'03 5.4 Mach 1 Problem

5.4beast

New Member
Apr 9, 2014
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Ok, so I put a 5.4 DOHC into a '03 mach 1. Engine is rebuilt with a cobra jet intake. (with MMR plates). Car run strong with tons of torque. The only problem is that when its at idle, if I take off fast or even just pump the gas, the engine stalls. This car has been professionally tuned by premier. (very reputable dyno shop here in utah). They said it might not be getting enough air at idle, which sound opposite to me. But I'm out of ideas. I'm so close guys, please help!
 
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squeak93

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Jun 2, 2005
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It's likely in the tune unless the IAC isn't working correctly, which their data logs would have shown. Might want to get a second opinion there from another shop.
 

wmburns

SN Certified Technician
Aug 14, 2009
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Houston Texas
+1 on above.

But IF this were my car one of the first things I would confirm is the fuel pressure. Specifically confirm that the fuel pressure is being indexed to the intake manifold vacuum.

Is the fuel rail pressure sensor (FRPS) intake vacuum reference line connected and leak free? Is there any evidence of raw gas in the line?

Next would look for a vacuum leak between the MAF and the throttle body. Then followed by after the throttle body.

Now things start to get harder and an ODB2 scanner that is capable of data logging and graphing starts to show it's value. What I would graph is RPM, fuel pressure, MAF, LTFT, STFT, and IAC duty cycle at idle and during some throttle "blips". Plus some steady state running. Just want to know how the various parameters are doing as motor load changes.

Here's some information on an affordable windows based unit.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/
 

5.4beast

New Member
Apr 9, 2014
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Thanks, both of you! I'm taking it back to the tuner next Monday. Hopefully he'll get it. but if not, I have a route to take. ;)
 

5.4beast

New Member
Apr 9, 2014
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ok guys, Finally an update. I took it to the tuner, they have had it for months!! Basically they cant fix it. They checked for leaks, replaced the IAC, spent over 20 hours tuning. Still same problem. This is a VERY reputable tuner for mustangs in my area. Any other ideas?
 
Apr 17, 2018
88
5
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Michigan
What ECU are you running the engine with? Do you have an automatic or manual transmission?

The tuner shop's, "not enough air," could be right on. I'm going to guess that you missed the era of manual chokes or choked carburetors? For cold starts the choke would have the engine run rich with stunted or impeded air flow. Initiate the coke on a warm engine and it stalls. If your tuner is seeing something suggesting to them, "warm engine + too much fuel + not enough air = stall" then they were right. It may not lead them to the solution but it's a problem and a place to start for them.

Not knowing what is controlling your engine what first comes to mind is if you are trying to run a 5.4 with 4.6 Mach 1 controls there are some serious conflicts with the cams and injector pulse width.

What year did the Mach 1 offer an automatic? If you have an automatic, there are a number of torque convertor problems that can make the car stall: pump, clutch, locking up (lock up), etc. If the tuners couldn't solve the problem from looking at the engine and if you have an automatic, this might be the place to look.

With the information, or lack of it with what you've written there's no real way to narrow in on your problem to help. Hell, you don't even offer any information about the 5.4. You say you have lots of torque and that could be because it's a long runner truck or 4WD vehicle engine. The Mach 1's cam strategy isn't a good one for a truck engine. A truck or car engine is critical information you should be offering. Squeak93 and wmburns should be applauded for giving it a shot at trying to help you with some worthwhile info.
 

5.4beast

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Apr 9, 2014
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Ok, Thank you for the response! I have a manual trans in the car, which is what came in the car. The ECU I'm using is the mach 1 Ecu. The cams are the mach 1 cams. (although I've read the cams on the navi are the same, but to be sure, I used the mach 1 cams.)

To be clear, I meant that this car has tons of torque, but also revs well. It throws you into the seat much harder than it did with the 4.6. the motor sounds great, and runs great. Unless its cold, then it likes to stall on takeoff. (its actually hard to keep it from stalling. even if your taking off slow).

As far as the choke thoughts: not totally disagreeing to be clear. but the choke on the old carbs were meant to give you a richer mixture when the engine is cold. so more fuel, less air. What they suggested would increase air, but the mass air meter would compensate and just match the air/fuel ratio. thereby accomplishing nothing.

My hypothesis is that for some reason, the engine is running lean (or at least normal) when the engine is cold. when it needs to be slightly rich for a cold engine. But other that programming, which they have tried. I cant think of how to accomplish this..

I'm I on the right track? Or completely out of my mind?
 

wmburns

SN Certified Technician
Aug 14, 2009
5,878
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Houston Texas
My hypothesis is that for some reason, the engine is running lean (or at least normal) when the engine is cold. when it needs to be slightly rich for a cold engine. But other that programming, which they have tried. I cant think of how to accomplish this..
Normally the PCM would use the engine coolant temperature (ECT) and input air temperature sensor (IAT) to perform the function of a "virtual" choke.

