'83 Quantum TD runs away (but then comes back)

[Ortho Stice]

Hello everybody, I've heard it said that these forums are where the most hardened of VW diesel-wizards hang out and so I come to you with some questions. To get it out of the way, I have read and searched quite a bit around here and that's all been very helpful.

I bought a Quantum TD wagon off some kid last month who didn't know a thing about cars yet who thought he could daily-drive a 30 year old VW. It runs and drives and really all I noticed on the test-drive was that it smoked a lot, had no exhaust left, and needed serious attention paid to the brake system. But it started right up, held an idle, everything (except the A/C) worked, and it was inspected so I took her home.

Now here's the thing; he mentioned that the throttle would hang up and said he was told the cable needed to be replaced. Upon taking a closer look, I discovered that it's not that the throttle hangs up, it's that once the engine gets farther up into the revs (around where it starts making meaningful boost) it starts to run away. If you hold the throttle lever at about halfway it'll start to run away slowly at first and then take off towards redline. Here's the thing though, if you let go it will hang for a second or two and then wind back down to idle no problem. In my searching of runaway problems I wasn't able to find anything like that mentioned in other threads.

So at first I thought I'd check to see if the turbo was the culprit; but, with the boost hose unhooked from the intake it still does it. It'll do it with the oil filler cap and vc breather both off, too.

Anyway, I'm not really looking for a "OMG WHAT DO I DO" type of thing here, moreso I just want to bounce ideas of y'all. So what are your thoughts? I'm inclined to think that well, maybe it's not oil after all? Maybe the pump or injectors are dropping too much fuel in there and it starts to run away but then when you cut the fuel it burns off the excess and then winds back down? We just pulled a running 1.6l (well it was before the headgasket blew, but fuel-wise it was good) out of a Rabbit that'll be getting a TDI soon and I thought I might swap the injectors over and see what happens and then swap the pump over (it had a turbo-pump on it) over and see if that makes a difference.

If it is oil, where's it coming from? Down the stem seals? I haven't done a compression test but if you pull the cold-start advance lever and glow the plugs it fires right up at the first touch of the key when cold and has no problem starting when hot, either.

[vanbcguy]

You could have a sticky pump. If the governor assembly is sticking it can cause what you are describing.

Might be worth starting with either a diesel purge or ATF soak for the pump.

[libbydiesel]

It sounds like the max fuel screw is in too far.

[Ortho Stice]

It sounds like the max fuel screw is in too far.

Yeah I'd read that too much enthusiasm with that screw can lead to this kind of thing. But the anti-tamper collar is still in place...

I'll try the old ATF purge and see what happens. Then swap injectors, then swap pumps. I feel pretty confident that I'm burning diesel and not oil. Well, at least not more oil than usual.

[libbydiesel]

Does the pump have the fast idle cold start or just the timing advance version?

[Ortho Stice]

Does the pump have the fast idle cold start or just the timing advance version?

I don't know, it has the pull handle on the dash that moves a lever on the bottom engine-side of the pump through an, about, 45 degree rotation.

[libbydiesel]

Does the back of the pump have this vertical rod running to the upper seesaw lever from the cold start, or does it just have the cold start lever at the bottom?

What rpm is it idling at?

[Ortho Stice]

Nope just the cold start lever. And I don't have a tach so it's hard to say. When the cold-start lever is pulled it sounds "right" which should be around 800rpm, no? Maybe I've been pushing the lever in too early, but once it's warm it seems a little slow and rough.

[fatmobile]

 Smoked alot eh?
 What color?

[Ortho Stice]

Smoked alot eh?
 What color?

Bluish-grey. I ran some ATF through the pump until the return was pumping out only red and I'll let that sit for a few days and see what I loosen up, if anything.

[libbydiesel]

The injectors can make a big difference.  They can both cause the rpms to hang and make the idle sound lower than it is.  I had a somewhat sketchy set in a vehicle of mine and the idle had to be up near 1,000 to keep the rattles at bay.  It did not audibly sound overly high idle in fact, if anything, it seems lowish.  With those injectors and the idle set at that point it would hang the revs slightly.  With the injectors changed to fresh nozzles with the break pressure very close together the same engine can idle at 750 with less vibration that it had @ 1,000 with the old injectors and audibly seems like a very similar idle.   

[Ortho Stice]

Well I'm back from tour and got back into the Quantum these past few days. After a month of sitting with ATF, I fired the car up and it started no problem but... still ran away the same as it always had. And then I noticed a pretty serious fuel leak from the pump head. Like almost slightly open faucet level of leak, haha.

So anyway, yesterday I pulled off that pump and threw a known good pump on that we had lying around. I used the diesel timing tools to lock everything up and put the new pump in the same position the old one had been in. Pulled fuel up to the pump and then started cranking it over. So it will crank and then fire and then immediately die.

Any new thoughts?

[Dakotakid]

Yeah, paste the footfeed to the floor or hold it wide open while you crank it over. Are you doing this?

[Ortho Stice]

Well a couple of things happened since I posted; While cranking with a friend watching he pointed out that air was getting into the fuel line (probably the original hose between the filter and pump) so I replaced that with some fresh hose and hose clamps. Primed the pump again and cracked the injectors and number 3 refuses to get wet.

So now I'm thinking that even though I was pretty sure this pump was good... maybe it's not? The rest of the injectors get soaked when cracked. I have yet to crack the #3 line at the pump head but I'll do that next. Perhaps I should just rebuild one of these pumps and injectors and start from square one.

[theman53]

How about just keep trying to get it running and work the air out of it.