Fuel Pressure regulator

[SA-Xplorer]

My '96 X is still chugging and dying after driving in the heat, at slow speeds, it seems once the fatal starvation sets in, even if I am on the open road at reasonable speeds (60mph) with speed cruise on, it still eventually dies.

After sitting for about 10min, it seems to find itself again for a while, but the distance travelled after dying is directly proportional to the length of time it stood recovering.

I will be checking fuel pressure when I get my guage on Wednesday. (I presume I can just fit it to the pressure release valve in the engine?)

I was wondering if the 96 4.0L OHV has a Fuel pressure regulator.

In essence I am trying to accumulate all the options to check so that when the death chug happens, I am prepared to test all options.

Thanks Ralph

 

[SA-Xplorer]

bump?

 

[2000StreetRod]

Return fuel system

Your vehicle has a return fuel system with the vacuum sensitive fuel pressure regulator (FPR) mounted on the fuel rail. When you receive your fuel pressure gauge measure the pressure with the engine at idle (strong vacuum) and then again with the vacuum line to the FPR disconnected (weak vacuum). If the FPR is working properly the fuel pressure should be significantly greater with the vacuum line to the FPR disconnected.

 

[SA-Xplorer]

I fitted just fitted the fuel pressure guage. I came with a long coiled length of thin copper wire and two brass fittings on the ends. I had to make a small mod to fit it to the test valve next to the FPR. I checked for leaks from the fittings and there are none. I read 0 bar when I switched the ignition on. Just the pump whirring as it filled the line.

I then started the engine and let it idle. It came up to 1.8 bar. I then revved it and it settled at about 1.95bar. (Just under the 2 bar mark.) This by my calculations is about 28psi, which does not seem right I think. I revved it to 3000 RPM and the guage never moved. I WOT 'd it a couple of times and the guage was rock steady.

This was before I started up my PC to find your reply.

So now I will go back out into the night and find the vacuum tube. I only found one small little tube. I will presume this is it.

As to my idea that it might be the FPR, my logic is this.

I have bought my X with some mods and some bits missing. I am sure it had some sort of heatshields over the outlet manifolds, which it does not have anymore. After I have driven for a while, when I open the hood, the engine feels seriously hot even though the temp says not. I was thinking that maybe the FPR starts to get hot and the diaphragm ( I presume that is how it works) gets too hot and starts to stretch and fail.

I had a volkswagen with this problem with the diaphragm fuel pump. If it was hot and stood, the heat would freak out the pump and it would not work. As soon as I had doused it with enough cold water, it would work again.

My idea to reduce the heat under the hood is to wrap the oulet manifolds with ceramic tape to contain the heat. Once I find some suitable material for heatshields I will fit this as well.

Thanks for the reply. I will check out the vacuum tube and reply shortly.

 

[SA-Xplorer]

So! I switched on the ignition and the pump chirped and pressure came up to 1.8bar. I started the car and the pressure stayed at 1.8 bar at idle. I disconnected the vacuum pipe and the pressure shot up to 2.4 bar. I revved it, WOT'd it briefly, ran at up to 3500RPM constant for a couple of seconds and no change from idle. 2.4bar.

Then I fitted vacuum pipe again. (checked if it was sucking first and it was) Immediately the idle faltered for a moment and then settled. When I rev up slowly to 3000 and 3500RPM the guage moves slightly but stays at 1.8-1.9 bar. When I WOT it, it blips up to 2.4bar momentarily and then drops back to 1.9bar at revs. Idle slides back towards 1.8bar.

So what does this mean?

As far as the pressure is concerned, according to the service manual pressure should be 65-68PSI. THat is about 4.5bar. My guage may be reading wrong. I will find a friendly mechanic and lend his (or her) pressure guage to check. But the relative pressures should neverthrless say something.

 

[SA-Xplorer]

On further study it seems that Ford call the part i was fiddling with the fuel pulse dampener. It sits on the fuel rail just right of the oil filler cap. The fuel pressure regulator appears to be in the tank on the fuel pump assembly. The 5.0L has a fuel regulator in the engine bay according to the service manual. But the manual is written and illustrated with very small pics and so difficult to understand and to orientate myself when looking for parts on the engine.

I would be interested to know what the acceptable fuel pressure should be for the OHV engine. And how does more or less pressure affect MPG and power/torque.

 

[2000StreetRod]

regulator vs damper

Unless one of the modifications to your vehicle was to advance to the newer returnless fuel system, you are comparing the wrong information to your vehicle. In 1999 the Explorer switched to a returnless fuel system with the fuel pressure regulator in the tank and a fuel pressure damper on the fuel rail. The fuel pressure for that system is always about 65 psi. See the following thread:
Fuel pressure test procedure

The 1998 and earlier Explorers utilized a return fuel system with the vacuum controlled fuel pressure regulator mounted on the fuel rail.

