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Discussion Starter #1
Ok. My car feels as if it is hitting rev limiter at about 5300/5400 rpm. It has done this for a long time, and it always does it at the same rpm. I have changed everything. Here is a list of everything that I have replaced, or changed with my friends car to see if that was the problem. We methodically changed one thing, checked to see if the problem was solved, then went on to the next thing. The list is as follows:

New Holley Ignition Box, with new Holley coil
New MSD Distributor, New TFI
New cap/rotor/wires/plugs
Swapped Computer with another A9L
Tried removing spout connector, still have problem
New O2 sensors

Upgraded alternator to a 3g.

New Battery Ground cable
New Fuel Pump and Fuel filter.

We have changed or checked ALL of the ignition components. This problem has happened with different distributors, different coils, and different ignition boxes(as well as stock ignition). We have swapped all the aforementioned things and none of it has made a single difference. The car falls on its face at 53/5400 rpm and if I keep my foot into the throttle, it won't accelerate past this rpm. This RPM is on an autometer tach, so we know it is accurate(not really 6250 rpm). The holley box rev limiter is set to 7000 as well.

Since we concluded that all of the ignition hard parts were not the issue, we went on to the fuel system and tried changing the fuel pump. This was not it. The regulator probably has 8000 miles, and the injectors less than that. Regulator is a Kirban, injectors are FMS 30#. FP is 40 w/o vacuum hooked up. Timing is 16 initial.


The car runs great otherwise. It just falls on it's face at that rpm.
We have been racking our brains and we can't figure this out. I just stepped up to ported TW heads/intake and a custom cam so I am leaving a lot of power on the table. I need to get this figured out. Does anybody have any idea??????
 

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My supercharged Cobra did the same thing. Turns out it was my Pro-M meter. Swaped it out and the car ran fine. Maybe you could borrow one to check.

Bill
 

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Have you checked your valve train. You could be floating your valves. 5300 RPM sounds kind of low for valve float even in a stocker but you never know. Sounds like you covered everything else. Its worth checking if all else fails. Good luck.
 

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Discussion Starter #4
The meter is a brand new C&L cal'd with the 30# sample tube. I had a Pro-M 80 before the C&L and had the same problem even with that MAF. I switched to the C&L because it was easier to mount inside the fender than the larger Pro-M 80 that I had before.

I thought briefly about valve float as being a possibility also, but the TW heads I have have upgraded dual coil valve springs rated at .600 lift. They were upgraded when I bought the heads from Total Engine Airflow early last year. These springs should withstand a heck of a lot more abuse than 5400 rpm, but I'm going to keep that open as a possibility, although it seems to be on the outer realm. :(
 

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Kieth:

What's your fuel pressure like under load? Didn't see where you posted that.
 

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MY CAR DOES THE SAME THING. I'm pretty sure its the fuel pump. Your motor is prolly just sucking it dry.
 

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Discussion Starter #8 (Edited)
Gray - FP under load looks ok. I have 40# static pressure with vacuum disconnected, and when the problem occurs my FP fluctuates slightly around 35 psi. Other than that, FP increases on throttle and looks to be ok. If I remove vacuum and plug the line, the FP stays right at 40 lbs even when the problem occurs.

red - Cam is a custom grind from Comp Cams Extreme line. It's installed straight up as per reccomendation. This was also happening with my Stage 1 cam last year. I'm positive the cam is in correctly even though I did not degree it. Lift is .530 on intake and exhaust so the springs should be more than tough enough to handle that lift.

Pearl - We installed a brand new 255 BBK pump in the car last night to replace my 4 year old 190 pump. We thought that it could have been the pump also and decided to change it. Didn't help at all. :(


One thing I forgot to mention up top is that I can crerate this problem just by revving the motor to 5400rpm in neutral. The car does not have to be under load going down the street. I can create it in my driveway with the vacuum line connected to or disconnected and plugged from the FPR. :(

ANother thing.......On the dyno last year, with my old combo (non ported heads, non ported intake, Crane HI-6S ignition, MSD Blaster coil, Stage 1 cam), the car would go very lean right at 5400rpm when the problem would arrise. We had to cut every run off at 5400rpm due to the lean condition.
 

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Sounds like you are hitting your factory limiter, even if you aren't really reaching 6250 RPMs. You said yourself, it will do it in gear or in neutral, and that the runs were aborted after it went lean on the dyno. Try swapping your computer with another one. Could be something to do with it. Just a thought. Everything else; fuel, air, valvetrain, ignition, seems to be in good shape.
 

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Put a vacuum gauge on the car and watch what happens when the car falls on its face. If the vacuum is going down when your problem occurs, you probably have a partially clogged exhaust system.
 

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Discussion Starter #11 (Edited)
Erik - We swapped A9L EECs yesterday. Saul (Grntrnk on COrral) came by and we tried swapping his EEc for mine. My A9L in his car did not produce the problem and his A9L in my car still had the problem. Unless it's a wiring problem to/from the EEC, than it's not the computer. Wiring is possible, but only at 5400rpm everytime? Highly unlikely I would think.... :(

Don - That's a good idea. Where would be the best spot to install the vacuum gauge that would give me a good reading while I tried it out? The headers are brand new BBK 1 3/4" LTs with a matching new BBK off-road shorty H. The cat-back is the same one I've had for about 4 years. A MAC Flowpath 2.5". I did have a set of cats explode in my Bassani X when I had it, so it's entirely possible I have something lodged in one of the baffles. I removed the cat-back after the blow out to check, but I only did a visual. Something could have gotten lodged in there that I wouldn;t be able to see or hear......
 