It might be worth while to double check that the PCM is actually getting a valid ECT and IAT. Assuming that then if your theory is good then it's all back to TUNE.

FWIIW if your theory is true then the problem would only occur when the motor is cold.

A final thought is maybe the throttle body is too large for the idle air requirements of the motor. This creates a "lazy" air flow through the MAF thus not giving the PCM an accurate picture of the air entering the motor. To test the theory look at STFT during throttle "blips" to see if big changes are noted.
 

5.4beast

New Member
Apr 9, 2014
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wmburns: It is only when its cold. After about 5 minutes of idle, the car runs perfectly. You're throttle body idea is very intriguing to me though! I wont have it back to the tuner for a while, but do you think that blocking part of the throttle body off would be a good way to test this theory?
 
Apr 17, 2018
88
5
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Michigan
Your ECU has what's called a "special enrichment table," that is for cold starts and for cold starts you can forget about everything you know about your MAF controlled A\F mixture. It doesn't apply and most of the system downstream isn't working during a cold start. Hence the special table. This special table you're using is for the 4.6 and not the 5.4. Again to clarify, There is nothing in your engine making adjustments to the A\F mixture during a cold start. That is all hard wired in to the special enrichment table. All of this suggest that you're getting enough fuel to run because it does run. The efficiency it's running with is another question. It's not stalling because of fuel but because IMO it's starving for air because of a larger cylinder bore with air for a smaller cylinder bore. It's not producing the pressure needed to run at idle. A choke from another mother. Then there is the cam problem. I take Ford at their word that the Mach 1 had its own unique cam grind. Being "unique" suggests it's not being used on another engine. This is just speculation but the cam could very well be letting air out of the cylinder because of the pressure wave the 5.4 is creating with these cams.

As far as I know you can only change the table by pulling the chip from the PCM and reprogramming it. To do this you need to be proficient at hexadecimal locations within the Epromm. Another way would be to use an interceptor and program a new table in it to bypass the PCM table. Expensive! Your best bet is to try and track down the stock PCM for the 5.4.

IMO your tuner is right and this is not something a typical tuner can do or would attempt to do. Just my 2 cents.
 

5.4beast

New Member
Apr 9, 2014
26
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Your ECU has what's called a "special enrichment table," that is for cold starts and for cold starts you can forget about everything you know about your MAF controlled A\F mixture. It doesn't apply and most of the system downstream isn't working during a cold start. Hence the special table. This special table you're using is for the 4.6 and not the 5.4. Again to clarify, There is nothing in your engine making adjustments to the A\F mixture during a cold start. That is all hard wired in to the special enrichment table. All of this suggest that you're getting enough fuel to run because it does run. The efficiency it's running with is another question. It's not stalling because of fuel but because IMO it's starving for air because of a larger cylinder bore with air for a smaller cylinder bore. It's not producing the pressure needed to run at idle. A choke from another mother. Then there is the cam problem. I take Ford at their word that the Mach 1 had its own unique cam grind. Being "unique" suggests it's not being used on another engine. This is just speculation but the cam could very well be letting air out of the cylinder because of the pressure wave the 5.4 is creating with these cams.

As far as I know you can only change the table by pulling the chip from the PCM and reprogramming it. To do this you need to be proficient at hexadecimal locations within the Epromm. Another way would be to use an interceptor and program a new table in it to bypass the PCM table. Expensive! Your best bet is to try and track down the stock PCM for the 5.4.

IMO your tuner is right and this is not something a typical tuner can do or would attempt to do. Just my 2 cents.
Makes perfect sense! thank you!
 
Apr 17, 2018
88
5
8
Michigan
For the last week I've been in and out of the hospital, no big deal, and I've had a lot of spare time on my hands because I'm limited on what I'm "allowed" to do. Because I've had the time I've been through the manuals but most of the information doesn't fit your PCM to engine match, what engine you have is an unknown, not all 5.4's are created equal but some specs are consistent and getting hands on is out of the question. The one reliably consistent variable that fits everything you have described is the cold start strategy but a lot of the test point specs for the 4.6 and 5.4 are different for the strategy. The information I've given you fits IMO but I'm not saying that without a doubt this is what's going on. Since your 4.6 appears capable of adapting to the 5.4 when the engine is warm but not when it's cold it's not, it is an obvious culprit right or wrong, because it's not adaptable except for temperature. As far as I know the modular motors didn't use a secondary air injection system which is somewhat adaptable and your PCM is post the direct J-XXXX plug on the module for direct access to it.

What are the casting numbers on your engine? At least you can find out the year of the engine and maybe more. IMO your best bet is to track down the right PCM for you engine so the data needed can be pulled from it for the 4.6 PCM. Best of luck.
 

5.4beast

New Member
Apr 9, 2014
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The engine is a 2001 navigator engine. I have the engine info somewhere, I'll try and track it down. I think the hard part may be getting a PCM for this engine that will work with my standard tranny..