Electrical Hard to Start, Rough Idle, Won't Rev Up/Barely Any Power to Drive

rdmcalli

Member
Jan 7, 2006
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I hope to get some expert help ([email protected]).

I did a TFS1 cam upgrade & fox body EFI swap (X3Z PCM) in my 1966 Mustang with a C4. The car is hard to start. It initiaruns while cranking, but almost immediately dies with the key in the run position until it begins to warm up. Then it idles okay...Not great, and it won't rev up. It stumbles with no acceleration when opening the throttle in neutral or drive. It pops in the intake as if it is going lean. WOT does nothing but bog down. If I let off the throttle it barely accelerates when the throttle is almost closed.

The harness is from a 1991 5-speed and the EGR, air injection & canister purge emissions wiring was removed from the harness. No VSS or clutch safety switch are present.

I did the cam & EFI together on an otherwise good running motor. The engine is a '99 Explorer 5.0L short block, ported 351W D0OE heads (Autolite 45 spark plugs), 1.7 rockers, 1993 Cobra 70mm MAF, 24lb injectors, 65mm Explorer TB with fox TPS & IAC, ported Explorer lower & GT-40 Lightning tubular upper intake manifold. External F150 fuel pump (1988-ish style).

This PCM has been stored on the shelf the past 17 years. Initially this new-to-me X3Z PCM had a burnt trace on pin 46. I soldered in a jumper. The capacitors appeared good (no leaks/corrosion) when I recently looked at them.

Fuel pressure is mid forties & jumps to about 50 psi when the regulator's vacuum line is unplugged. The fuel rail & regulator are from a mid-1990s F150, so the pressure is a bit higher than a Foxbody. The pump & filter are new. I tried pinching off the return to rule out the pump with no throttle improvement.

No abnormal KOEO codes, good fuel pressure, base timing 12°, no apparent vacuum leaks, new spark plugs, & I did a base idle reset after verifying TPS voltage was in spec. The IAC motor was cleaned and is working.

I swapped the TPS, ACT, and barometer sensor with used spares without improvement.

I unplugged the MAF without a change. I removed the K&N air filter and idle slightly increased (maybe 75 RPM), but is still rough. I cleaned the MAF. It still won't rev up.

I tried an A9L & 55mm MAF (without swapping back to 19lb injectors) and it ran much better. Not ideal, but it revved in neutral and idled well from a cold start. Is this X3Z computer not working? Are there any specific tests that I should do?
 
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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Have you started by dumping codes to see what the ECU doesn't like, if anything?

Your fuel pressure is a bit high. The fox ECU is calibrated to expect a fuel pressure of 39psi vacuum off, and should hover somewhere in the mid to low 30's during normal idle. The ECU will reduce duty cycle to the injectors, but I do not know if it will be able to compensate fully for the elevated pressure. Injectors can only cycle so fast. As duty cycle drops at idle, the ECU will have a harder time trying to control air/fuel mixture and if it can't, that might account for some of your issues.

I would dump codes first though and start there. Vacuum leaks can also cause similar issues.
 
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manicmechanic007

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The processor will not like the egr deleted from the harness
It will throw itself into limp mode and stick the timing at 10 degrees and leave it there
Along with other trouble
Try plugging a evp sensor into the wiring sockets you deleted (or rewire it back in) and recheck
 

rdmcalli

Member
Jan 7, 2006
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Ignition timing is correct, H.O. firing order & seems to advance as it should.

I need to get a different fuel pressure regulator for sure.

The only KOEO codes I get are 31, 67, 81, 82, 84, and 85. These are all expected due to the emissions components deleted & neutral drive switch.

Can using resistors to simulate the EGR, canister purge & thermactor air circuit be helpful?
 

jrichker

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The odd duck is the 93 Cobra computer, labeled X3Z which is internally calibrated for 24 lb. injectors. Use the MAF & MAF sensor from the X3Z computer to avoid problems with the computer's internal calibration. Try and avoid the 93 Cobra computer if you can.

You should be able to use the correct sensor in a 70 MM housing with no problems.
Try the common parts store lookup to get the Mass Air MAF and sensor part numbers.

Try this link as an aid to finding the proper Mass Air MAF and sensor.
 

rdmcalli

Member
Jan 7, 2006
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The odd duck is the 93 Cobra computer, labeled X3Z which is internally calibrated for 24 lb. injectors. Use the MAF & MAF sensor from the X3Z computer to avoid problems with the computer's internal calibration. Try and avoid the 93 Cobra computer if you can.

