2006 4.0L stall on hot start

[RGLL]

I have owned a 2006 Mustang V6 for 15 years and have been having a problem with hot starts for the last couple of years. The symptoms are, that after the car has been up to operating temperature and it sets for a few minutes and heat soaks, (I use 15 minutes for testing) it will start immediately and after about 1 to 2 seconds it will start to die with RPM down to maybe 200 and within 1 to 2 seconds it will most of the time pick right back up to normal idle. Sometimes if it is hot enough outside it will quit but during my 15-minute hot soak tests it will mostly regain normal idle, if it does quit it will start immediately on the second attempt and idle fine. There are no DTC codes. I have changed the following parts with Ford OEM and no change or improvements were noticed, FRPT sensor, fuel filter, spark plugs, and cleaned Throttle Body, Cleaned MAF And I have new spark plug wires, coil pack, EGR /ESM/MAP, MAF sensor, to install. But found recently when I was able to plumb a fuel gauge into the system and found an interesting symptom. The fuel pressure was normal when cold and would go up as the engine climbed to operating temperature and the mechanical gauge read about 10 less than the PID on my scanner as the manual says it should but due to the cheap Chinese gauge, when the engine was shut off the pressure did not drop, but after the 15 minute heat soak and I started the engine I noticed the fuel pressure dropped to less that 15 psi and corresponded to the engine beginning to die, as usual, just like above, but then the fuel pressure would come up and the engine would come back up to a normal idle. Now I had been thinking that the engine had been flooding, but now I find that its being starved for fuel causing the engine to almost die but coming back up to normal along with the fuel pressure. Now this Mustang at all times runs fine and starts normally when cold or after an hour when it has cooled down and it has just 100 miles on a complete overhaul of the engine, but it had the same hot start issue before the overhaul and after. The fuel tank was changed two or three years ago due to my daughter running over a toolbox on the interstate and is from a 2005 and I put a new fuel module and sending units in at that time so I'm thinking that the PPRV valve is defective as the module came from AutoZone, and it looks like Ford no longer produces a module. I have a fuel rail adaptor and fuel gauge on order and will be able to connect it to the fuel rail where the FRPT sensor goes and I hope to confirm the low fuel pressure after engine shut down, and I am also going to change the FPDM. Does anyone have an idea of the best fuel pump module to get? or any other tips that might help me to positively diagnose this as a bad fuel pump? JeremyH has a lot of good posts.

 

[Juice]

No codes = no direction to go.
I would deal with it as it sounds like the car drives fine, aside from hot restarts.
If the fuel pressure is out of whack, it should be tripping the light. Can you scan it for pending codes? Those dont throw the light till the code matures into a fault.

 

[Pentalab]

Break ur post into smaller paragraphs ! On my 2010 GT, I had issues years ago. Turns out it was the 'sock filter' that goes on the bottom of the oem fuel pump...at the bottom of the gas tank. The sock filter was clogged with crap. Once cleaned out, it ran like a top. I had crap floating around at the bottom of the tank.

 

[RGLL]

Thanks for the replies! Just did a test by starting it cold and let it warm up for 2 minutes, my cheap scanner was showing 40 PSI PID value, I pulled fuse 41, engine died immediately, went to the scanner as quickly as i could maybe 5-10 seconds and pressure was down to 27psi. I then did my 15-minute heat soak, and the pressure went to 19psi I then let it sit for an additional 15 minutes, and it went down to 10 psi subtracting 7-10 psi from the PID values as the service manual states shows basically 0 psi if I had a mechanical gauge on it. So it looks to me the PPRV valve is faulty. I will check it again when the fuel rail adaptor and fuel gauge comes in. Any suggestion for a quality pump ?

 

[RGLL]

Also does anyone have source for just the PPRV valve ?

 

[Pentalab]

Also does anyone have source for just the PPRV valve ?

dumb question. what is a PPRV valve....and where is it installed ? Is it a one way fuel valve ?

On a similar note, with key ON, eng OFF...and allowing time for my aeroforce gauges to boot up, (they plug into OBD port). I see 50 psi fuel pressure. Turn eng on, and it's 40 psi. Stays put at 40 psi, idle or wot.

 

[RGLL]

GlassTop09, has a very good explanation of the PPRV valve in his post from FEB 20th 2020 post #16 where he quotes JeremyH. I'm sure I could find several used ones from EBay but who knows if they would be any better. I have not been able find any specs for it. Also most of us think of this valve as the "Check valve" on the fuel pump module.

