Chris;

Surprised that you haven't gotten any responses on this.
First time I've ever heard of a rev limiter built into the computer. But it would make a heck of a lot of sense.
I'd like to know the answer also.
Maybe this response will bring it back to the top and someone will see it and give us an answer.
If not, maybe you can kick it to one of the experts and see if you have any better luck.

 

Larry - I don't know about the A9P, but the stock A9L has a 6250 rev limiter built in. However, it works by stopping the flow of fuel to the engine which results in a lean burn. This is Bad! Even worse in blown or turbo'd engines. If you plan on getting into that rpm range, there is a chip available called a rev limiter extender, however unless you have a mill strong enough to spin in those dizzy heights, you will break the engine. Better bet is to put an MSD6al ingnition in. You can set the rev limiter on it via different plug in "pills." The MSD limits spark to various cylinders, but no single cylinder twice in a row. That way there is no lean burn and by firing off the "dead" cylinder the second time, there is spark plug fouling either.

We have our MSD set to 6000 and the shift light to 5800. Works like a champ.

Frank n Sons.

 

The neat thing about the rev setup on the MSD is it regulates power to various cylinders and on the next rev pass goes to another set, so loading is not a problem.

You can buy rev limiter chips in increments of 100 now, 6100, 6200, etc. which is a neat touch.

JQ

 

I already have the MSD6AL, but this info is just to settle a discussion among some Mustang guys. I am in the process of putting together a forged 347 and I dont want to go past the 6250 anyway, in fact I will be using the 6000 chip, my set up (heads, cam, intake)is to make all my HP/T by 6000 or just beyond.

 

I understand that only the standard shift trans has a rev limiter. I dont like the stock rev limiter because when you hit it, it sounds like you have blown the engine when it shuts off the fuel.
Bill Rodman

 

Actually, there is NO REV limiter built into any Ford's 5.0 computers. Way back when the 5.0's were new, we would modify them and run them way up past 6250 with no computer or EEC mods. There was no computer mods at the time to be had!!!(1989). The 6250 MYTH started because the stock roller lifters and stock valve springs couldn't stand any more RPM's than that and would float the valves somewhere around that RPM. It sounded terrible, and to some it seemed the computer turned the engine off. NOT SO. Only GM cars had rev limiters at that time, I rode in a Camaro that would LITTERALLY SHUT OFF FOR 3 SECONDS at 109 MPH at OPEN track at Watkins Glen. But the Mustangs would go as far as the mechanical limit of the engines. THEY NEVER SHUT OFF. SO IN ANSWER TO ALL OF YOU, THERE IS NO REV LIMITER of any kind IN ANY EEC 4 Computer. PERIOD. They will run right up to 10,000 if you can spin the mechanical assembly that fast. I've done it. STEVE SIEGEL

 

Originally posted by Steve Siegel:
SO IN ANSWER TO ALL OF YOU, THERE IS NO REV LIMITER of any kind IN ANY EEC 4 Computer. PERIOD. They will run right up to 10,000 if you can spin the mechanical assembly that fast.

That's FUNNY! Total BS, but funny.

 

Originally posted by svobud:
</font><blockquote>quote:</font><hr />Originally posted by Steve Siegel:
SO IN ANSWER TO ALL OF YOU, THERE IS NO REV LIMITER of any kind IN ANY EEC 4 Computer. PERIOD. They will run right up to 10,000 if you can spin the mechanical assembly that fast.

That's FUNNY! Total BS, but funny. </font>[/QUOTE]It's not even funny, but it is total b.s.

 

Chris,

When I had my stock tach in my mustang, it went up to 7000+ rpm numerous times. When I put a good tach in the FFR (same computer/motor), 6250 was it. I have heard this from many others. The factory tachs are either garbage or Ford wanted them to show high readings on purpose.

Dave

 

I sure hit something one day in the high rpms. Thought it was the rev limiter. Hope it wasn't something else. Car runs fine, tach is not accurate so really didn't know how high I was (rpm wise that is!)

 

With my SW tach, somewhere between 6200 and 6500 rpm things start to sound really bad. I've only hit it twice, but there is no doubt about what's going on.

 

I have asked the same questions over on the Corral forum with the exact same answers. Anyone have any actual facts to back it up? If they dont have a limiter, why does Ford Motorsport sell an rpm extender?

 

My problem with what Steve is saying is that in the Ford Manuals I have here, it says

The control module is designed to give you performance, economy, drivability, emission control, and more. It provides air/fuel ratios to prevent destructive detonation, and limits engine speed to 6250 rpm to help prevent other kinds of damage

It goes on to talk about the SVO Extender and Fords SVO Extreme Performance Engine Control System. All of which it states will now allow you to go past the limits of the stock control unit to the point of destroying your engine.

So on my Crane unit I have it set for 5500 rpm - little dials on the end of it allow me to make the changes without having to buy a different chip like the MSD system. That way if I miss a shift I hope to still have a working engine!

 

Ralph, did you come across anything about the A9P? that is the computer I am trying to find out about as I have heard that it doesnt have a rev control, any sources out there/ I have a couple of publications for Ford EFI, but I couldnt find anything for this application.

 

I'll look through my manuals but they seem to be saying that all the control units are programed the same way for all mass air systems at least.

I'll keep looking. Way back... I bought all the Ford Shop manuals for the year donor I have, wiring diagrams, EFI manuals, all the tech notes, in short everything I could get! Now I see that they are out of print and difficult to get.

 

Something for an EEC ref that I cam across - not gospel but ....
================================
Speed Limiters
ROM addr : Data
0x7A86 : FF
0x7A87 : FF
0x7A88 : FF
0x7A89 : FF
There are two speed limiters here, and an ON and OFF value (With hysteresis, I
think. Which means once you hit the speed limiter you need to slow down to the off
value before you can accelerate again)
When data = FF the speed limiter is off, otherwise the conversion is as follows:
0FFH --> 255, then divide by 2 and you get 127.5
Not sure which is on and which is off. Maybe someone else can help.
I think it’s
Speed Limiter A: 0x7A86 ON; 0x7A87 OFF
Speed Limiter B: 0x7A88 ON; 0x7A89 OFF
The ONs and OFFs may be swapped!
Rev Limiter
Max RPMs seems to be PIP filter related! Any thoughts here? Please post your ideas
to the EEC group.
At address 0x7C16 I have for data C103 (reverse bytes to get hi-byte first, 03C1).
H03C1 --> D961 which I think is the PIP filter. When I cut that number in half, my
rev limit is half, so it definitely affects the rev limit.
=======================
Souce is:
TECHNICAL NOTES ON THE EEC-IV MCU
INTRODUCTION
Compiled by Tom Cloud <cloud@peaches.ph.utexas.edu>
(font is Courier New)
DISCLAIMER
(The information supplied herein was taken from technical and sales literature, e-mail
archives, news groups, and wherever else it could be found. If it helps you,
great! Please return the favor by sharing what you learn with me and others.)
None of this data is guaranteed accurate! USE AT YOUR OWN RISK! It is a collection
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=============
To me that seems to say thare is rev limit logic - if changing a value in the static memory changes the point where it starts cutting out. Sorry but writing for realtime control circuits was a long time ago. I can read and kind of understand but to do it ... not anymore.

Hope this helps...

 

Guys,
I had an 86 mustang stick 5.0. I hit the rev limiter or whatever it was at 6400 RPMs all the time. If it wasn't a rev limiter I'm sure that I would have BLOWN it to pieces! It still was running good at 60,000 miles when I traded it.
Thanks,
Ron FFR1738