You should be able to use the correct sensor in a 70 MM housing with no problems.
Try the common parts store lookup to get the Mass Air MAF and sensor part numbers.

Try this link as an aid to finding the proper Mass Air MAF and sensor.
Thank you for your reply.

Unfortunately, I have been using the correct Cobra MAF in its 70mm housing with the Cobra X3Z and 24lb injectors. (Any testing with an A9L swapped in from another car also included the correct 55mm MAF.)

Are there any specific tests that I should do to test this X3Z PCM?
 

jrichker

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There are two different 5.0 firing orders - which one do you have?

This doesn’t prove that the block is a HO block. Some trucks evidently use a HO firing order with a low lift cam (this will result in less than the desired HP output). However, it will definitely prove that a block can’t be HO because the firing order is wrong.

Remove the #1 & #3 spark plugs. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Slowly turn the engine until the TDC mark and the timing pointer line up. Mark TDC on the balancer with chalk or paint. Put your finger in #3 spark plug hole and crank the engine 90 degrees. You should feel pressure trying to blow past your finger. If you do not feel pressure, repeat the process again. If you feel pressure, it is a HO engine.

No pressure the second time, remove spark plug #5. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Put your finger in #5 spark plug hole and crank the engine 90 degrees. If you feel pressure now, the engine is not a HO model, no matter what it says on the engine.

Using a small carpenter or machinist square to mark the harmonic balancer off into 90 degree sections may be helpful here.

A 15/16 deep socket & breaker bar or ratchet may be used to turn the engine.

The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8
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manicmechanic007

5 Year Member
Sep 26, 2017
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There are two different 5.0 firing orders - which one do you have?

This doesn’t prove that the block is a HO block. Some trucks evidently use a HO firing order with a low lift cam (this will result in less than the desired HP output). However, it will definitely prove that a block can’t be HO because the firing order is wrong.

Remove the #1 & #3 spark plugs. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Slowly turn the engine until the TDC mark and the timing pointer line up. Mark TDC on the balancer with chalk or paint. Put your finger in #3 spark plug hole and crank the engine 90 degrees. You should feel pressure trying to blow past your finger. If you do not feel pressure, repeat the process again. If you feel pressure, it is a HO engine.

No pressure the second time, remove spark plug #5. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Put your finger in #5 spark plug hole and crank the engine 90 degrees. If you feel pressure now, the engine is not a HO model, no matter what it says on the engine.

Using a small carpenter or machinist square to mark the harmonic balancer off into 90 degree sections may be helpful here.

A 15/16 deep socket & breaker bar or ratchet may be used to turn the engine.

The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8
attachments\51122
The mis match might be the whole issue
 

General karthief

wonder how much it would cost to ship you a pair
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I would first see if the computer will communicate with a code reader, actually I would send it out to get checked, I don't know where you're at but I've used ECU Exchange, you can find them on eBay, I would also do a compression test, since you have 351w heads and other parts that are odd this will not be an easy fix.
What distributor are you using?
Give us a pic of the engine installed.
Is the ground in the injector harness attached to the intake?
Are you using the correct timing pointer?
 
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rdmcalli

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Jan 7, 2006
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I've been reading KOEO codes with a test light.

I'm using the Foxbody distributor.

Yes, the intake is grounded. The other grounds are good too.

I'm timing it on the Foxbody 10 o'clock pointer & verified TDC.

I'm going to send the PCM out if I can figure it out.

The 351W D0OE heads are comparable to GT-40 heads. Really, it is basically a '93 Cobra motor with a TFS1 cam, but I'll do a compression check tomorrow.
20211213_193457.jpg

20211213_193720.jpg
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
23,745
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I've been reading KOEO codes with a test light.

I'm using the Foxbody distributor.

Yes, the intake is grounded. The other grounds are good too.

I'm timing it on the Foxbody 10 o'clock pointer & verified TDC.

I'm going to send the PCM out if I can figure it out.

The 351W D0OE heads are comparable to GT-40 heads. Really, it is basically a '93 Cobra motor with a TFS1 cam, but I'll do a compression check tomorrow.
20211213_193457.jpg

20211213_193720.jpg
I'm going to make a suggestion in regards to that air filter, you should have a pipe to move the filter away from the maf, the reasoning is air moving through the filter will tumble (turbulence) around and cause inconsistent maf readings, there needs to be 6" +- between the filter and the maf so the air can straighten out for consistent readings, you can use a shorter filter if needed, I would also shield the filter so liquid does not splash on it. While this has little to do with your problem it's just a little thing that can keep problems from arising.
And investigate a clutch fan and shroud or an electric fan setup.
Nice work so far.
 
