Help diagnose engine problem

[Brian1]

For the past month and a half my 91 has been missing under acceleration (jerking movements) in all gears and at all speeds. When I tow my trailer it will sometimes make a popping noise from the exhaust. It also overheats (needle to the right of straight up) when going up hills or under heavy loads. It does not always happen but most of the time it will. It does this with a hot or cold engine.

In February I replaced the upper and lower intake gaskets and the valve cover gaskets. I also put in a new t-stat and fan. The explorer ran great for about 3 or 4 weeks then began to have the missing problem.

The following is what I have replaced recently:
Fuel filter (new)
Water pump (new)
Spark plug wires (splitfires - 5000 miles old)
manifold gaskets (700 miles old)
O2 sensor (8000 miles/ 18 months old)
muffler (5000 miles old)
K&N filter cleaned 1000 miles ago
MAS cleaned 1000 miles ago and rechecked recently

The following is what I have checked:
Spark plug wires are not arcing
Spark plug wires have approx 500-600 ohms resistance per foot and no cuts or kinks
PCV system works correctly
Spark plugs are still good w/ correct gap but are powdery white looking meaning too much heat?
At idle, vacuum tree has a steady 16 in. of mercury vacuum
Reving from idle to approk 2500 the vacuum goes down 2-4 inches then immediately rises to around 20 inches of mercury at the vacuum tree.
Engine idles smooth
Scanner gives codes 67 and 57 with key on engine off
Scaner gives everything okay codes with engine running

I dont want to replace the spark plugs yet until the problem is found because I dont want to damage the new plugs with the powdery white glaze that is forming.

My cat. converter smelled like it was going bad about 6 months to a year ago but the smell went away. It passed emissions after that. Recently I can smell the egg smell inside the cab but it is very faint and dont know if it is mine or someone elses. Could this be part of the problem?

Another member mentioned it is most likley a vacuum leak but from the vacuum measurements I took and what I have read it seems normal.

Could it be that the injectors need cleaning, there could be some carbon that may be blocking them after I put the manifold back together? (I did clean alot of the carbon out when I had it apart)

Also I found out recently that the octane shorting bar was unplugged by the fuse box under the hood (if it is the little grey and black connector). It has been like this ever since I bought it so I dont think that would make a difference.

Could the timing be messed up causing it to overheat and cause the missing and popping under load and acceleration?

Does anyone know what it could be or how to fix it? Thanks. I need to get it fixed soon so I can do some wheeling and not overheat or damage the engine!

 

[mrboyle]

From your discription it sounds like you are experiencing a lean condition. White plugs, running hot, smell from cat, popping (actually a lean miss) are all symptoms of running extreemly lean.
Usually injector problems will cause rough idle (since typically only one or two injectors develop problems) so I don't think there is any carbon blockage.
My first thought would be a vacuum leak. Have you checked the intake tube between the air box and the throttle body. I have seen several that have ripped in the bellows allowing unmetered air to enter the engine and cause lean conditions.
Another thought would be to check the fuel line (high pressure side) for any kinks or damage. If its ok try testing the fuel pressure.

 

[Alec]

Yup, I was thinking fuel pressure regulator. Also, you should replace your radiator cap with your tstat, did you?

 

[Brian1]

Okay I will check the air intake and see if it has any cracks or rips. When I replaced the fuel filter a week or 2 ago I looked at the fuel lines and they looked okay. I will check again.
Alec, no I didnt replace the cap but when I make a run to the parts store I guess i should get one anyway.

So I should check the fuel pressure? Ill do a search for that later. That is on top of the manifold correct?

Thanks guys.

 

[tONYB]

Thermostat?

 

[mrboyle]

Actually Alec, I was thinking more along the lines of lack of fuel pressure due to kinked pressure line or tired fuel pump. Seeing as the pressure regulator is on the end of the fuel rail oppisite the pressure inlet, I don't see how a FPR could restrict fuel pressure.
Brian, did you check the fuel ilnes near the engine for damage?

 

[Brian1]

Not yet, I havent had time. I will try to look tomorrow and try a few other things.

 

[Alec]

I thought the FPR could stick either way, either limiting fuel or dumping too much in?

 

[mrboyle]

Originally posted by Alec
I thought the FPR could stick either way, either limiting fuel or dumping too much in?

I have never seen one restrict fuel (but anything is possible).

 

[go off road]

BTT

have you done block check? Try some injector cleaner and try differt gas and chenge your plugs back too MortorCraft platums

 

[Brian1]

Just got in from checking it. Fuel lines are good - no kinks, etc. I sprayed carb cleaner around the manifold and heard no surge in the idle. Also inspected the intake tube and no signs of cracks. Inspected the line from the oil filler to the intake tube and it was good as well. I have not done the fuel pressure check yet mainly because I dont have a gage to do it with. I checked the spark plug wires again and no arcing, wires are all routed with clip on spacers and all go to the correct cylinder. I did do a check on the FPR as described in an article on the explorer maintenance page and it checks out okay.

Wade, could the plugs alone cause the problem? I dont want to buy new ones then have them turn powdery-white like the current ones.

Different gas shouldnt be a problem. I have been running the same grade since I bought it and there has been no probs untill now. Also have gone through several tanks since the problem and there has been no change.

Would plugging back in the octane shorting bar do anything to help the problem? It has also been unplugged since I bought it. (If Im looking at the right plug near the fuse box)

Thanks guys.

Edit- I plugged the octane shorting bar back in and one of the engine codes went away (octane adjust circuit grounded) I will drive around a little with it plugged in and see if it makes a difference.

 

[Brian1]

fuel pressure

I checked the fuel pressure. At idle it is 32 and with the vacuum hose to the FPR off it was 39. After shutting it off the pressure rose to 38 from the 32. It stayed at 38 for 10+ minutes. Key on engine off was 38. With the engine idling and the return line from the FPR pinched the fuel pressure remained constant at 32.

I took the octane shorting bar back off because the engine started knocking when accelerating.

 

[Brian1]

Status Update

I replaced the plugs with motorcrafts and the hesitation and missing seems to be gone. It has more power but it still gets hot when going up hills. I took it to the mountains Sunday and it got to the L in Normal when going up the mountain and it stayed there for a while. I replaced the radiator cap after that and so far so good but I havent had a chance to put it under a heavy load yet.

I do hear an air leak noise from underneath the driver's fenderwell but it is faint and it can only be heard from under there. Is this normal or is there any vacuum lines around there that could be broken? I cant pin point it.

 

[takaminegenie]

That air leak may be coming from your brake booster grommet, they have been notorious for leaking after 100,000 miles or so on all the fords i have had.