Tonight I took the 928 for a quick blast down the road, I felt this before but didnt really think much of it, I was at WOT from about 10 mph all the way up to 110, then let off, the whole time I felt a slight surge in acceleration, the plugs,wires,fuel filter,cap and rotor are not too old. Any ideas? Maybe a vacumm leak?

 

I have this similar problem on my 1987 928S4. Haven't had a chance to take a look at the problem though. Except, mine isn't a slight surge, it's pretty big, but sometimes it runs smoothly and the car pulls very very hard.

 

Hey justin,

You might want to check with Richard Andrade (rich9928@earthlink.net) or Carl Faussett (info@928motorsports.com), and see if there are any particular conditions that would cause surging on a K-jet car. I think your initial guess is right, surging is usually attributable to a lean condition.

 

Just noticed my '92 GTS doing this the other day and then again today. It has been VERY COLD (at least for Austin) and I have not noticed it before. It is pulling like a freight train, but there is a subtle but distinct surge going on.

Any thoughts guys?

 

Pretty simple to see if it's the MAF. That would be my starting place for an otherwise fine running car.

Not sure if extreme cold can mess with them or not, maybe JDS will tell us. Never really thought about it before but it's been unusually cold here in TX, maybe this is normal we just never noticed it before

 

It's usually called "lean surge" by the techs, cause that's what it usually is.

Possible causes include:
- Fuel flow problems. Not too common, but it can happen. Easiest way to check is with a fuel flow test. If you pass the applicable fuel flow test, quit worrying about fuel pumps, filters, etc.
- Fuel control problems. These include a faulty or maladjusted WOT switch, Temp II or wiring problems, Temp I or wiring problems (early cars only), mass air flow sensor or wiring problems (LH cars only), air flow sensor problems (earlier cars), etc. Normally, a vacuum leak bad enough to cause lean surging will cause serious starting or idling problems as well. CIS cars have their own unique set of problems with fuel control.
- Ignition timing. Not common at all, but can happen. Temp II sensor again, vacuum advance/retard on some cars. Don't forget the vacuum line running to the EZF ECU on the early 32-valve cars.
- Everything else. Cam timing, transmission problems, etc. Not common, but check if the more common causes look OK.

 

MAFs are fully air temp compensated, so they can measure air mass accurately.

Just for info, nothing to help this early car.....

 

Thanks John, I was just wondering out loud.