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Hard warm starts 1999 4.0 SOHC

99SportX

Explorer Addict
Joined
May 14, 2003
Messages
2,009
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City, State
Duluth, MN
Year, Model & Trim Level
1999 Ex & Mounty
Hello,

For the past year I have had a warm start issue with the SOHC. It starts perfect every morning. It also starts just fine after sitting all day at work. It only has issues starting when warm. It will crank for an extended period of time (5+ seconds) before starting with a bit of a stumble. Sometimes it will quit just after starting but then start the next time. I can get it to start faster and more reliably by holding the gas pedal down about half way. It has always started so I never really cared to fix it, but now it is starting to get old. This weekend I got a misfire cyl 6 (P0306) code just after one of the rough starts.

I purchased a fuel pressure gauge from harbor freight. I hooked it up and when I turn the key to on, the pressure rises and settles at 65 psi. When cranking I can see the gauge pulsing between around 50 and 65 psi. Once the truck starts it stays steady at 65 psi and I can hear the fuel pump humming away when I listen near the tank. I have not revved up the engine much, but it didn't seem like it changed a lot when I let the rpm's rise some. Once the engine is shut off, the pressure immediately drops to 60 psi. After that it starts to slowly drop. I would say it loses 10psi in the first 5 or so seconds, and is down to 30psi after about 30 seconds. When I came back after 30 mins it was down to 10 psi.

As far as I know, this rate of leakdown is not normal. I am assuming the pressure leaks down whether it is cold or hot. Why does it only have hard starts when the engine is warm? I cycled the key many times and let the pressure drop from 60 to 30 multiple times. I would assume that if there was an external leak, that I would have seen something dripping. That leaves internal leakage. I don't even want to think about a leaking injector. :( I found this post about an internal tank leak : http://www.explorerforum.com/forums/showthread.php?t=222895

Once the truck gets running, it runs just fine. The idle may be just a little bumpy, but nothing severe. When climbing a hill at lower rpms under load, the truck sounds a little funny, kind of has a raspy crackling tone to the exhaust. I think I may have a hole in the muffler somewhere though. Could this be a pinging noise due to running lean? Why no codes? Under load there is obviously more fuel demand so I may have to watch my fuel pressure when climbing a hill.

When I bought this truck about 3 years ago, the fuel tank was in the rear cargo area. The owner started to change the fuel pump and gave up on it due to ongoing transmission issues. I installed a used fuel pump I got from a fellow member along with a new strainer and a new inline filter. The tank was inspected and was quite clean inside. I did not replace the short sections of hose between the pump, pressure regulator and hard output line. Everything was fine and dandy for quite some time, but now it just doesn't want to run as well.


Any thoughts or suggestions are appreciated.:thumbsup:
 



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fuel pressure drop

I agree that your fuel pressure drops rapidly. My fuel pressure fluctuated +/- 2 psi from 65 psi at idle but was steady at 65 psi at 3000 rpm. After shutting the engine Off the pressure dropped to 62 psi in the first minute and remained there for more than 10 minutes. The photo below posted by ranger7ltr on one of my helpful threads shows the fuel pump assembly.
FPAssy.jpg

The hose could be split, the clamps could be loose, or the fuel pressure regulator could be defective. On my Volvo 850 turbo wagon a previous owner had replaced the fuel pump and used the wrong type of fuel hose. The fuel actually disolved the hose over a period of time.

Before pulling the pump assembly I suggest checking for external fuel leaks. I had a leak develop on my Sport in the short length of flexible hose between the fuel tank and the rigid fuel line.
split.jpg

Once again a previous owner had replaced the hose with low pressure fuel hose instead of high pressure.

If one or more injectors were leaking that much I suspect that a rich code would be set for the appropriate bank.

The rapid drop of fuel pressure may not be the source of your hard warm starts but it is something that should be investigated and corrected.
 






I will cycle the key a bunch more times and let the pressure go from 65 to 30 in hopes of seeing something dripping. I did see a drop of liquid under the truck today, but it was the drivers rear shock dripping oil since it is toast. hah

I didn't mention it in the first post, but I too replaced that same section of line where you had the leak. I used some hard plastic fuel line from napa with a new quick connect and a compression fitting to adapt to the hard stock line. All parts are designed for a high pressure fuel injection system. I saw how much fuel came out when I hooked up the pressure gauge. If the pressure is dropping as fast as it is, I should see something on the ground right? or at least obvious wetness somewhere along the supply line or fuel rail?

I also put my hand near the tailpipe and the exhaust flow at idle seemed really low. It wasn't too warm either. I was able to press my palm over the pipe and the engine didn't seem to care. I must have a pretty good exhaust leak somewhere because I was sealing it off so well it should have killed the engine.
 






Hello Eric, good to see you here.

