a return line to a supply line. Also fond some a clean area of fuel line along the frame rail. Nothings clean on this truck. Don`t know if there was a leak or not but I cut the line as close to the tank as I could get. Lots of old dirt where I cut so no fuel leaking in that area or above.

4. Possible problem with the pickup tube, that one I`m not so sure about though since when it`s running it runs with very little air then without warning there`s huge air and stall then no start.

5. My disintegrated cab mounts make the cab crush part of the pick up tube soft line. Don`t know if this is possible but the no starts have been mostly when parked with the pass side up on a snowbank. Surging has been most common when making turns, both conditions that make the cab move around.
 
#41 ·
My thinking at the moment is this.

1. Failing fuel pump. It does work some tho cause I put my finger over the suction side and pumped the lever a few times and got some suction. Not sure of why I can`t suck fuel out of a pail even with the damned electric pump. That`s just weird
Barring some act of god, I's say the LP is no good. If it won't suck even from a pail unless the line you have from the pump to the pail is bad.

2. Leaking fuel filter. When I think about it, the problem got a lot worse after replacing the FF a few weeks ago. Also it took a LONG time to get the truck going after the filter change. Then I had a no start the next day. I've felt fuel at the bottom seam but there's been fuel everywhere in the last few days.

3. Various pin holes in the supply line. I found one hole that was under a zip tie that was holding a return line to a supply line. Also fond some a clean area of fuel line along the frame rail. Nothings clean on this truck. Don`t know if there was a leak or not but I cut the line as close to the tank as I could get. Lots of old dirt where I cut so no fuel leaking in that area or above.
Common spot for these unseen to the naked eye is on the fuel line pickup right where it bends to the tank.

4. Possible problem with the pickup tube, that one I`m not so sure about though since when it`s running it runs with very little air then without warning there`s huge air and stall then no start.
See above
5. My disintegrated cab mounts make the cab crush part of the pick up tube soft line. Don`t know if this is possible but the no starts have been mostly when parked with the pass side up on a snowbank. Surging has been most common when making turns, both conditions that make the cab move around.
Sounds like you know where to look.
I would have a fuel pressure gauge handy as well. You should see 4-7 psi min. you should NO air.
Hope that helps.
 
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