Can't quite reach redline under load...

[dtfastbear]

Since getting my engine rebuilt (top end only) a few months back, our '86 euro 3.2 won't quite get to redline under load on the track.

In 2nd, 3rd and 4th (the only gears we use and approach redline on...) the engine will start to stumble and "break up" at about 5800 rpms instead of the expected 6300.

It doesn't feel like a rev-limiter kicking in too early, as the stumble is not as clean as hitting the rev-limiter.

Any ideas? This certainly sounds and feels ignition related. Could something be misadjusted since the rebuild - or just old, nasty ignition wires...

Thoughts?

Dean

[masraum]

Hmm, could be ignition, but my thought would be fuel, either way, I would check it out since it's probably not good. If it's fuel related then its probably lean which isn't good. Hopefully it'll be a loose connection or something. Good luck.

[Rot 911]

Will it hit redline in neutral? If so it is probably fuel related. If not, probably your rev limiter.

[dtfastbear]

Yes, it will. Creeping up to redline, it'll cut out at the proper redline. Stabbing the throttle adequately in neutral will wind the motor past redline briefly, like you'd expect.

Fuel pump? Fuel filter? We just had all the injectors cleaned and matched for flow at the time of the rebuild, too, so I sure hope that's not the problem. But that does mean that the entire fuel system was apart if they removed all the injectors individually to clean and test them, so something could have gone back together slightly wrong.

Any more specific ideas about where to look?

Thanks!

Dean

[Plavan]

My Dad had the same problem with his race motor. He could not get it over 6500rpm and the temp was fine. He was down on HP too. What happened is that a bearing started to go. I would check your oil/oil filter for metal bits. I know this may sound a little extreme, but we never thought a bearing would be going either. The motor siezed up. We were thinking it was an ignition/MSD/fuel problem.... but it was to late

Hopefully yours is a ignition problem.

[Early_S_Man]

Seems more likely to be a fuel filter than the pump, but you can test pump output quantity in 30 seconds and compare to the value in the spec book ...

You can't really assume that the fuel filter has been changed ...

[RSupdate]

JC Plavan ...

Interesting, if not scary post....as I have to admit my 3.2 is suffering from the same problem, although intermittantly

engine will be out this week due to a broken 3rd dog gear.....

how does one check for a bad bearing(s) short of splitting the case? granted an oil sample analysis could detect metal fragments...I change my oil about 6x a year, probably negligable amounts of any metal unless it's really bad.

Not doubting or contradicting...but I'm trying to make the connection b'tween the bad bearing (a mechanical problem) and the cutting out (elrctrical/fuel/timing?) at/near redline.

any help for my thick brain is appreciated

[RSupdate]

Originally posted by Early_S_Man
Seems more likely to be a fuel filter than the pump, but you can test pump output quantity in 30 seconds and compare to the value in the spec book ...

You can't really assume that the fuel filter has been changed ...

Thx Early S man.... looks like we posted at the same time.

good thought... but I have new fuel pump, fuel filter, DME...etc...

gracias!!

[Vintage911Racer]

Mine used to do something similar. Check the distributor. My bushings were shot inside. Once I got that fixed, no problems.

www.motoparts.com did the work. Great, Fast service.

[dtfastbear]

Please, please someone find a way to help me believe that it CAN'T be the bearings!!!! AHHHHH!!!!

Seriously, though, I'm due to change the oil between track events this week anyway, so I'll hold my breath and take a look at the oil plug for metal.

[RSupdate]

Originally posted by Vintage911Racer
Mine used to do something similar. Check the distributor. My bushings were shot inside. Once I got that fixed, no problems.

www.motoparts.com did the work. Great, Fast service.

ah-haa.... now This makes sense to me..... interesting enough to check out for sure!!!!

dtfastbear..... we are both hoping (actually - praying..) that the main bearings are NOT the culprits here...if it is we are both going to a.) miss a few track days and b.) be very poor for awhile..!!!

you cross your fingers for me & I'll do the same for you !!!!

[dtfastbear]

Mutual positive kharma, indeed, Johnny!! My wife and I are looking for a house right now, so if this means a new bottom end, we're done for the year...

I'm even more anxious to find an ignition/fuel source to let me rest a little more easy.

Cheers,

Dean, with fingers crossed.

[Vintage911Racer]

DTFASTBEAR.

Sorry to use your thread for a shmeless plug. but I work for a mortgage company. www.bankersexpressmortgage.com.

We all race here. When you are ready, give me a call and we can get you all taken care of. Or just call me if you have any questions about the purchase or your car.

888 845-8888 Ext 243

Mark Scott

[dtfastbear]

Mark,

No problem with the "shameless plug". I'll give you call later today. I have some mortgage questions that I'm sure you can answer, and I'm happy to give you a shot at our business, too.

Thanks,

Dean

[dtfastbear]

Problem solved!

Even after we found a cracked distributor cap (replaced it) and a bad plug connector on one cylinder (replaced it), the problem was still there.

It turned out to be a slightlly misadjusted speed sensor on the crankshaft. Apparently, the gap between the sensor and the teeth it uses to measure crank speed is super-critical (0.8mm). We adjusted it to the right gap, and NOW the car is running GREAT!

Thanks for all your suggestions along the way...

Dean

[RSupdate]

Hey that's great news!!!

[Mark McClure]

How did you go from looking at the ignition system to the speed sensor?

[moazam]

Originally posted by dtfastbear
Problem solved!

Perfect! Now you can look forward to only dealing with the mortgage stuff.

[dtfastbear]

No credit (or blame) goes to me, and I'd have to ask my mechanic how the thought process went. However, once he told me what the cause was, I opened up my 911 Bentley manual to read about the speed sensor. Sure enough, it says right there, "if the car breaks up at a certain RPM, a mis-adjusted speed sensor can be the cause".

I guess the speed sensor is one of the inputs to the computer. Once they determined that it wasn't the computer, they had to see where it was getting bad information...

Dean

[Vintage911Racer]

Are you still looking for a loan????

give me a call

888 845-8888 Ext 243