Did the old pump hoses look great when you tightened the clamps? I doubt that you have a leak going into the engine, but I would use a good injector cleaner, and change the filter too.

How quickly does the pressure come up with one turn of the key, engine warm? If it doesn't get to 55+ immediately, I'd try on the next attempt, to turn the key on but don't go to start. Then turn the key off, and then on and start. I had my old 93 require three turns of the key to on for it to start when cold. When hot it didn't matter(slow leak down).
 






Hey Don. Its been a while. I haven't seen you over on 'the other side' for a long time. :)

I feel I have pretty good judgement when it comes to the condition of the hose. I may have used the rubber hoses from a lower mileage sender assembly I had lying around because I seem to remember the hoses from the one that came with the truck were hard. It may not have clamped well since it had previous crush marks from the original clamps.

When the pressure was down to 10psi, it came up to 65 at the first prime cycle.

I was just under the truck again after cycling the pump about 10 times. I noticed a slight dampness where my compression fitting meets the stock steel line. There is nowhere near enough fuel lost to result in such a rapid pressure decrease. When connecting the gauge, there was a good deal of fuel sprayed out in the time I connected the schrader. I would expect a similar loss of fuel going from 60psi to 0. I think I have no choice except to drop the tank and inspect. It isn't a big deal. I can't get to my compression fitting too well unless the tank is out of the way anyway.

Once I get the fuel pressure issue out of the way I can move on to further diagnosis. I thought finding an exhaust leak would be easy, but it doesn't seem to be. I think I will stuff a rag in the tailpipe and seafoam it. :D

It could be that my crank pos sensor is getting weak and provides a poor signal to the ECM at lower engine speeds.

I watched the engine coolant temp readout on my Xcal2 and the readings seem logical. I had about 183 when up to temp and the readout matched ambient at first startup outside in the morning.
 












I could do that. It might be a week until I can get my act together and record some data. I think I have to reinstall the software on my laptop. Are there certain parameters I should be recording?
 






Which fuel pressure test guage did you get from Harbor freight? Did it come with the adapter/hose to fit the Ford Shrader valve on the fuel rail?

I'm chasing a problem as well where as the vehicle (2001 sport 4.0 SOHC) will not start after shutting it off being up to operating temp. Once it cools down for 30-40 minutes, it starts right up and runs fine.
 






That's good Eric, give it the rag treatment. If you drop the tank, see if you have an extra FPR to swap in place of the original. That could be allowing some pressure back to the tank.

If the pressure does come up that fast, then the problem isn't a lack of pressure. That would hint at either the A/F ratio or the ignition signal isn't right at the start.
 












cnsheets,

The gauge I got from harbor freight was this one: http://www.harborfreight.com/fuel-injection-pump-tester-92699.html It had the correct fitting to connect to the schrader on my 4.0 SOHC.

I think my starting issue is separate from the fuel pressure issue. I am betting on a crank position sensor at this point.

Perfect, thank you. That's the one I was looking at. I replaced my crank position sensor two days ago. Same problem still exists, once it's up to temp, shut it off, it will not restart until cool. Changing the ECT now, and since I'm at it, changing the temp sending unit (o-ring was leaking anyway) and thermostat since it all needs to come out anyway to get to the ECT. If that doesn't do it, I'll run to harbor freight and get the pressure tester and test next time it doesn't start up. Hoping it's not a fuel pump, but starting to look like it.......
 






Interesting. On yours it won't start at all no matter what you do until it cools? I can get mine started every time, it just starts hard when the engine is warmer. It could have been sitting for 4 hours or 5 mins after shutting off at operating temp. It will exhibit the same condition; long crank time and rough stumbling start. I have to 'pump' the gas while cranking to get it to start easier and feather the pedal after it starts to keep it running. Once it is stable after a few seconds it runs like nothing is wrong.
 






Perfect, thank you. That's the one I was looking at. I replaced my crank position sensor two days ago. Same problem still exists, once it's up to temp, shut it off, it will not restart until cool. Changing the ECT now, and since I'm at it, changing the temp sending unit (o-ring was leaking anyway) and thermostat since it all needs to come out anyway to get to the ECT. If that doesn't do it, I'll run to harbor freight and get the pressure tester and test next time it doesn't start up. Hoping it's not a fuel pump, but starting to look like it.......

Stop there if that is not a 2002 or newer SOHC. The 1997-2001 sensors mounted on the thermostat housing are very very likely to begin leaking or not seal if you mess with them ever.

If you know it is leaking from either of those, don't touch them until you have purchased a newer thermostat housing, or the later model 2002+ parts to swap in their place.

Just trying to loosen them breaks the threads, they strip virtually every time. The only repair at that point is a new housing, which used to be $225+ IIRC.

The housing is actually two parts, top and bottom. The later 2002+ top housing can be used with the old lower, threads here have documented the parts and prices. The sensors are different, and those have to be bought to match the upper housing, plus the locking clips.

