Ford Mustang Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter #1
I'm a newbie poster here but I've been searching this and other forums for a couple of years trying to resolve this particular problem. The car is a '01 4.6 (2V) GT. A few years ago I installed a brand new '03 4.6 (2V) GT crate engine. The engine is completely stock and bolted right in with all connectors matching up perfectly. The new engine has about 30K miles now and runs great with one exception; starting the car when the engine is warm takes multiple attempts. The starter cranks normally but the engine doesn't catch. The only remedy is to push on the accelerator pedal (not all the way down) and then feather it for about 15 seconds after it starts to keep the engine running. After that it will usually stay running. When the engine is cold (like when the car sits overnight), it starts right up without this issue.

Here's some history on steps I've taken during the two years: Replaced IAC valve, replaced TPS, cleaned MAF (the right way), replaced alternator (local Ford dealership's suggestion...the only time I've ever taking this car to someone else for help), replaced battery, replaced starter, replaced fuel filter, replaced CCRM (fix for a/c relay failure). Eventually after none of these things fixed the problem, I was thinking the issue was probably with the fuel pump, which was original with the car. That pump finally failed completely last week at 170K+ miles, but when I replaced it, the warm engine hard start problem was still there.

I put a fuel pressure gauge on the rail and believe that I have ruled out any fuel pressure issues as the root cause. I have OBD II scanner software and I used this to verify there are no trouble codes stored in memory. For that matter, this problem has never triggered the check engine light on the dash.

At this point I'm not sure which direction to go with this, but here are my thoughts about possible problems based on the searches I've done in the forums: Bad camshaft sensor, bad crankshaft sensor, bad coolant temp sensor, leaking fuel injector, bad EGR, vacuum leak (take it somewhere for a smoke test). Some of these involve expensive parts/tests so I would appreciate any thoughts on what to try next.
 

·
Super Moderator
Joined
·
40,051 Posts
Welcome to the site!!
Having the same problem.You can look at my threads in the 4.6 Tech and see what i have done and advice given.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #3
Thanks Heavy Metal. I just read through your "Excessive Crank When Warm" thread and our problems look very similar. One difference I noticed is that mine isn't throwing any codes. Anyway, there is some good info in that thread. There was a comment in there about the PCV valve. I forgot to mention that the replacement engine I installed has a heated PCV valve but the original engine in the car had a non-heated valve. I've actually replaced that valve with the same type but it didn't have any impact on the problem I'm having. I'm wondering if there could be some issue with the original PCM on the car ('01) not having any way to control that heated PCV valve on the new engine ('03)? Also, could there be any other issue with an '01 PCM managing an '03 engine?
 

·
Registered
Joined
·
6,859 Posts
Also, could there be any other issue with an '01 PCM managing an '03 engine?
^^ No issues at all as long as the fuel injectors used match what the PCM is expecting.

It would be nice to know what the PCM "thinks" the fuel pressure is before, during and after a warm crank.

It would also be nice to know what the PCM "thinks" the input air temperature (IAT) and engine coolant temperature (ECT) is.

But the fact that holding the throttle part open helps the issues suggests that the motor is not getting enough air to start. This could be:
  • incorrect IAC valve used for the application. IE PCM is expecting a black vent IAC and the non vented version installed.
  • Throtle body idle stop screw set too low.
  • incorrect throttle body used for the application. Some TB's have small holes that allow some bypass air to get through
  • vacuum leak between MAF and buterfly.
  • dirty or incorrectly indexed MAF. Such that MAF air flow is under reported to the PCM

For the IAC issue, what is the IAC duty percentage and RPM's when the motor is warm at idle? What happens if the IAC electrical connector is disconnected when the motor is warm at idle?
 

·
Registered
Joined
·
14 Posts
Discussion Starter #5
^^ No issues at all as long as the fuel injectors used match what the PCM is expecting.

It would be nice to know what the PCM "thinks" the fuel pressure is before, during and after a warm crank.

It would also be nice to know what the PCM "thinks" the input air temperature (IAT) and engine coolant temperature (ECT) is.

