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Mad (Sean) Max
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9,602 Posts
Discussion Starter #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
 

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Ex- 6BT Square Body Man
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9,754 Posts
Maybe your cab is shifting on the frame and pulling on the throttle cable:D

Single or dual tanks?
 

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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).
 

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Mad (Sean) Max
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Discussion Starter #4
Maybe your cab is shifting on the frame and pulling on the throttle cable:D

Single or dual tanks?
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.
 

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Mad (Sean) Max
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9,602 Posts
Discussion Starter #5
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).
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
 

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Super Moderator A Country Boy Can Survive...
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14,350 Posts
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.
 

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Mad (Sean) Max
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Discussion Starter #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.
 

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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:
 

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R.I.P. Sam
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is it only doing it in the cold or all the time?
 

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Mad (Sean) Max
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Discussion Starter #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
 

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Mad (Sean) Max
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Discussion Starter #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.
 

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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.
 

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Mad (Sean) Max
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Discussion Starter #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
 

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Mad (Sean) Max
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9,602 Posts
Discussion Starter #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
 

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Mad (Sean) Max
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9,602 Posts
Discussion Starter #17
Anyone feel free to comment. Anything before morning would help.
 

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I had a similar thing. I ended up pressurizing the fuel system and finding 2 very small leaks, that didn't leak fuel, but let air in when sitting (enough to make starting after a day almost impossible).
 

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respect the DB4 5722....
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12,490 Posts
Anyone feel free to comment. Anything before morning would help.
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.....
 

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Mad (Sean) Max
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9,602 Posts
Discussion Starter #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.
 
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