Rev Limiter on ZF5?

[Acgallen]

I have a 1993 A3M computer with a 5.0/ZF5 setup. I have finally gotten it able to drive on the road but have noticed when slowly stretching the RPM's out, the truck will cut out at around 4000-4500 RPM. By cut out, I mean it will buck and pop without going any faster. 1st gear I am able to go beyond 4k but it doesn't do much for me. Fresh built motor, but it seems to be running fairly rich with some exhaust pops and rumbles on downshifts. I talked to a guy who said with I would possibly need a tune to allow the transmission to go beyond 4k, but I'm not sure. Any suggestions are appreciated. I can provide video of it if that would help.

 

[Shran]

Transmission has nothing to do with your problem... guaranteed. I don't believe anything Ford from that era had a rev limiter of any sort.

So it's a new engine - what parts did you use in your top end? Possible that you've got a weak valve spring(s) and you're simply floating valves at high RPM? Running out of fuel, timing off just a bit, plugs/plug wires arcing out, bad coil, something poorly grounded...?

How did you determine that it's running rich? Exhaust pops especially going downhill and engine braking are sort of normal, some mufflers make it much more obvious - my F150 never did that with stock exhaust but the second I put duals and glass packs on it, it would pop when engine braking. Doesn't mean it's running rich, you would need to look at data from an exhaust sniffer or live data on a scan tool to confirm that.

 

[RonD]

A3M is for manual trans V8
Yes, 1993 shouldn't have REV limiter but if it did then REV limiters are 3,000rpm and are only used when in Neutral, if you have a neutral switch on trans or if neutral wire on computer is grounded

Above 4,000 reads like lack of fuel or too much fuel, or as said mechanical issues
MAF sensor could be wrong

What size injectors?

Wrong MAF can make it run rich, add that to wrong injectors size...................

I think the A3M was programmed for 19lbs injector, but 24lbs should be OK with correct MAF
And 30-40psi fuel pressure

 

[Acgallen]

Transmission has nothing to do with your problem... guaranteed. I don't believe anything Ford from that era had a rev limiter of any sort.

So it's a new engine - what parts did you use in your top end? Possible that you've got a weak valve spring(s) and you're simply floating valves at high RPM? Running out of fuel, timing off just a bit, plugs/plug wires arcing out, bad coil, something poorly grounded...?

How did you determine that it's running rich? Exhaust pops especially going downhill and engine braking are sort of normal, some mufflers make it much more obvious - my F150 never did that with stock exhaust but the second I put duals and glass packs on it, it would pop when engine braking. Doesn't mean it's running rich, you would need to look at data from an exhaust sniffer or live data on a scan tool to confirm that.

My top end consists of GT40P heads with stock springs and roller lifters. 19 lb stock yellow mustang injectors, new MAF, TPS is working, idle air works. Timing is at 11 degrees BTDC. Plugs and wires under 50 miles old. I will get back to you on fuel pressure but i wouldn't see how i would have messed that up. I dont believe i have a bad ground, I was chasing those for a while. I have true duals with no mufflers at the moment. I believe its running rich because of the smell and sound but i could be wrong. Im considering buying a new coil, but its not resembling a coil issue. Would expect more cutting out.

The A3M computer would have never been with the ZF5. Thats why im wondering if i need it flashed or chipped. Talked to a guy at Ford Carlisle and he mentioned a tune or a chip for it.

 

[Acgallen]

A3M is for manual trans V8
Yes, 1993 shouldn't have REV limiter but if it did then REV limiters are 3,000rpm and are only used when in Neutral, if you have a neutral switch on trans or if neutral wire on computer is grounded

Above 4,000 reads like lack of fuel or too much fuel, or as said mechanical issues
MAF sensor could be wrong

What size injectors?

Wrong MAF can make it run rich, add that to wrong injectors size...................

I think the A3M was programmed for 19lbs injector, but 24lbs should be OK with correct MAF
And 30-40psi fuel pressure

I can rev past 3k in neutral. I replaced stock MAF with new and it solved some intake popping problems. So i dont believe its a bad MAF. Running 19lb injectors. Im basically running a stock 93 mustang motor with GT40P heads.

 

[19Walt93]

I used to see Fox body Mustangs popping as the drivers hit the rev limiter on the drag strip so I'm pretty confident they had one. The man who cut my hair for the first 20 years of my life complained about his early 90's F150 cutting out on the highway and I figured out he was running up against the limiter that governed the top speed on his truck. What did your processor come out of? One from a T5 Mustang might work but if it's from an automatic I'd question it. Welcome to engine swaps and don't get discouraged, it'll be worth it once you get everything to play nice together.

 

[Shran]

Do you have catalytic converters on it? It'll smell like raw exhaust no matter what if they are gone. I wouldn't assume it's running rich just yet.

I'd be curious to see what your fuel pressure looks like at high RPM under load. Being able to rev past 3k in neutral but not under a load suggests to me that it may not have adequate fuel. Just something to look at, the Ranger fuel pump is plenty capable of supplying a stock V8 - maybe a weak pump or partially clogged filter? Kinked fuel line? I kinked one on my V8 swap and it took me years to find it but it didn't really cause any major issues.

My opinion on the computer/rev limiter deal is that if it came out of a manual trans donor vehicle, it doesn't matter what manual you put behind the engine... the computer doesn't look at the transmission for anything other than the speed sensor on the speedometer cable and maybe the neutral switch (not sure on that.) Otherwise as far as it's concerned, you could have a direct drive to the rear axle with no gears or a 4 speed or a 5 speed or a 10 speed from a semi... It would not know that you exchanged one manual for a different manual.

