Miss at 6000 RPM

Pokageek · Aug 1, 2007

Fuel filters should be changed once per year generally speaking but you dont drive your car that many miles per year..still not a bad idea.

1slow95 · Aug 24, 2007

I just changed the distributor and that didn't help. I got a fuel filter I'll put on tomorrow or sunday when I'm under the car working on the rear end. I doubt that will fix the problem, so what's next?

Could it be the computer or my chip gone bad? I was having problems with the car revving itself and shutting off randomly about the time this problem started. I cleaned the contacts on the chip and that helped for a while, then it came back, then it mysteriously went away.

I need to have this fixed by next friday for NMRA!!

Pokageek · Aug 24, 2007

I had this issue with the tweecer. That chip for some reason just would not make good contact and it would revv up and then shut down. Used to drive me nuts.

1slow95 · Aug 25, 2007

I tried to get a video of what it's doing, but it didn't turn out great.

http://www.mustangaddiction.com/movies/6kmiss.wmv

I think I'm going to order an adjustable FPR and fuel pressure gauge on monday. What gauge would I need to for the schrader valve on the fuel rail?

Edit: Will this work on our cars? http://store.summitracing.com/partd...=SUN-CP7818&N=700+4294839567+115&autoview=sku

Red1990Lx · Aug 25, 2007

Have you checked your plugs and wires to see if they are fouled or gapped incorrectly? Its the small things that tend to haunt us and it seems like you have checked/replaced just about all of the common problem areas...

1slow95 · Aug 28, 2007

I made some progress tonight. I installed the Aeromotive AFPR at 45psi(stock was 42), but that did almost nothing. So tried one more time unplugging my Crane ignition and using the stock ignition. Success!!....Almost. It still has a nasty pop/miss at 5800-6100, but it only does it 2-4 times and it's mostly smooth past 6k. Since this did not cure it completely, I'm thinking maybe my Crane box isn't bad...Is it possible the plugs/wires are at a point where they can mostly handle the stock current, but the extra voltage from the aftermarket box is too much?? My plugs are practically new, but I've had them out a couple times and dropped them several times. With how cheap a set of plugs are, I'm just going to pick up a new set tomorrow and try them out.

If it turns out to be the plug wires I will be pissed. A $100 set of wires should last more than 6 months!

Redsnk95 · Aug 28, 2007

Did you change the fuel filter yet? Sounds like a fuel problem. The crane box can go bad I had one that would work and not work intermintently.

1slow95 · Aug 28, 2007

Yep, changed the fuel filter.

IMO, the fact that it still does it when bypassing the crane ignition, even though it's not nearly as bad, tells me something is still wrong. Somebody mentioned once that a cracked spark plug would always miss at the same rpm every time, which is what it's doing. It used to be kind of intermittent, but lately it's been very consistent at just over 5800 rpm.

94 Cobra 5.0 · Aug 29, 2007

Had a similar problem that you have been describing. On mine (stock for the most part) I had a above 4000 rpm. The cap rotor wires and plugs were just over a year old. Had bosch platinums in the car and kept having the misfire. Changed the bosch's out for champion plugs and a new stock coil and havent had a problem with it since. Dont know why it was having a problem with those plugs but my car doesnt like them. Might help might not hope you get this problem figured out. Matt

HISSIN50 · Aug 29, 2007

94 Cobra 5.0 said:
Dont know why it was having a problem with those plugs but my car doesnt like them. Might help might not hope you get this problem figured out. Matt

It's common for EFI 5.0s to not like platinum plugs. They don't conduct as well as copper plugs (but as a result, they last a long time with little gap erosion). The normal symptoms are the 4K RPM miss and sometimes a strange idle.

1slow95 · Aug 29, 2007

94 Cobra 5.0 said:
Had a similar problem that you have been describing. On mine (stock for the most part) I had a above 4000 rpm. The cap rotor wires and plugs were just over a year old. Had bosch platinums in the car and kept having the misfire. Changed the bosch's out for champion plugs and a new stock coil and havent had a problem with it since. Dont know why it was having a problem with those plugs but my car doesnt like them. Might help might not hope you get this problem figured out. Matt

My car runs great at all rpm's until it hits 5800. Plus it used to run right with these plugs, it was very smooth up to 6300 or so when I let up.

I have a set of AR3924 plugs on order, they'll be in tomorrow.

Zero_chance · Aug 29, 2007

A kid that worked with me at my dealership had a similar problem and it turned out to be his fuel pump. Dont know how he diagnosed it but he said he replaced it and it went away. He stil ldrives the car and was doing passes in True Street at the Fun Ford weekend last week so it must be good.

1slow95 · Aug 30, 2007

Well now I feel like a complete idiot. When I first mentioned this problem on here(6-8 months ago), somebody mentioned it could be the crane box going bad. I thought for sure I tried bypassing it, and it didn't help...but that could have been for a different problem I was having. Tonight after I changed the spark plugs and found a plug wire that wasn't on all the way it was still doing it. So I unplugged the rev limiter and set it to "00"(so it's turned off). Unless it's a fluke thing, it went right up to 6200 like nothing.

So now I have a choice, live without a rev limiter or replace the ignition box. Does Crane have any kind of warranty?

HISSIN50 · Aug 30, 2007

Good job Mike!

Miss at 6000 RPM

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