But the fact that holding the throttle part open helps the issues suggests that the motor is not getting enough air to start. This could be:
  • incorrect IAC valve used for the application. IE PCM is expecting a black vent IAC and the non vented version installed.
  • Throtle body idle stop screw set too low.
  • incorrect throttle body used for the application. Some TB's have small holes that allow some bypass air to get through
  • vacuum leak between MAF and buterfly.
  • dirty or incorrectly indexed MAF. Such that MAF air flow is under reported to the PCM

For the IAC issue, what is the IAC duty percentage and RPM's when the motor is warm at idle? What happens if the IAC electrical connector is disconnected when the motor is warm at idle?
Thank you for the inputs wmburns.

  • The engine is a factory surplus crate engine with no mods so the injectors and TB (and all other components) should match to the PCM's expectations.
  • I will check and report back with scan results for the fuel pressure, IAT, ECT, and IAC duty readings as you suggested.
  • I am confident the new IAC is correct. It's an exact Motorcraft replacement part without the black vent. It's my understanding the black vent type would have been used on earlier versions of this engine, but correct me if I'm wrong.
  • The throttle body set screw does not appear to be contacting the throttle mechanism at all. I assumed this wasn't a problem since the idle strategy was being handled by the PCM, but again please correct me if I'm wrong. Also, I didn't suspect this as being an issue since cold starts and cold idle were not a problem.
  • I've cleaned the MAF a couple of times but I cleaned it conservatively by only spraying with CRC MAF Sensor cleaner; I didn't apply any physical contact (like with a Q-tip) to the delicate wires. Should I take a more aggressive approach with that? The MAF is original with the car (170K+ miles).
  • When the IAC is disconnected the car stalls out immediately. I believe the warm idle is about 590 rpm's but I will confirm that as well.
 

·
Registered
Joined
·
6,859 Posts
A couple of points. The Mustang has not used the same size fuel injectors across to model years. Along the way the fuel injectors were upgraded from #19 to #21. So to say that the fuel injectors have to match because the motor was a factory surplus 2003 may not be entirely correct.

I do know that my 2003 had #21. Where as my 2000 has #19's.

I can also say positively that my 2000 GT has a black vented IAC. Where as my 2003 GT did not.

I honestly can't remember the exact model year that the standard fuel injector went from #19 to 21#.

What are the long term fuel trim (LTFT) values at idle and 1500 RPM's? One symptom of fuel injectors that are too large for the tune is large negative LTFT values. Of course this could also be a symptom of high fuel pressure.

If the throttle linkage does not rest on the idle stop screw, then the idle stop screw is NOT set correctly. For the idle to work correctly the throttle must return to the exact same position EVERY time. In a correctly working Mustang the IAC duty percentage is mainly between 40 and 60 percent. If it's almost always outside of this range, this means that the default closed throttle air flow is not correct and that the IAC is being asked to adjust too much.

I have helped someone in the past with an idle problem. The solution turned out to be that the idle set screw was backed off too far. This caused the butterfly to not be in the exact same position each time. At the very least, the throttle has to rest on the idle stop screw when the throttle is closed.

To add. Check the battery, battery cables, and alternator. Test the battery to be sure it holds a charge. Check the alternator for excessive AC ripple (bad diode).

Note, there are subtle difference between the model years. Many times the differences don't matter. Sometimes they do. Take for example the throttle body butterfly. Some model years have small "bleed" holes where others do not. The size of the bleed holes work together with the design of the IAC valve. Please don't ask me the exact model year where the change was made as I don't have that detailed of information.

I suspect that the TB butterfly bleed holes are related to the style of IAC used (black vent vs no black vent). I honestly don't know which the 2001 came with. My direct knowledge is with a 2000 GT and a 2003 GT.

Don't be more aggressive in cleaning the MAF.

