sullivs

I'm having a problem that has been elusive for the past few months. At the last DE, my engine was missing at rpm's above about 3500 in the upper three gears. I do not notice it in first or second gear. It came on suddenly, and the best way I can describe it is a soft "missing" when accelerating hard in third, fourth and fifth. It does not pull as well in the upper gears now, and feels in the seat of the pants like it is not running cleanly.

My local shop thinks it is an air leak. However they cannot locate anything leaking. I have since replaced the air filter, spark plugs (the lower ones were horribly used), distributor cap and rotors. My car has 90,000 miles on it, and is pretty original, and until now runs very well.

If driven around town, it cannot be felt. But once you get onto the highway and push it, you can feel the slight missing. Anyone experience a problem like this before?

Thanks for the help.
Steve

axl911

Have you check your distributor belt? A broken dist belt can cause pings and missing.

sullivs

Thanks, I will check it.

Roygarth

I had a similar problem recently, it was a failed DME Relay (black thingy in the fuse box!) Easy fix (even for me!) £20 part, pull out original, push in new one!

Piers
1990 C4 Coupe
59K Miles

Jeff Curtis

My car was doing this for awhile at track events, just a slight mis-firing under load when pulling hard in 3rd...it disappeared.

I did do a valve adjustment after it did this for awhile, dunno if that's what was "arrai" or not, but I have not experienced it since.

FYI, I rebuilt the engine over the Winter, just for "sport"...I have one event on it and no sputtering so far.

SO, what does this mean?? ...I guess it's possible a valve adjustment cured my woes?

Certainly, check your distributor belt, then maybe your plug (ignition) wires, etc.

BTW, just crossed my mind that when I did a valve adjustment, I had the engine out and also replaced the plug wires...so that is another (expensive) thing to consider!

Myles

When I first bought my car I had a miss or hesitation at 3,500+/- and again at 5,000 under acceleration. It turned out to be a bad O2 sensor. This is easy to test, simply unplug the sensor and drive the car. The plug is just above the engine tin on the driverside. With the blower motor in it is a little difficult to reach, but not impossible. If the problem goes away while unplugged, order a new sensor.

Myles

Ade - C4 91

Hi Steve,

O2 sensor is the obvious one as Myles said, but this fault could also be caused by a number of failing components.

The possibility of an air leak can be easly eliminated by your mechanic with pressure testing equipment.

Incidentally I'd take a look at the Coils and HT Leads, as both are problem areas when mileage gets higher and could cause the type flat spot behaviour you mentioned. Then take a look at the earth straps, especially Engine/transmission earth and the battery.

Good luck

Ade.

Ade

sullivs

Thank you, axl911, Piers, Jeff, Miles and Ade. Now I know what to spend my $100 Porsche Gift Cert on.

Steve