 

[Pentalab]

GlassTop09, has a very good explanation of the PPRV valve in his post from FEB 20th 2020 post #16 where he quotes JeremyH. I'm sure I could find several used ones from EBay but who knows if they would be any better. I have not been able find any specs for it. Also most of us think of this valve as the "Check valve" on the fuel pump module.

so the PPRV valve is a part of the fuel pump....at the bottom of the gas tank?

 

[RGLL]

Yes ' it's the white oblong valve and is right below the hat outlet.

 

[RGLL]

Fixed it! Put a new 150LPH USMW pump in and now it starts fine when hot. I'm now working on STFT and LTFT, at operating temperature and idle, STFT is around -.2 to + .5 on both banks and LTFT is - 18 on both banks. Going by forums it is stated that a good system should be -10 to +10 on both. Also one of the HO2S seems stuck on 99.2% or at least I never see it change. Any ideas which way to go? I'm thinking replace all four O2 sensors.

 

[RGLL]

New information and new problems. The hot start has been solved by installing a new fuel pump module (fuel pump only). It was from USMW purchased from Rock Auto for $33. It flows about 35 more LPH than the factory pump. The pump module that was installed about three years ago when my daughter ran over a toolbox on the highway and put a hole in the transmission pan and the fuel tank, was a Carter brand and seemed to work as the service manual said except for one thing. From my multiple testing of the old Carter pump including with the original FPDM and the new FPDM that I installed (before) changing the fuel pump motor, I discovered that on a cold start the fuel pressure would immediately drop from 40psi down to 20psi and then immediately go back up to 40psi in the space of about 3 to 4 seconds. This caused absolutely no problem on a cold start or cooled off time of about 45 minutes after shutting down, but when the engine was still hot this drop in fuel pressure was what was causing the engine to drop RPM and sometimes quit altogether. It would always start immediately if it quit after this drop in fuel pressure because now the pressure was back up to 40psi. And it would run fine until you would shut it off, and it would either cool all the way down, or it would do the stumble on a hot start up again. It did this with the old original FPDM and also with the new factory FPDM. So now out of desperation and an OCD to fix it one way or the other, I purchased the pump from Rock Auto and installed it and had to spend more than $20 to get 1 foot of submersible 3/8-inch fuel line (only needed about 2 inches). I also designed and built a tool to compress the large Oring on the pump making it a simple task to remove and install the lock ring. Now the strange thing is that the new pump did the same fuel pressure drop when the engine was cold but would stay steady at 40psi during a hot start and no more hot start problems occurred after multiple start and heat soak tests over the next couple of days. I could never find any documentation that this is a normal occurrence for the fuel pump, so I have to assume the drop in fuel pressure when engine is cold is a PCM thing possibly to guard against flooding the engine when it is cold. But its fixed and I hope this helps anybody else having a similar problem.

 

[RGLL]

The new problem!
While trouble shooting and eventually fixing my fuel pump problem from my last post, I noticed that my coolant temperature gauge was now going to red line and setting at midpoint when cold, stepper motor of course. My scanner showed normal temperature. So, I sent the cluster to Circuit Board Medics for repair and for the week that it was gone I replaced my MAF, EGR/MAP, PCV, coil unit, sparkplug wires, and four new HO2S.
When I received the cluster, I installed it but when KOEO it was totally dead! I removed it again and unplugged and reconnected the connector and now on KOEO it was powered up and looked normal. I took it on a drive and the car quit three times just like you shut off the key. after the third time it would not restart and was a no crank, no start, all dashes on odometer and no communication with the PCM and OBD2 scanner did not work.
I had it towed home and let it sit until the next day when prior to pushing it into the garage I tried the key, everything looked normal on the cluster, anti-theft blinking normally, odometer showing miles, and it started right up.
I then was trouble shooting wiring, fuses, relays and I changed relays and the PCM diode and cleared the KAM by jumper wire between positive and negative. It started up fine and was reading live data and was pleased to see the new O2 sensors seemed to be working as the long-term fuel trims were now down to about -10 instead of -20 and they were getting better but before the engine was completely up to operating temp Bam! it quits dead again with the same symptoms on the cluster as before. Let it cool down starts up and does it again over and over.
I'm about ready to run it into the river! There are lots of posts on this forum about this same thing happening to others but very few resolutions as to what fixed it for them. Circuit Board Medics have not returned my email asking if it's possible that the cluster is causing it since it never happened before they repaired it, and it is surely not the PCM diode.
Is it most likely to be the SJB, or the PCM, or grounds, Or the cluster. I see today a post about the PCM costing $1000. Any help would be very appreciated

 

[DieHarder]

Sounds like you have a heat related intermittent. Below is how I would approach troubleshooting this. The first couple of steps are more about eliminating suspects ..... YMMV

Recommend inspecting Grounds first. Are they green/sulfated? If so, it's a good idea to replace the battery harness. You can try cleaning them. Follow, remove, clean/sand & reconnect (one connection at a time) both positive & negative cable connections for the battery, passenger strut tower, starter, alternator and block. (Disconnect the battery first of course).... Retest - check voltage w/engine running across the battery terminals - should be 14.5 - 14.75 vdc. Any changes?

