goody944

Hi all -

When I get the revs up really high (either from a stop or after passing another car), then settle to 'cruise mode', the engine seems to miss out quite badly for a while. If I let the engine idle (neutral or clutch in) the engine will die! This happens for a short time, perhaps within a mile or so or after shutting the engine off, then starting it back up, it returns to normal.

Just seems right after high revs, the engine misses out. I searched the posts but didn't see anything similar. Any suggestions where to start? I have no idea if it's DME, plug wires, or as simple as fuel injector cleaner is needed.

Thoughts??

TIA

Goody

Yabo

Well.. i dont know. i wouldnt bet on it.. but perhaps funky gas? maybe run some of that through, as well as fuel injector cleaner. Seems like somethig like that, if it goes away. Although. maybe its flooding itself so bad taht it dies out and then you have to wait till the gas evaporates before it runs correctly? those are my only guesses without understanding fuel delivery and such of this car too well yet.

goody944

Does act like it floods itself a bit. As far as bad gas- it's done this for a few tanks at this point. What do you all check when it comes to the engine missing out like this? It starts great, runs great until I hit the gas pretty hard -- then it runs like it's got water in the fuel!

Help!

goody944

still needing suggestions...BUMP!

chuckster

You might want to check for vacuum leaks. This would not explain why it runs fine until you take the engine to the high end. But a lot of times if a car misses at low RPMS but runs ok at the high end, it can be a vacuum leak.

Good Luck

Chuckster

Bryan

I'm also liking the vacuum leak idea.

When you rev the engine way up, two things are happening. First, the manifold vacuum is very low because the throttle is wide open. So vacuum leaks are not doing much because the difference in air pressure inside the manifold vs. outside is low. Second, since the throttle is wide open, the car is following a pre-programmed fuel curve and not using the input from the O2 sensor.

When you get off the gas, the manifold vacuum jumps way up because the throttle plate is now mostly closed. So now the vacuum leaks are letting in all kinds of unmetered air. But for some reason, the engine isn't going back into "closed loop" (using the O2 sensor signal) right away. So without the ability to compensate for this extra air, the engine sputters and coughs and can quit. After doing this for a little while, it suddenly goes back into closed loop and it's fine again.

Where my theory falls apart is that you said the car starts fine. Usually vacuum leaks cause rough running right after you start a cold engine. Because you have high manifold vacuum at idle and no O2 sensor compensation yet.

So you may have a couple problems here. One being some pretty significant vacuum leaks. It takes a pretty big air leak to stall an engine. Another being a nearly dead temp sender for the ECU that prevents the engine from going closed-loop until the engine is really hot. And then an idle mix that's been cranked rich enough to compensate for the air leaks at cold start.

Pretty complex theory, but I'm stickin' with it!

Bryan

nine-44

Mine does this also. It does it only when cold and only if I run it near or to the revlimiter. I don't make a habit of bouncing red on a cold engine, but it does it every single time I bounce red while cold. After a few mins of light throttle it cleans up and runs fine. It does not do it when up to temp either. I'm thinking either old spark plugs not firing good and loading up when the O2 is still not up to temp( running rich) or a weak ground to the DME. The DME idea, I'm thinking it's overheating the ignition or fuel board and cutting out. It runs on 3 and still idles with a flat miss. I'm doing the plugs soon, we'll see if that does it?

ilikemy944

wires? Though that might make it more of a constant problem.

ewainwright

You've got your work cut out. I agree with the spark plugs and wires. When I had a vacuum leak Baby ran horrid period. If you haven't done a tune up in a while start there and work your way into the vacuum mess. Dave at Lindsey has a nice kit and he sends it with a diagram. While your there address the idler hoses, engine breather, CV (if you haven't tossed it - you should) and those pesky coolant hoses. ed

goody944

Thanks for all the ideas... Bryan, I appreciate the detailed explanation. Have a couple questions, maybe more as I think about it a bit:

Which plugs do you guys like?
What do I look for in good plug wires?

JLeake

You may want to check your fuel pressure regulator. Also if you don't have a pressure guage on the end of your fuel rail yet, you may want to add one for about $12 using parts from a plumbing supply house. Helps a lot with diagnosing problems.

billybones

new fuel filter helped mine,,, did the same thing in cold weather.. no one changes these...If it is original it will be full of gunk...

goody944

Billybones good point ... I changed it shortly after buying it last year.

BTW, how do I get 'Rennlist Member' to show under my name? And yes, I've joined already...

goody944

Well, first thing I've tried is STP Fuel Injector cleaner (red bottle, $3 @ AutoZone), and only about 20 miles and it's obviously feeling better. I'll finish this tank, run another through, and I should be in good shape.

Thanks for all your help! A tune up is still in order.

Peckster

Are you hitting the rev limiter before it happens? Maybe it takes a while to shut off?

On another topic, I don't think I've ever hit redline with a cold engine. Not a good idea.