Help!! Car is breaking up at 5600 rpms?
 

Im stumped on what is going on and need some help to narrow down or even suggest some new ideas on what to do.

The car drives fine and runs perfect during normal driving but when i try to do a WOT run the car acts like it's hitting the rev limiter at 5600 rpms but it's more of a engine break up??? The car will bang out or cut out at 5600 rpms until i let up off the gas then shift out. The tranny has about 3,000 miles (4L60E) and the tuning is through Ed Wright (6400 rpm shift points and 6800 rpms rev limiter).

Tranny builder says that if it's transmission related it would happen at part throttle and not just WOT and by now i would have lost the clutches and bands if it were related to them. The car shifts sharp and locks up perfect with no drag on the tranny. He told me i might want to question my valve springs (20K 918s) because if they have taken alot of abuse they might be getting weak and causing the valves to float?

I called Ed Wright and he told me that there is no way i lost my revlimiter or it moved down on it's own and is probably ignition related. Told me to run down a burnt wire or replace them and to ditch the NGK TR6s for Autolite 104s? Says they have had problems in the past of the same situation and found that the Autolites cured it up. I have been running the TR6s for 3 years with no problems and find it hard to believe that it's related to the plugs?

As of now im being pulled in 20 directions on where to look. All my Random misfire codes have been deleted by Ed so i won't pick up a SES light due to that problem. Here is what i have done so far.

A taped the Tranny temps (181-186 degrees Hot)

Engine breaking up at 5,604 rpms in 1-2nd shift and 2nd-3rd shift through A tap

Changed plug wires,did not work

Checked for broken valve springs,none were broken

Checked tranny fluid level to make sure it was not low or high

Anyone had this problem please help me track it down or atleast give me some pointers on other things if im heading in the wrong directions. Tomorrow i will A tap each cylinder and inspect the plugs to see what is going on.


Scott

Re: Help!! Car is breaking up at 5600 rpms?
 

Could be a fuel pump that is on it's way out and lost some line pressure.

Re: Help!! Car is breaking up at 5600 rpms?
 

ttt

Re: Help!! Car is breaking up at 5600 rpms?
 

I would take a look at the spark plugs next.

Re: Help!! Car is breaking up at 5600 rpms?
 

Autotap has a current misfire by cylinder tracking which works even if the random misfire SES light has been switched off. Have you tried that?

Re: Help!! Car is breaking up at 5600 rpms?
 

Ragtop,were going to try that today but i think im dead set on what is the problem. I talked to Paul at Thunder racing and we both think that the 918s valve springs are probably shot and causing valve float but he suggested to A tap the fuel to see if that might be a culprit.

These 918s are the first batch made and if im correct i was one of the first 5 cars to try them lol and they have around 25-30K hard miles on them after i sat down and thought up how long they have been on the car. I'll find out more tonight when i finish up the A tap log.

Scott

Re: Help!! Car is breaking up at 5600 rpms?
 

Why is no-one suggesting knock retard when this sounds like a textbook case? Did I miss something in the another post, or in the troubleshooting history?

Re: Help!! Car is breaking up at 5600 rpms?
 

Since he Atapped it you would think he would have noticed any KR, but maybe not?

Re: Help!! Car is breaking up at 5600 rpms?
 

mine started to break up around 5600-6000 rpms once, but I was told it was from where the car was running lrean perhaps on those areas. Just food for thought.... I'd check the a/f aorund there just to be safe. But it could be those springs needing to be swapped also;) good luck man!

Re: Help!! Car is breaking up at 5600 rpms?
 

when you are driving and slowly take it up and hold it at 5600 does it break up?

Re: Help!! Car is breaking up at 5600 rpms?
 

Your not going to beat me like that......



hope you get it fixed man.

Re: Help!! Car is breaking up at 5600 rpms?
 

Check fuel pressure to make sure it doesn't drop at WOT in that RPM range and maybe try another's MAF sensor.

Re: Help!! Car is breaking up at 5600 rpms?
 

Sounds like weak valve springs

Re: Help!! Car is breaking up at 5600 rpms?
 

Mine shakes or whatever...you can feel it at 5800 and they said my car is limited in first gear to 5800...not in the others though...never hit limiter going to about 6200 in 3rd. Anyway they said mine is 5800 in first, maybe your just shafted and yours is 5600.

Re: Help!! Car is breaking up at 5600 rpms?
 

I'd check the fuel pressure first, and then check the valve spring pressure. Any engine shop should be able to check the pressure for you. I find it hard to believe that the B1 wore those springs out that fast, but I guess its possible. I know there were some problems with the early 918s. I had the early 915s and they had about 30k on them before I got rid of them and they were still holding back a Comp XE grind. It sure doesnt sound rev limiter related to me.

Re: Help!! Car is breaking up at 5600 rpms?
 

I remember seeing a post that the factory tach is slow, expecially in the lower gears. you could very well be hitting the rev limiter. I have the same problem. I shift at 5k 1st, then 5.5k second, then 6k 3rd. My et's are actually better if I shift like that. So I'm betting the tach is slow. I have 4.10 gears so my revs really shoot up fast.