So be really sure that you have a leak at the sensors, before doing anything with them. If they don't leak, leave them in place. Those sensors generally don't ever go bad.
 






The temp sending unit that sends signal to the dash guage is definately leaking. My housing looks to be in excellent shape. None of the bolts were seized and once I pulled the clips on the sensors, they easily came out, probably a bit too easy. The sensors do not thread in, just an o-ring and clip. At this point I don't have any concerns about it going back together without problems. Guess we will see. Too far into it to stop now....I'll finish it up sometime in the next few days, not too concerned since I'm driving a 2011 Explorer anyway, the 2001 is going to my son.

I have to say, the design of this portion and the location of the sensors is ridiculous.....

oh, and its a 2001 SOHC 4.0 V6, manufacture date of 5/01

IMG_1849.jpg

IMG_1850.jpg

IMG_1853.jpg
 






Hot hard start

I had the same problem with my 4.0. Here's a little test you can try. Next time you've driven it a while, especially if it's warm outside, when you shut it off,uncap your gas cap to see if there is a lot off pressure built up. I never tried to re-start after I did this but wish I had tried now. What I did have to do was relieve the pressure at the rail which was more air than fuel with the pressure guage bleed valve. It usually took about a minute to do this. Then, it would start right up, no problem. Changed out my fuel pump, pretty easy to do in my opinion, problem gone. Also when I did a volume test on the pump, it only produced about 4 oz. of fuel in 15 sec. New one, about 16 oz. Hope this helps, it is easy to check.
 






Interesting. On yours it won't start at all no matter what you do until it cools? I can get mine started every time, it just starts hard when the engine is warmer. It could have been sitting for 4 hours or 5 mins after shutting off at operating temp. It will exhibit the same condition; long crank time and rough stumbling start. I have to 'pump' the gas while cranking to get it to start easier and feather the pedal after it starts to keep it running. Once it is stable after a few seconds it runs like nothing is wrong.

Correct, it will not start no matter what until it sits for about 20-30 minutes. It turns over fine, will give a quick initial sputter, than nothing....a couple times, it almost started, sputtered for a few seconds, then dies and nothing else for 20-30 minutes.

I have tried removing the gas cap to relieve pressure, did not help...
 






The temp sending unit that sends signal to the dash guage is definately leaking. My housing looks to be in excellent shape. None of the bolts were seized and once I pulled the clips on the sensors, they easily came out, probably a bit too easy. The sensors do not thread in, just an o-ring and clip. At this point I don't have any concerns about it going back together without problems. Guess we will see. Too far into it to stop now....I'll finish it up sometime in the next few days, not too concerned since I'm driving a 2011 Explorer anyway, the 2001 is going to my son.

I have to say, the design of this portion and the location of the sensors is ridiculous.....

oh, and its a 2001 SOHC 4.0 V6, manufacture date of 5/01
...



Excellent, the thermostat housing was updated in the 2001 model year. You have the 2002+ parts, much better.

How is the power of your truck, at high rpm? Usually a vehicle with a fuel pump that is not producing enough volume will have issues at high rpm, high loads etc. My 99 was okay except at top rpm,s, I got a lean code rarely. I had a leak in the rubber hose at the pump, a crack in the hose.
 






I never tried to start it after removing the gas cap. That was what made me put the fuel guage on the schrader valve the next time it would not start. After relieving the pressure for about 1 min., it would start. Sure was hot getting to that valve. Does your truck have the return line to the tank or is it the newer system that does not. I think '99 and up, it changed.
 






I am going to do a pressure check on a completely cold engine and fuel pump to see if it still wants to leak down. The more I think about it though, the more I am leaning toward a fuel pump replacement. Is the check valve built into the fuel pump or the regulator? Wherever this leak exists, it has to be the source of all my problems.

If the pressure bleeds off quickly when the engine is warm, could it be that the gas in the fuel rail boils to a vapor due to heat soak and causes starting issues because of this? High system pressure obviously changes the boiling point of the fuel. Once the engine cools down the vapor comes back to a liquid state and there is no more starting issue. :dunno:
 



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Well, I hooked up the gauge to a complete cold engine that had been sitting all night long. It is around 40 degrees F outside. Not a single drop came out of the schrader. Pressure was zero (zip zero nada) psi.

I turned the key on, fuel pump primed the system and the pressure immediately shot up to 60psi. The priming cycle ended and the pressure started dropping pretty quickly. It was down to 20psi after about 30 seconds. Having never turned the key off, I moved it to start and the engine began cranking, the pressure jumped back to 65psi and it fired right up immediately. Crank time was normal.

I can only assume that the issue is what I described in my previous post. Higher temps result in vapor inside the fuel rail at these low pressures.
 






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