fuel pump diagnosis: stalling when warm

[CrashTest]

I'm having some weird issues with my 98 2.5 and think it might be the fuel pump. Before I drop a few hundred and get all stinky swapping the pump - is there any way to test the pump?

I was driving today - normal commuting and had no issues. Parked, returned, drove, everything fine. Then later in the day I hit some nice back roads, high RPM, high load stuff. When I pulled up to a stop sign the idle began bouncing up and down, almost stalling. Not sputtering or running rough, just up and down. At the next stop sign, the idle would dip and it would stall. It would immediately restart with the key, and if I feathered the throttle it would be fine. If I put it in neutral and left the throttle alone it died.

I read some accounts of bad pumps causing stalling when hot. It's odd that at high RPM high throttle opening, even in bend, I had no hesitation or stumbling but at rest, idle it would die. If the pump is going, wouldn't it have trouble with high-demand situations?

I pulled the relay and popped the cover off. No broken connections apparent, looks fine. The car sat maybe 10min and is behaving better. Idle a little wavy after throttle blips in neutral but no stalling.

Ideas?

[tommy583]

I had the same problem last summer. I cleaned the throttle body and the idle control valve. Ran great after that. Cost was one afternoon and a can of carb cleaner.

[woodsman]

when mine went it displayed a UNwillingness to rev high and was down on power. It also stumbled when at low revs. The next day it wouldn't start. I wonder if you've got a bad tank of fuel? Checking the fuel pressure is easy if you've got a $50 pressure tester (schrader valve- same as most cars).

[heliguy]

Originally Posted by woodsman

when mine went it displayed a UNwillingness to rev high and was down on power. It also stumbled when at low revs. The next day it wouldn't start. Checking the fuel pressure is easy if you've got a $50 pressure tester (schrader valve- same as most cars).

Same symptoms when mine went.

[particlewave]

Originally Posted by tommy583

I had the same problem last summer. I cleaned the throttle body and the idle control valve. Ran great after that. Cost was one afternoon and a can of carb cleaner.

This is a good place to start and most likely needs to be done anyway. Doesn't sound like fuel pump.

[CrashTest]

Thanks all - will clean the TB and ICV today and see what happens.

[san rensho]

Could also be a vacuum leak. If you have a scanner, check the MAF and fuel trim values. If the Maf value is lowand the fuel trims are positive and high, then its likely a vacuum leak.

[CrashTest]

Took the ICV off to clean it - two things. Clearly the throttle body has never been cleaned. And the plastic body of the idle control valve is cracked. Going to replace the valve and gasket and see what happens next.

Hey san rensho - happen to have a 3Rensho?

Here's my restored 86:

[CrashTest]

edit: $270 for a replacement - silly.

Turns out the door, or valve, inside was stuck. It's freed up now - going to soak it and clean it a little more before shelling out $300 for a new part. Yikes.

[woodsman]

thanks for the update and may I say- I love that bike, including the colour!

[san rensho]

Originally Posted by CrashTest

Took the ICV off to clean it - two things. Clearly the throttle body has never been cleaned. And the plastic body of the idle control valve is cracked. Going to replace the valve and gasket and see what happens next.

Hey san rensho - happen to have a 3Rensho?

Here's my restored 86:

Yes I do! I got one of the first to come from Japan, but its a restoration project at this point. I need to find an old campy group to bring it back to its former glory.

Yours looks great. Nice conversion. SS or fixed.

[tommy583]

I feel like i actually helped . I hope it works out for you. I read on the forum somewhere that the ICV is also a VW or Audi part that looks exactly the same for much cheaper.