Fuel pressure at idle with vacuum hose attached:30 to 45 psi
Fuel pressure at idle with vacuum hose detached:40 to 50 psi

Your fuel pressure at 3,000 rpm should be greater than at idle with vacuum hose attached and less than at idle with vacuum hose detached

Has it been more than 30,000 miles since you replaced your fuel filter? It could be clogged and causing your fuel pump to overheat and thermally shut down.

 

[SA-Xplorer]

AH! The service manual I am working off is 1996 to 2000 Explorer and mountaineer. The eninges it covers are 4.0L OHV, SOHC and 5.0L. So I am looking at the fuel line on a later system there.

Nevertheless, no conversions here, definitely a return line system.

My pressures work out to 27.5 PSI with the vacuum on and 35 PSI with it off. There is no major difference between idle and 3000RPM, maybe 8 or 8 PSI....unless that is significant.

If the pressure is low, why? Do I need to reset something or do I (...he said in fear!!) have to replace the fuel pump?

Now that is interesting. I dont know when last the fuel filter was changed. I did notice that the last time it died, after a few minutes I tried to restart and it would not. Then not 2 minutes later I switched on the ignition and the pump was whirring away like normal. So as you say most probably fuel pump overheating.

I will scour South Africa for a filter and report back once done.

Thanks 2000!

EDIT:

I have found a filter thankfully and amazingly it was at the dealership and at a reasonable R $18. I will collect on Friday and fit Saturday.

 

[SA-Xplorer]

Sadly, it was the wrong filter and the right one landed up costing $70! When I got under the X, I found that there was a mod done to the X and an inline BMW filter made by Pierburg was installed just in front of the filter. I changed teh filter anyway, but kept the old one as it still seems new.

Pressure is no different from before. However, my brother made a comment. What if the fuel tank is creating a vacuum and not letting the air replace the fuel used. Would this not cause a problem?

As I cannot source an original tank pump locally, I a trying to get a 45PSI BMW inline pump to improve the pressure. Any suggestions to the contrary?

 

[SA-Xplorer]

Chugging X

I thought an update on my chugger would be in order.

I have finally localised the reason the X dies....fuel starvation. However it is not the usual cause.

Someone in their infinite wisdom modified the X and put an inline fuel pump for a BMW. However the inline pump only pushed 1.9bar regulated instead of the required 3.0bar.

I made a 700mile trip into Mozambique just north of South Africa and broke down along the way...same story. We then chugged into a gas station and the answer presented itself. As soon as I filled up the X was fine.

So evidently there is a clogged in tank filter or something like that which, when the tank gets to half, starts to slow fuel flow to a dribble.

I also noticed that there is a serious vacuum formed in the tank which causes trhe pump to over heat and the diapragm does not pump properly. I put an ice block onto the pump for 10-15 min and it works again.

My remedy will be to install a larger Bosch inline pump that can do 3.0 bar regulated. I will also be dropping the tank to find out what is causing the blockage as well as fitting an additional inline filter before the pump to catch any loose crud froim the tank.

One question I would like an answer to.. What effect does a lack of fiuel pressure have on mpg and power/torque?

 

[budwich]

likely poor gas mileage and lower power as the gas is not "aspirating" enough (ie. "nice spray") resulting in poor firing and resulting weaker power.

 

[SA-Xplorer]

I thought so. I am looking forward to getting the pressure back to spec next weekend and i will report back.

 

[j.lee]

I'm not a physicist, but I'm gunna hafta go ahead and advise that you do not do douse anything on your car with cold water. Cooling something down, or heating it up too quickly can easily result in serious damage. If you've ever poured warm water on your windshield after an ice storm, you'd know this. It needs to be given time to slowly cool down. I also have a 1996 4.0 OHV that I am about to change the pump on. If you can:
1.) attach a 1/2 inch nylon tube to the FPR so that it forms a seal
2.) pinch the tube shut
3.) block air from entering the return fuel line (I used my thumb b/c the pressure was already very low)
4.) watch the pressure
-you should see a sharp rise in fuel pressure if the FPR is in fact failing. I tried this test earlier to find out that I have a bad fuel pump. Needless to say i will be without transportation.

 

[SA-Xplorer]

Thanks for the insight J!

Well seeing as it was aluminum (the pump casing) and it was around 100 degrees, I would have to have sat there for the better part of a couple of hours and that would have been nasty seeing it was the middle of the day....mad dogs and Englishmen...! So I took a short cut.

I did do the initial test to see if it was the FPR. I had 1.8-1.9 bar at idle with a blip up to 2.4bar at WOT with the FPR inline. The FPR bypassed was 2.4 with no changes. The pressure unregulated should be about 4- 4.5 bar unregulated and 3 bar regulated.

So the pump is not producing the necessry pressure and or the fuel tank is increasing the vacuum and causing the poor ol' pump to over heat as it tries to suck a pea through a straw.

I will be tackling my X on the weekend to see what is causing the blockage in the tank and fitting the new pump and additional filter. I will let you know how it goes.