TheSamba.com :: View topic

Mon Jul 02, 2012 10:46 am

Ok I have a new problem. I can rev the engine up while it's sitting still and it revs up just fine. When I go to drive it when I give it some throttle, the engine loses all power and revs down for a few seconds and then suddenly will pop back to full power as if nothing is wrong. It does it at all rev ranges seemingly randomly. I am currently without a fuel pressure gauge, I have one on order. I suspect that I might have a fuel pressure issue, as if there is not enough pressure when I give it gas that will resolve once it builds up and the car will go again. Also I have an extra brand new rebuilt AFM on there and it does it whether I have that one or my old one on there. Any thoughts?

Mon Jul 02, 2012 11:49 am

this is pretty much the problem I had when the outlet on my gastank was restricted by debris in the tank..

Mon Jul 02, 2012 11:59 am

Ok cool. I hadn't though of that. I have had my fuel gauge sender off recently. Maybe something fell in there. I'm gonna go have a look. Thanks!

Mon Jul 02, 2012 1:17 pm

I looked inside the tank and found a small remnant of the old sender and got it out. I took it for a drive around the block and same problem. I seems like its' hesitating, although I've never experienced hesitation with FI before. I'm stumped.

Mon Jul 02, 2012 1:27 pm

After reading some other threads I think it might be the fuel pump. I have another one from a junkyard bus, I'm gonna swap it and see if there is a change.

Mon Jul 02, 2012 1:30 pm

if you can drain the tank try sticking a pipe cleaner or something up the outlet; thats what worked for me.

could be a spark issue aswell, might check your plug gap.. could be too far out and your blowing out spark at high rpm... or bad plug wires grounding out

Mon Jul 02, 2012 1:30 pm

If you hook up your timing light at idle and rev it up, does the timing advance like it should?

Mon Jul 02, 2012 1:36 pm

Last time I checked the timing it did, which was a few weeks ago. I will say this problem started small and has grown over time. It seems to me like the fuel pump could be at fault. The problem is it's 104 degrees outside and really hard to work on it for any period of time before almost dying.

Mon Jul 02, 2012 1:39 pm

dreadlocks wrote: if you can drain the tank try sticking a pipe cleaner or something up the outlet; thats what worked for me.

could be a spark issue aswell, might check your plug gap.. could be too far out and your blowing out spark at high rpm... or bad plug wires grounding out

Thanks dreadlocks. The tank is almost full so draining 12 gallons could be a problem. I'm just going to have to drive it a while until the tank gets low enough to drain and then try that.

Mon Jul 02, 2012 2:18 pm

Do you still have a fuel pressure gauge installed on the fuel rail?

Mon Jul 02, 2012 3:11 pm

My gauge on the rail broke and I have a new one on order. I just readjusted the timing and took it for a ride around the block. The moment I press the pedal hard it loses all power and the engine revs down and will stay that way for 3 or 4 seconds. If i just keep holding the pedal down it will pop back into power and go for a bit and then bog down again. It has become very cyclical now. I need to drain the tank and stick something up in the out-port to see if it is blocked. My junk yard fuel pump broke when I tried to get the old hose clamp off just now so that is out. This stinks!

Mon Jul 02, 2012 3:28 pm

This all started not long after I fixed the EEC valve vacuum leak. Come to think, the first time it happened was that day! It has gotten worse since. Could it be possible that now that the fuel pressure regulator is getting full vacuum, which it never has before, that it somehow crapped out? I have another one I could put in there to see if it changes anything. My used FI came with 2 of them, which leads me to believe one is bad.

Mon Jul 02, 2012 4:04 pm

try pulling the vac tube off your FPR and plug the tube, IIRC the fuel pressure drops under vacuum.. worth a try.

dont change FPR without draining the tank, or at least pinch the return line at the tank.

If you got 2 FPR's with your FI kit then one very well might be bad and the PO got em mixed up so sent you both..

Mine didnt surge/cycle like that with clogged inlet port; it'd just struggle until you unloaded the engine and let pressure build back up.

You can test your current pump by doing a flow test, have it pump into a bucket and time how long it takes a few gallons and check the specs against your GPH findings.

Mon Jul 02, 2012 4:14 pm

FPR unplugged with hose plugged, no change. Although when revving it while sitting still it is much smoother.

Mon Jul 02, 2012 4:21 pm

all signs are pointing at your regulator currently, go ahead and replace it with the other one since you have it and cross your fingers :wink:

or park it until you get your new fuel pressure gauge and can verify things.

Mon Jul 02, 2012 7:05 pm

I switched out the FPRs and there was no change. I'm at wits end now. All I can do is drain the tank tomorrow and check that out until my fuel pressure gauge comes. It is really bad now to the point of not being able to drive the bus.

Mon Jul 02, 2012 10:03 pm

and its not running rich? Ignition issues usually leave the tail pipe smelling of unburnt gas.. might pull the plugs; see if your running real lean.

Tue Jul 03, 2012 6:18 am

From the smell of the exhaust I think it is running quite lean, when it runs. I really need that fuel pressure gauge. I'm going to acquire another complete set of FI components today for cheap. Maybe I can find something out that way.

Tue Jul 03, 2012 1:09 pm

Well I fixed it. I cleaned up all the grounds; they were in good shape anyway, so there was no change there. I also put in a new rotor and distributor cap as I needed to anyway, that made it idle smoother but it still bogged down while driving. I also drained the tank, it was not clogged. The process of elimination left only the fuel pump.

I went to my local parts store and the only pump they had was a new german bosch pump which normally retails for like $230. I showed them the bus depot price which is $149 and he brought it down to $169 which was great. I put it in and it runs great now. Yay!

I see now what happened. The weather got up to 110 degrees and has still hung around there. As soon as it got hot the pump started to fail. It was a used pump. Part of the problem is that one of my heater control boxes, aka flapper boxes, sits directly next to the fuel pump, and they are the early style box that just vents right there when the heat is off. I can only image that it got into the low 200s right around that pump. Luckily, I just acquired two stock '79 heat control boxes and the tubes that go along with them. So soon the heat will be venting out the back as VW intended it.

Tue Jul 03, 2012 1:14 pm

Congrats on getting it solved! Now if only this heat would back off