Does this car have a cold air kit? What about the MAF holder. Has it been "indexed" in the same location as the factory unit? Incorrect MAF indexing can cause the MAF to read incorrectly. Again monitoring LTFT is a way to tell if the PCM is having to make adjustments.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #7
A couple of points. The Mustang has not used the same size fuel injectors across to model years. Along the way the fuel injectors were upgraded from #19 to #21. So to say that the fuel injectors have to match because the motor was a factory surplus 2003 may not be entirely correct.

I do know that my 2003 had #21. Where as my 2000 has #19's.

I can also say positively that my 2000 GT has a black vented IAC. Where as my 2003 GT did not.

I honestly can't remember the exact model year that the standard fuel injector went from #19 to 21#.

What are the long term fuel trim (LTFT) values at idle and 1500 RPM's? One symptom of fuel injectors that are too large for the tune is large negative LTFT values. Of course this could also be a symptom of high fuel pressure.

If the throttle linkage does not rest on the idle stop screw, then the idle stop screw is NOT set correctly. For the idle to work correctly the throttle must return to the exact same position EVERY time. In a correctly working Mustang the IAC duty percentage is mainly between 40 and 60 percent. If it's almost always outside of this range, this means that the default closed throttle air flow is not correct and that the IAC is being asked to adjust too much.

I have helped someone in the past with an idle problem. The solution turned out to be that the idle set screw was backed off too far. This caused the butterfly to not be in the exact same position each time. At the very least, the throttle has to rest on the idle stop screw when the throttle is closed.

To add. Check the battery, battery cables, and alternator. Test the battery to be sure it holds a charge. Check the alternator for excessive AC ripple (bad diode).

Note, there are subtle difference between the model years. Many times the differences don't matter. Sometimes they do. Take for example the throttle body butterfly. Some model years have small "bleed" holes where others do not. The size of the bleed holes work together with the design of the IAC valve. Please don't ask me the exact model year where the change was made as I don't have that detailed of information.

I suspect that the TB butterfly bleed holes are related to the style of IAC used (black vent vs no black vent). I honestly don't know which the 2001 came with. My direct knowledge is with a 2000 GT and a 2003 GT.

Don't be more aggressive in cleaning the MAF.

Does this car have a cold air kit? What about the MAF holder. Has it been "indexed" in the same location as the factory unit? Incorrect MAF indexing can cause the MAF to read incorrectly. Again monitoring LTFT is a way to tell if the PCM is having to make adjustments.
Wmburns, I need to correct one thing that I told you earlier about the throttle body set screw. It is actually making good contact with the throttle stop mechanism at idle. When I mentioned that it wasn't making contact in my previous post, I was stating that from memory since I was at work but I found out otherwise when I got home tonight and looked again. Sorry for that.

I took your advice about possible differences with the fuel injectors and did a parts lookup for both engines ('01 GT and 03 GT). Fortunately, they both use the same injector.

Regarding the IAC, I looked at pictures of the old engine and that one had the black vent style whereas the new '03 engine uses the non-vented one. So my
question is should I have replaced the IAC on the new engine with the old style vented one since the pcm is programmed to control that type? Or, to your point about the TB butterfly design, maybe it's more important that the IAC is properly matched with the TB as it is now?

Here are some of the scanner readings you asked about earlier...
Fuel Pressure before warm crank: 17
Fuel Pressure as engine is stalling (395 rpm's): 60
Fuel Pressure after engine starts and stabilizes: very consistent at 40 (after 30 seconds, 1 minute, 2 minutes)
IAT: 99 - 104 (from pre-start to 2 minutes running)
ECT: 174 -180 (from pre-start to 2 minutes running)
LTFT Bank 1/Bank 2 at 787 rpm (idle): 2.34 pct/0 pct
LTFT Bank 1/Bank 2 at 1500 rpm: 6.25 pct/9.38 pct

My scanner doesn't seem to have a PID called anything like IAC Cycle Pct. It does have Calculated Load Value Pct which is about 46 at idle.

The car and engine are completely stock so there is no cold air kit and the MAF is in it's original air box with the flow arrow oriented correctly.
 

·
Registered
Joined
·
6,859 Posts
As stated before, the IAC, throttle body, and PCM tune all work together to implement the idle strategy. Change any one and the results are unpredictable.

