AJP 4.2 Flat spot @ 3k

[totalpetrolhead]

My car has started to develop a flat spot at 3000 revs on WOT. Car bogs down momentarily, then seems to clear and continue. It has felt slightly under-powered lately, either that or I'm getting used to it!

Initially thought it could be coil packs breaking down, but then have more of a feeling it is fuel related. I think compression is good, car starts from warm/hot no problem. There does seem to be gurgling from tank/pump/filter area, but only when ignition is energized again to start after car has been on a run up to temperature.

I will replace fuel filter for starters. Are there any venting issues anybody has experienced with the fuel tank?

Any other similar ailments anybody has experienced?

Does the speed sensor on the diff send a signal the ECU, or just the speedo?

Car is a sept '97 AJP 4.2 with 38,000 on the clock.

Cheers,

Steve.

[Boatbuoy]

Hi,

I can't solve the overall issue, but I can help with your question about the speed sensor. It's not connected in any way to the ECU, there is however a crank position sensor that works on the same toothed wheel principle on the flywheel. That is connected to the ECU.

Olly

[Luckyone]

It’s surprising how quickly you do get used to the power, I can still remember the first time I drove it some 12 years ago now I was shaking all over from fear & excitement. I did take a while to get used to it but once you have it seems like second nature. That is until you find yourself on full opposite just changing lanes on the motorway this time of year, at least that keeps the tailgaters off your back for a bit!

After a while though I often felt like it was really down on power, even took it to a few rolling road sessions but it was only 10BHP down on the average, so it couldn’t have lost that much. Its only when you’ve been driving other regular "fast" cars like new 325 BMs etc for a while then get back in the Cerb it seems like a rocket ship again the first time you put your foot down again, unfortunately the longer you had it the quicker that feeling wears off each time you come back to it.

That’s not to say there’s isn’t something wrong with yours, but it may be worth comparing to some others or getting it to rolling road to check before you spend too long looking for faults.

[morebeanz]

There is a fuel tank vent through a carbon filter that can get blocked and cause issues. Normally spotted if you run the fuel very low and get a sucking noise when you remove the fuel cap!

[totalpetrolhead]

Thanks for the replies so far guys.

The car is definitely not performing as it was, with a noticeable flat spot. I'm just about to head out into the garage to change the fuel filter - I'll see if that make any difference as the first port of call.

Glad to hear the speedo sensor isn't related in any way to the ECU. I'll pull the crank sensor and check for crud too.

Steve.