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90sickfox

Wasn't a pretty sight...and I've got big hands
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My 88 e150 had three fuel pumps and 2 tanks. There was a pump in each tank and a pump mounted to the frame after the selector switch. The ones in the tank were low pressure booster pumps and the one on the frame was a high pressure pump. Ford must've seen a reason for this. Maybe it is cavitation trying to pull the fuel through the line from the tank. The extra oxygen will cause a lean issue and the car would run like crap but pressure would look good. Just a thought.

Run a hose from the pump into a bucket and submerge it in fuel. When you cut the pump on you shouldn't see a whole lot of bubbles rising up from the submerged line.

Usually, the pump would be submerged in an EFI mustang so the theory would be different. Any air introduced after the pump would cause low pressure but in your case the pump could be compressing it. Also, all external pumps should be mounted below the fuel level line. Pumps do really good at pressurized fuel but not sucking it up. They usually depend on a siphoning effect for that. This is probably why the f150 and e150s had booster pumps submerged in the tank to feed the external pump.
 
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CAMTWO1070

Active Member
Dec 17, 2021
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I hope to get some expert help ([email protected]).

I did a TFS1 cam upgrade & fox body EFI swap (X3Z PCM) in my 1966 Mustang with a C4. The car is hard to start. It initiaruns while cranking, but almost immediately dies with the key in the run position until it begins to warm up. Then it idles okay...Not great, and it won't rev up. It stumbles with no acceleration when opening the throttle in neutral or drive. It pops in the intake as if it is going lean. WOT does nothing but bog down. If I let off the throttle it barely accelerates when the throttle is almost closed.

The harness is from a 1991 5-speed and the EGR, air injection & canister purge emissions wiring was removed from the harness. No VSS or clutch safety switch are present.

I did the cam & EFI together on an otherwise good running motor. The engine is a '99 Explorer 5.0L short block, ported 351W D0OE heads (Autolite 45 spark plugs), 1.7 rockers, 1993 Cobra 70mm MAF, 24lb injectors, 65mm Explorer TB with fox TPS & IAC, ported Explorer lower & GT-40 Lightning tubular upper intake manifold. External F150 fuel pump (1988-ish style).

This PCM has been stored on the shelf the past 17 years. Initially this new-to-me X3Z PCM had a burnt trace on pin 46. I soldered in a jumper. The capacitors appeared good (no leaks/corrosion) when I recently looked at them.

Fuel pressure is mid forties & jumps to about 50 psi when the regulator's vacuum line is unplugged. The fuel rail & regulator are from a mid-1990s F150, so the pressure is a bit higher than a Foxbody. The pump & filter are new. I tried pinching off the return to rule out the pump with no throttle improvement.

No abnormal KOEO codes, good fuel pressure, base timing 12°, no apparent vacuum leaks, new spark plugs, & I did a base idle reset after verifying TPS voltage was in spec. The IAC motor was cleaned and is working.

I swapped the TPS, ACT, and barometer sensor with used spares without improvement.

I unplugged the MAF without a change. I removed the K&N air filter and idle slightly increased (maybe 75 RPM), but is still rough. I cleaned the MAF. It still won't rev up.

I tried an A9L & 55mm MAF (without swapping back to 19lb injectors) and it ran much better. Not ideal, but it revved in neutral and idled well from a cold start. Is this X3Z computer not working? Are there any specific tests that I should do?
You need a chip and a custom tune to make it all jive together.....You cant just change stuff and expect the stock computers to respond to the changes unless you set the vehicle up exactly stock....Theres parameters that are burnt internally that the computer must adhere to....
 

CAMTWO1070

Active Member
Dec 17, 2021
147
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Heres a visual comparison of just a handful of the many many parameters that ened to be tweaked,especially the MAF transfer....

This is the difference between my 408 and modded 302 parameters......The ECU cant deliver anymore than whats on the menu...

Take notice to the injector high slope and low slopes...Thats the injector sizing the ecu goes by...
Screenshot 2022-05-07 150046.jpg
Screenshot 2022-05-07 145723.jpg