It might be worth getting a scan tool that can view live data from your computer if you rule out the other stuff we mentioned. Using an OBD-1 computer narrows your choices down a bit but the Bosch 1300/Actron 9690 have some rudimentary ability to do that. Might be a few others out there too. I have an old OTC System 2000 scanner that will show live data but only in the moment, no graphing.

 

[RonD]

Use a Vacuum gauge on intake
REV engine to say 2,500 and hold it there
Vacuum will of course drop as throttle plate is opened but then come back up when RPMs are steady
Watch the vacuum, if its slowly dropping you have exhaust restriction
If vacuum is slowly climbing you have intake restriction


Which spark system are you using?
Electronic advance or vacuum advance?

11deg BTDC is with spark advance disabled?
Have to disable spark advance to set Base spark timing

 

[Acgallen]

I used to see Fox body Mustangs popping as the drivers hit the rev limiter on the drag strip so I'm pretty confident they had one. The man who cut my hair for the first 20 years of my life complained about his early 90's F150 cutting out on the highway and I figured out he was running up against the limiter that governed the top speed on his truck. What did your processor come out of? One from a T5 Mustang might work but if it's from an automatic I'd question it. Welcome to engine swaps and don't get discouraged, it'll be worth it once you get everything to play nice together.

Processor came out of 1993 Mustang 5.0 manual tranny. Its a very weird cut out. Haha ive been discouraged for 2 years doing this swap, but im still here. Itll come, but maybe after a while

 

[Acgallen]

Do you have catalytic converters on it? It'll smell like raw exhaust no matter what if they are gone. I wouldn't assume it's running rich just yet.

I'd be curious to see what your fuel pressure looks like at high RPM under load. Being able to rev past 3k in neutral but not under a load suggests to me that it may not have adequate fuel. Just something to look at, the Ranger fuel pump is plenty capable of supplying a stock V8 - maybe a weak pump or partially clogged filter? Kinked fuel line? I kinked one on my V8 swap and it took me years to find it but it didn't really cause any major issues.

My opinion on the computer/rev limiter deal is that if it came out of a manual trans donor vehicle, it doesn't matter what manual you put behind the engine... the computer doesn't look at the transmission for anything other than the speed sensor on the speedometer cable and maybe the neutral switch (not sure on that.) Otherwise as far as it's concerned, you could have a direct drive to the rear axle with no gears or a 4 speed or a 5 speed or a 10 speed from a semi... It would not know that you exchanged one manual for a different manual.

It might be worth getting a scan tool that can view live data from your computer if you rule out the other stuff we mentioned. Using an OBD-1 computer narrows your choices down a bit but the Bosch 1300/Actron 9690 have some rudimentary ability to do that. Might be a few others out there too. I have an old OTC System 2000 scanner that will show live data but only in the moment, no graphing.

No cats on it. Ill get a fuel pressure gauges and get back to you. No kinked lines, but i cant rule out weak pump or clogged filter. Truck was working fine before the swap so im not so sure its a fuel problem. When driving around it wont cut out at all(Under 4k RPM) when up to temperature, have cruised in 5th at 70 mph. But when warming up the truck, the tach will randomly drop to 0 and the truck will either die or stutter back to life. Ill also grab a scanner and see if there are any codes, no CEL on the dash.

 

[Acgallen]

Use a Vacuum gauge on intake
REV engine to say 2,500 and hold it there
Vacuum will of course drop as throttle plate is opened but then come back up when RPMs are steady
Watch the vacuum, if its slowly dropping you have exhaust restriction
If vacuum is slowly climbing you have intake restriction


Which spark system are you using?
Electronic advance or vacuum advance?

11deg BTDC is with spark advance disabled?
Have to disable spark advance to set Base spark timing

I have almost open headers and a cold air intake with a stock throttle body. Ill test vacuum, but i just redid all my lines and got the proper routing. I believe its electronic advance. If your referring to the spout connector, it was taken out when i set timing.

 

[Snoranger]

The A3M has a 6250 limiter.

 

[Shran]

But when warming up the truck, the tach will randomly drop to 0 and the truck will either die or stutter back to life.

Weird, and ONLY when warming the truck up...? Are you using an aftermarket tach or the factory one? Of everything you've mentioned thus far, this is where I would start troubleshooting. Might be something simple like a corroded or loose wire on the coil. I would be tempted to try another coil too, probably unlikely but wouldn't hurt to rule it out.

 

[Acgallen]

Weird, and ONLY when warming the truck up...? Are you using an aftermarket tach or the factory one? Of everything you've mentioned thus far, this is where I would start troubleshooting. Might be something simple like a corroded or loose wire on the coil. I would be tempted to try another coil too, probably unlikely but wouldn't hurt to rule it out.

Yeah only when warming up. It will idle around 1000 and then just randomly B-line for 0 on the tach. It is a stock ranger tach. I will buy a coil and try a new one, hope its as simple as that. Oh and brand new dizzy.

 

[Shran]

Hate to suggest the parts cannon approach, might be more cost effective to pick a bunch of spare parts from the junkyard and swap them out one by one. I just feel like if your tach signal just totally goes dead and the truck dies and you've also got these other seemingly related issues, there is at least something going on in the coil wiring or the coil itself.... or the distributor... or the ignition module.

I'm not sure how 92 factory tachs are set up but on first gen trucks they are only accurate for V6 engines unless you add a tach signal converter box for 4 or 8 cylinders... I never did that with mine and it's nowhere near accurate. 3-4000 actual RPM will top out the gauge.