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Discussion Starter #12
Ok, got some vacuum readings a few minutes ago....

At idle, I have 12-14" of vacuum. Small fluctuations between the 2 due to the cam. Looks good. Start getting into the throttle and vacuum goes up steadily. Looks ok. I brought the rpms up to 5100 and I had 25" on the gauge. As soon as I went a tad further to 5300/55400, the gauge dropped like a rock right to 14" of vacuum. I did it twice with the same result both times. Vacuum goes right to 14" from 25 right at the trouble RPM.

Whatcha think??
 

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i had this problem last year and changed everything on that you did.
i called rick anderson at anderson ford motorsport and he told me to gap my plugs @ 28.
i thougt he was cracked in the head but did it and i couldnt beleive it. i spent about 500 bucks and it turned out to plug gaps.
give it a try if you havent already, it worked for me.
http://home.talkcity.com/SparkplugSt/igivjiz/
 

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Keith, if I understand correctly, you indicate that this problem happens at the EXACT same RPM every time? Or that you cannot exceed 5400 RPM no matter what?

Just so I understand- answer a few questions?

If you keep the motor reving just BELOW the threshold of where the problem is, will it stay running ok? In other words, with a load on the motor, if you ran it up to say 5200 RPM and did not decrase or increase RPM for a period of time, will the engine keep running strong? Does it only do this if you run right up to that problem RPM in one constant rev?

Could there be something in the fuel system acting like a "check valve" of sorts? In other words, when you reach the RPM level where the problem is, is it possible that the fuel system is somehow obstructed in some way? Do you understand what I'm getting at here? Perhaps something is clogging the return line or the intake to the pressure line at some point? Sounds far-fetched but you seem to have tried everything else short of putting your entire engine in another vehicle...

I wonder if there is perhaps a problem with your fuel pressure regulator? I see you mention the regulator has 8000 miles, but you don't say if you have changed it or not.
I get the feeling it's related to the regulator Keith, or something in the fuel system that is screwing up. You also mention new fuel pump and filter, but what about the fuel pickup?

I hope you get it figured out, but one other thing- free-reving the engine into the upper RPM ranges without a load on it is not something you want to do with any regularity. It's better to have a load on the engine.
 

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Discussion Starter #15 (Edited)
Pimpt - If I get out of the rain this weekend, I'll give that a shot. Right now the plugs are gapped at .54......

Greg - The car runs absolutely fine until that one point. It revs happily and freely up to about 5300-5400rpm and then it will absolutely go no farther than that. I've held my foot to the floor during road testing for a few extended seconds in 2nd and 3rd gear and the car will not go above 5300-5400 rpm. It'll just sit there and give me an erratic rpm reading right in that area. Very similar to a rev limiter.

When we replaced the pump, we looked at the entire pickup assy and it looked ok. It has some rusting on it common to any New England car, but it didn't look like it had any kinks or anything that would otherwise cause me concern. We replaced everythng inside the tank except for the pickup itself. New pump, sock, rubber hosing to pickup, the works. The lines all look ok coming to and from the pump. Unless there is something internal to one of the lines that I can't see, then the outside visual check looks ok on those.

The regulator is a Kirban that I bought shortly after I bought the car back in 98. It hasn't been changed since then. I may just get a regulator anyways since it's pretty cheap to replace. The last thing we had on our list of possibles was the regulator. During road testing, we paid particular attention to FP measured on my Autometer gauge. At the trouble spot, FP is in the 30-34# range with an erratic needle at the trouble zone. The needle bounces around right in the 30-35# area but does not fall or go above that with my foot planted and the car hitting the zone.

I got a decent idea from Don a few posts below this and he mentioned checking vacuum. I checked it with the results you see a few replies below this. I pulled the cat-back to see if that may have been causing a restriction and that wasn't the case. Car still hit the trouble spot at 5300-5400. Vacuum at 5200 is steady at 25" or so, then drops like a rock to about 14" when it hits that zone.
 

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I'm going to venture a guess that your problem is related to the AFPR. Give it a try dude, you have nothing to lose at this point.

/me has visions of Keith swapping his entire engine into another car :eek: :eek:
 

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Discussion Starter #17
/me has visions of Keith swapping his entire engine into another car :eek: :eek:
Man, I hope it doesn't come to that!! :(

I'm going to order a new FPR this weekend and toss it in next week to see if that does it. I have to pull the intake to do it easily so I might as well order my 1.7 roller rockers too and toss them on the intake side. :) Neil reccomended I run 1.7 intake and 1.6 exhaust for a total output of about .570 intake and .530 exhaust lift with the cam he specc'd for me.

I'm hoping the FPR does the trick. I've had this problem since early last year and it's been quite tiring trying to figure it out. The sad thing is, I've run [email protected] WITH this problem! :):)


Wish me luck dude!!
 

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Good luck man, I'm very interested to know how this turns out!
Wish me luck in return! Time Stockwell from Fox Lake called and my motor is all done, just waiting for custom length pushrods and it's go time...!
 

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Discussion Starter #19
Awesome dude! Good luck to you too then! You better throw a post up so we can see how it runs!!

Once I get a chance to try a new regulator, you'll see this post back at the top......good or bad!! :)
 

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:curses: AHHHHH! this is worse than a soap opera.....I cant wait to find out what happens next!
who shot the RPM?? was it the gap or the regulator?? stay tuned

:rolleyes: sorry it is late..........................what is a good gap anyway?
 
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