Note, I went to the oreillyauto web site to look up the IAC. Per this site, the 2001 GT uses a black vented IAC. Further looking at the compatibility tab shows the part is only good for the 2001 model year. So it wouldn't surprise me that if you have used an non vented model in a vented application then some problems could occur.

Motorcraft CX1917 - Idle Air Control Valve | O'Reilly Auto Parts

I know that in application using the non-vented IAC, the PCM has more responsibility to control air entering the motor via IAC. So if the PCM is tuned for the vented IAC, it's reasonable to assume that the PCM doesn't have any programming for the IAC at start up.

Note, the other thing of interest is the fuel pressure. In a correctly working car, the fuel pressure stays up between starts. Your fuel pressure is 17 PSI at initial crank. This indicates some level of fuel pressure leak down.

Try this trick. Turn the key on/pause/off several times WITHOUT cranking. Listen for the fuel pump to run each time. Now crank the motor. Does this improve starting? If so, then suspect fuel pressure leak down as a possible problem source.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #9 (Edited)
I have an '03 engine using an '03 (non-vented) IAC being controlled by an '01 PCM. Do I have the '01 PCM re-flashed to an '03 program or do I leave the PCM as is and replace the '03 non-vented IAC with an '01 vented IAC?

Yes, I've read about the key on procedure to pressurize the fuel pump and have tried it a few times when the engine was exhibiting the long crank/hard start issue, but it didn't change anything. Also, I've had a fuel gauge on the rail reading 40+ psi when it was exhibiting hard start, so I wasn't suspecting fuel pressure as the issue.
 

·
Registered
Joined
·
6,859 Posts
I have an '03 engine using an '03 (non-vented) IAC being controlled by an '01 PCM. Do I have the '01 PCM re-flashed to an '03 program or do I leave the PCM as is and replace the '03 non-vented IAC with an '01 vented IAC?
Well......I'm trying to figure out how best to answer this question.

Before I do, let me say that when cars are built/designed the PCM is designed to work within the car as a system. That means the PCM hardware, software, the car's wiring and sensors. The whole package.

For a car with a long model run time such as the Mustang the year to year differences can be small. Which promotes easy mix and matching between different model years. Sometimes this works and sometimes it doesn't. It just depends.

If asking for an educated guess it seems far safer (and easier) to swap the IAC instead of re-flashing the PCM with a different version of the software.

Using a new model year version of PCM software would presume there aren't other differences in the car's wiring systems that could come into play.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #11
Well......I'm trying to figure out how best to answer this question.

Before I do, let me say that when cars are built/designed the PCM is designed to work within the car as a system. That means the PCM hardware, software, the car's wiring and sensors. The whole package.

For a car with a long model run time such as the Mustang the year to year differences can be small. Which promotes easy mix and matching between different model years. Sometimes this works and sometimes it doesn't. It just depends.

If asking for an educated guess it seems far safer (and easier) to swap the IAC instead of re-flashing the PCM with a different version of the software.

Using a new model year version of PCM software would presume there aren't other differences in the car's wiring systems that could come into play.
Yes, that's the dilemma I was thinking about as well. Reflashing the pcm could impact other components/systems. I've ordered a new Motorcraft IAC from RockAuto. There was a vented IAC (CX1808) that showed applications for the 4.6 GT SOHC engine from late '01 to '03 even though my early '01 engine originally had the vented CX1917 and my new '03 engine came with (and I replaced with same a year ago) the non-vented CX1765. So basically, the one I ordered was not the exact part number that came on either the old or new engine, but it's vented like the old one and shows an application for the new engine. I'll provide an update when I get the part next week.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #13
Good news! My warm engine hard start problem is finally solved. The new IAC was the fix. The key was replacing the non-vented IAC with a vented version similar to the one that was on the original engine. Thanks to wmburns for getting me thinking about the vented vs. non-vented versions and how the PCM might be interfacing with them differently.
 
1 - 14 of 14 Posts
Top