1998 Explorer SOHC Fuel pressure spec

[fastkurve]

Hi everyone,

I went through some threads with the search engines for the last 30 minutes but can found what I am looking for...

Can somebody tell me what is the fuel pressure spec for the sohc engine.

I did verify the pressure this morning and ended up having 35 psi with the key on and the same with the engine running. If I accelerate quickly, the pressure drops below 30 psi and if I keep the engine speed at 2000-2500 RPM, the pressure catched up to 40 psi.

I read the write up thread that Glacier made a while ago about fuel pressure, but I did not see details about pressure behavior under acceleration....and the hread was made from a first OHV engine, might having different spec for my engine.

Thanks for responding

Fastkurve

 

[Turdle]

Actually-
I think it should be around 40 psi, and climb to 43-45 psi while accelerating.Are you disconnecting the vacuum line for the "static" reading?

Do you smell gasoline in the fuel pressure regulator vacuum line?

Fuel filter?

 

[Mustang4mikey]

i believe 35psi is correct. I had a gauge on my Mustang that constantly read 35 and went up as i have accelerated. Also, your fuel pump may be running out of steam. In time, Fuel pumps dont pump as much fuel and when they were new.

 

[Turdle]

i believe 35psi is correct. I had a gauge on my Mustang that constantly read 35 and went up as i have accelerated. Also, your fuel pump may be running out of steam. In time, Fuel pumps dont pump as much fuel and when they were new.

It should be above 40psi in explorers up to 99,which is when they switched to a return less system and bumped it to 60 psi

 

[scucci]

from the service manual: Specifications - Pressure
Fuel Pump 30-45 psi

Scucci

 

[fastkurve]

from the service manual: Specifications - Pressure
Fuel Pump 30-45 psi

Scucci

Thanks for the info, that's what I was looking for. Did it say in the service manual that the pressure should hold under acceleration or it could vary?

Fastkurve

 

[CDW6212R]

The pressure regulator takes vacuum and raises the pressure a good 5psi or so. That's why you read of several pressures, pull the vacuum line to test it both ways.

The pressure shouldn't drop too much with throttle, that's what you worry about. My 99 had 52-55psi at idle, and dropped below 50psi just winging the throttle in park. I had some kind of leak, my thought was the rubber lines at the pump. With a whole different used pump etc. I had 62psi at idle, and no drop with throttle use.

The pre-99 Fords should need about 35-42psi, don't worry unless it gets outside of that. Regards,

 

[fastkurve]

Thanks for your advice CDW6212R,

That was exactly what I was wondering

When idliing, FP is 35 PSI and quick throttle move got it down 28-29 psi and recover to 35 PSI a while afterwards.

I also noted that the pressure goes up with slow throttle accel. at 2,500 RPm approx FP reads 40 PSiI I also checked the vacuum line,it does not smell gas, so I figure that the regulator is fine.

Fastkurve

 

[CDW6212R]

Well does the pressure jump up 5psi or so when the vacuum line is disconnected? It should, if not I'd do the regulator. If it does jump up then the regulator is fine, and the pump or a leak is the problem.

 

[fastkurve]

Well does the pressure jump up 5psi or so when the vacuum line is disconnected? It should, if not I'd do the regulator. If it does jump up then the regulator is fine, and the pump or a leak is the problem.

So if I follow you correctly, when at idle, the FP should not change by plugging unplugging the vacuum line at the regulator? Is it correct then if it goes up by increasing the engine rpm?

sorry for asking so much questions?

Fastkurve

 

[CDW6212R]

No, when the vacuum line is pulled off of the regulator, the fuel pressure should rise. The vacuum from the line is supposed to be there for the regulator to control the pressure. Under most conditions the engine will have a lot of vacuum, and the pressure thus will be about 35psi most of the time.

Under high throttle the vacuum drops inside the intake manifold, which is where the vacuum line goes to. That's when the regulator sees the vacuum drop, and raises the pressure for the higher load.

 

[fastkurve]

Edited to changed the picture link.....

Ok just finished checking the FP. As said before, with vacuum line connected 35 PSI, with vacuum line disconnected 40 PSI.

I also removed the six spark plugs to check their condition (combustion) and the passenger side ones are much more whitish than the ones on the driver side...here's a link to look at the worst ones of the passenger side

[/url]http://s296.photobucket.com/albums/mm174/Fastkurve/?action=view&current=whitishsparkplug.jpg

What should I understand from this? The engine does have a rough idle. I can drive smooth and easy, has a lag when I floor it and I can feel a jerking motion when coasting at 35-40 mph.

The vacuum reading is bouncing steadily from 12 to 14 "Hg.