New battery harness: OEM Motorcraft: WC-95954 - https://www.ebay.com/itm/2974001768...IzO7NywSZOKMDS3YSHoscmTg==|tkp:Bk9SR7bphPLrZQ

If not, remove and inspect the SJB and other connectors down there for the same thing (corrosion/green/sulfated). If they are try cleaning the contacts/pins with electrical contact cleaner and tooth brushes. Retest - any changes?

Last (or first depending on how you want to approach it), you can try to recreate the fault by flexing cables in the engine bay. If you can make it quit while it's idling you're in the right area.

 

[RGLL]

Yes I have inspected all the grounds even the dreaded one on the back of the engine and they all read battery voltage which was at 12.5. I had previously cleaned all the ground when i was overhauling the engine. I was just in the garage trying to find the Auxiliary Relay Box 1 shown on the wiring diagrams but no luck, some others have said it doesn't exist but it contains the key off relay and diode Have you ever seen it? Circuit Board Medics did email me and wanted vin number and some more details and seems like they are willing to help. They did say that the PATS system is in the PCM, but I knew that, and PATS will not shut down a running engine. I'm trying to determine how to tie in some test lights to the PCM power inputs to see if the power goes out when it quits, my scanner doesn't show anything happening it's just like i have turned off the key.

 

[DieHarder]

Yes I have inspected all the grounds even the dreaded one on the back of the engine and they all read battery voltage which was at 12.5. I had previously cleaned all the ground when i was overhauling the engine. I was just in the garage trying to find the Auxiliary Relay Box 1 shown on the wiring diagrams but no luck, some others have said it doesn't exist but it contains the key off relay and diode Have you ever seen it? Circuit Board Medics did email me and wanted vin number and some more details and seems like they are willing to help. They did say that the PATS system is in the PCM, but I knew that, and PATS will not shut down a running engine. I'm trying to determine how to tie in some test lights to the PCM power inputs to see if the power goes out when it quits, my scanner doesn't show anything happening it's just like i have turned off the key.

With the engine running while measuring across the battery terminals? If you're only getting 12.5 vdc at idle your grounds need work. Do you have a Volt/Ohm meter?

 

[RGLL]

I just remembered that the test drive that I was on when it stalled three times was the first time it was driven with the new coil from Rock Auto and also the MAF and MAP/EGR valve and I have read many posts about coils getting hot and going dead. Hmm! don't know if that would explain the dashes on the odometer, no fuel pump, no crank, and no communication though.

 

[RGLL]

DieHarder'
Sorry I neglected to say that the battery voltage was taken with engine off, and was 12.5 and with engine at idle it is 14.6

 

[RGLL]

My latest research says the instrument cluster is the gateway module for the CAN-BUSS network and there are two 120 OHM resistors that might be going bad, but I haven't tracked down where each of them are located, but I expect one is inside the PCM and one in the cluster.

 

[RGLL]

Well it is running right now has been for two hours, no amount of tapping ,pulling on harness's or terminals, PCM, ABS, SJB ,fazed it, the only thing that I did different was charge the battery to 100% which had not been done before the aforementioned stalling, and I was wrong on the voltage across the battery it is only 13.7 to 13.9 sometimes 14.0 so maybe I do have a bad ground or that big speaker /amplifier in the trunk, which is hooked directly to the BEC terminal is drawing too much power. I think it is a 500-watt amplifier with a big 10-inch speaker that my oldest daughter had installed way back in 2013 and now that I think of it, we have put in at least 5 new batteries and a new alternator in the last ten years, and I always suspected that amp. I will disconnect it in a while and see what the voltage is. Specs according to the service manual on the alternator is 13.2 -15.5

 

[RGLL]

I removed the amplifier in the trunk and voltage is up to 14.2 at the best. Did I read somewhere that the voltage on a 2006 is controlled by the PCM like most of the new cars have a smart alternator. My daughters new Subaru got me there as it was reading 12.5 across the battery but she had just had the car quit on her at a stop light, thankfully it started right up. But I learned that certain driving styles will cause the battery to discharge to the point that ignition shuts off. The trick is to drive with your lights all the time or at least for a few minutes a day as that bypasses the smart alternator circuit. Of course, this was after rushing to the stealership only to have they say THEY thought that was normal. Ha! Do you know what new alternators are set at the factory its a couple of years old from autozone.