Spark plug and leads were replaced about 10 days ago, compression reads 120 PSI at all 6 cylinders(has rechecked all of them once again tonight with another gauge, just to make sure) fuel filter was replaced last fall and I redid the 00M12 oring stuff last week. I washed the top of the engine and all vacuum port with carburator cleaner, no idle change so ever & I scanned the computer with two different devices (Autotap ans SCT handheld tuner), no code.

What would you proposed next? I'm clueless.......

Fastkurve

 

[CDW6212R]

That tells you that the regulator is okay, it runs the proper range of pressure. The fuel pump still could be weak, you mentioned before that the pressure dropped at times? What does it do if you wing the throttle open quickly at idle? You would like to have virtually no drop in pressure under that kind of no load condition. It should go up with the regulator connected, and with the line plugged it shouldn't drop much at all below the 35psi at idle.

How does it act while driving it, the tip in response and WOT power curve? Does it fall on its face completely, or buck/surge?

 

[fastkurve]

"you mentioned before that the pressure dropped at times? What does it do if you wing the throttle open quickly at idle?

Did check it again tonight while the gauge was hooked up and I not see a pressure drop as I saw last friday night when I first checked it

You would like to have virtually no drop in pressure under that kind of no load condition. It should go up with the regulator connected, and with the line plugged it shouldn't drop much at all below the 35psi at idle.

FP goes up while opening throttle with the regulator connected and does not drop mcuh under throttle opening.

How does it act while driving it, the tip in response and WOT power curve? Does it fall on its face completely, or buck/surge?

When flooring it, just feel an hesitation for 1-2 seconds, then starts accelareting slowly, then at 3000-3500 rpm, accelerates normally under wot. Under normal condition ,normal start from a stop or light, just drive fine, bucks/jerks when coasting at 35-40 mph afterwards...

Fastkurve

 

[CDW6212R]

That does not sound like a fuel pump symptom at all. The fuel pressure is a good diagnostic tool to eliminate the common pump issue. Often you end up finding an ignition problem from things like the plugs or plug wires. Also with the many vacuum leaks that have happened on the 4.0's you have to consider those also. How old are the plugs and plug wires, those are easier to do than hunting a vacuum leak in an intake gasket? If they are really new then I'd wonder about the MAF and TB cleanliness, and then the upper intake gaskets. Who did those intake gaskets, which should be part of that TSB kit?

 

[fastkurve]

Also with the many vacuum leaks that have happened on the 4.0's you have to consider those also.

By spraying carburator cleaner (previously tried wuth a propan bottle) I was looking for possible vacuum path, no luck.

How old are the plugs and plug wires, those are easier to do than hunting a vacuum leak in an intake gasket?

Brand new from Ford

If they are really new then I'd wonder about the MAF and TB cleanliness, and then the upper intake gaskets.

MAF was cleaned, that was one of the first thing I did about 2 months ago..


Who did those intake gaskets, which should be part of that TSB kit?

I did it myself

Fastkurve

 

[rbyerman]

Correct Fuel Pressure

guys I had a similar problem with my 98 SOHC 4.0. Under easy driving it was fine. Under hard accel it would loose power big time. if I backed off the pedal to about 3/4 open it would pick back up in power. This got worse and worse over time. Check engine light was on and codes were p0174 and P0171 for many months. I finally found out the fuel pressure was 26 psi. when I unhooked the FPR it jump to 33. It should have jump to 45 or 50 psi. I changed the fuel pump (which was installed new 1-1/2 years ago) and the problem is gone. It sounds like this dudes fuel pump is going bad.

 

[fastkurve]

I do not have any recorded codes and the check engine light never came ON...

Fastkurve

 

[CDW6212R]

My 99 was throwing a P0171 or P0174 code rarely, once a day or two. The slightly low fuel pressure was not bad enough to make a code most of the time. Your fuel pressure is good enough at idle from your tests. If the power dropped off at the highest rpm's then I would think pump. Your issues are evidently at various rpms and conditions. That doesn't point to a fuel pump.

 

[fastkurve]

Hi Don,

Keep investigating my truck poor idle, low vacuum (10-12"Hg) and ended-ep talking to a guy who prepare motor for drag-stockcar racing, asking him for his opinion.

Reporting him the details of all I've done (compression at six cylinders @ 120 PSI, vacuum @ 10-12"Hg, lost of power during normal driving, poor idliing, no codes, new plugs/wires, redid the manifold packing, engine does not consump oil, plug about all vacuum ports at the engine/intake plenum,checked for vacuum loss, still no luck!), he felt that the cams might/probably are not timed anymore correctly due to timing chains stretch.

His theory is making sense to me.

The truck has 145000 Km (90K miles)

Does it sound right to you?

Robert