'98 Exp. SOHC - Rough Idle / No Power **Big Mystery**

[Carguy3J]

Ok, so I'm stumped on this one. I would consider myself fairly good at diagnostics, but this one has me ( and apparantely a number of Ford master techs, and others, stumped)

Not mine (yet???- The owner is fed up, and I might be able to buy it cheap as is, but I;m a little scared of this problem), so I'm relaying what I was told regarding previous/recent work and attempts to diagnose:
'98 Explorer SOHC/Auto/A4wd/4dr about 129k on it

Idle is really "choppy"/rough- gets a little better after warm up, but not much. It's not "surging" like a bad IAC type of thing, it maintains a fairly steady rpm, but with bad missing

Under load (uphill) or under heavy throttle (really, anything more then just enough to barely accellerate), it is clearly bogging/missing/ falling flat on its face. It will accllerate, but not at a normal rate, and it "ain't" happy about it. It is acting like a bad cat (but keep reading before jumpimg to any conclusions)

There is also a "ticking"/pinging sound coming from somewhere around/under the engine area, even at idle. I can not seem to audibly localize it. Sometime it sound like it's on the driver side, then sometimes on the passngr. Sometimes it seems to come from the top of the motor, then not. It kind of sounds like a small exhaust leak. I don't feel that it sounds like a rattling chain. Although, it does sometimes sound like a lifter/rocker tick/tap.

The truck is in relatively good shape. The current owner ( a used car dealer - friend of a friend) has had it to several independent repair shops, as well as a Ford dealer. No one can fix it, although they've thrown a lot of a parts at it.

To be clear: THIS PROBLEM EXISTED BEFORE ANY/ALL WORK BELOW WAS DONE, and continues to exists w/o any improvement.:

1.) They first suspected it was a fuel issue, so FUEL PUMP/FILTER were replaced. No change

2.) I was told there was an issue with the TRANS, so a rebuilt unit was installed - obviously no change

3.) Ford recommend new cats, so (2) NEW OEM REPLACEMENT CATS were installed - No change- although Ford is now stating that they believe tht one of the NEW cats is defective and causing the problem. I'm skeptical of this. Has anyone heard of this happening?

The shop has NOT removed/unbolted the new cat(s) to test, but I was told they removed the upstream O2 sensors, with no change (this would have provided an alternate escape route for the exhaust if the cat was plugged. I doubt that the hole(s) is big enough to make a difference though. I suggested that the cats be unbolted at the manifold and driven and/or tested. Thoughts?

4.) It has a recent tuneup (PLUGS/WIRES) I suppose the firing order could be wrong? But this was done by a professional shop, and afterwards a Ford dealer tech(s) also looked at the truck. Sure, it's possible. But I think this is an unlikely cuase at this point. Thoughts?

5.) I was told that the MAFS was cleaned. No change. They then installed a NEW MAFS, no change, so the old one was put back on.

6.) TPS was either tested good or swapped with a new/known good. Not 100% clear on which. - Again, no change.

7.) Was told EGR VALVE was tested good.

8.) Dealer said he was told that there "might" be an INTAKE LEAK. I tried spraying brake cleaner all around the intake (upper/lower), the throttle body gasket, and any other potential air leak sources. There was no change in idle speed or quality.

9.) I was told that a COMPRESSION TEST was performed, and all cylinders showed "normal". I do not have specific numbers.

10.) I put my Snap-On scanner on it, and got no KOEO codes, no KOER codes. The onyl code I got (sorry, didn't write down the number) was a "memory" code : Bank 1 lean

Unfortunately, the OBD2 monitors were "not ready", so I believe the dealership had cleared everything about an hour before I looked at it, so the "no codes" may not be a true statement, although the owner indicated that there had been no "Check Engine Light" on.

11.) Owner also said he "thinks" they replaced the CRANK SENSOR somewhere in all this.

12.) Both OIL and COOLANT looked clean/the right colors, so no signs of a bad HEAD GASKET.

13.) I did a "wiggle test" with the engine idleing, on several major sensors, with no changes. (TPS/MAFS/DPFE/IAT)

My thought/ideas:

1.) Unbolt/test cats, even though new ( I mean brand new, still shiny)

2.)Leak @/ cracked exhaust manifold? Although it would explain the bad idle, wouldn't really explain the bog under load ( really "feels" like a bad cat)

3.) I didn't have a fuel pressure gauge w/me when I looked at it. Maybe their first thoughts were right, and it is fuel related? Perhaps perform a fuel pressure test? I would like to check for suffecient volume as well, but I'm not clear on how to accomplish that without making a big mess. Stupid question, I know, but any suggestions for checking fuel flow volume? Anybody know the specs?

Maybe there is a kinked line somewhere, or a bad FPR?

4.) Double check correct firing order on wires? (but I really doubt this is it)

5.) Pressure test the cooling system to verify no possible head gasket issues, along with repeating the compression test?

6.) What should the MAP/BARO reading be? In NJ, above sea level, but not in the "mountains". Scanner showed 148hz.

For now, this is all the info available. I can NOT run to the truck and perform additional tests, as it is not mine (yet?). I'm trying to get a reasonably good idea of what I might be getting into if I buy it.

I'd appreciate some ideas/thoughts from anyone who knows what they are doing. Thanks guys.

[my98nnj]

A clogged cat or exhaust system isn't going to make it actually misfire.
The cats have been replaced, I think you can rule out the exhaust.

The only thing I think you have left is to check the jackshaft timing chain to see if it's jumped a tooth. That would definately allow it to run, but very poorly.
We all know how famous the SOHC motor is for it's timing chain issues.

[2000StreetRod]

I would start with the CMP sensor. The PCM uses the CMP sensor output to determine when to fire the injectors. If the injectors are not pulsed when the intake valve is opening the fuel charge will be "stale" when the valve does open.

You mentioned a pinging. The SOHC utilizes a knock sensor. Any continuous mechanical noise can be misinterpreted as knock and the PCM will retard the spark advance. This can easily be checked with a scanner that can measure knock retard.

I doubt the primary timing chain has slipped. I was unable to "slip" my chain with my hands even after removing the tensioner and the guide.

I would also check the CKP sensor again. The symptoms are similar to those from a bad CKP sensor.

[bluestream1]

Have the o-rings o the intake manifold been replaced with the new up-graded blue ones?

[CDW6212R]

That is interesting. I'd agree with Dale to check the CMP and the ignition timing(knock sensor).

Check this other thread and comment about your noise compared to his;
http://www.explorerforum.com/forums/...3&postcount=51

The fuel pressure should be 62-65psi ideally, at all times. I doubt the head gaskets are bad, the SOHC evidently has great HG's.

I would suspect the plug wires first for a miss, even new wires can turn out to be bad.

If the engine did have a lean code like 0171 or 0174, that can be several things, from a poor fuel pump to the upper intake gaskets.

I doubt the chains have jumped also, if that did happen you would have much more noise than you do.

In that other SOHC thread, the balance shaft was worked on. I didn't read much of that, but I would wonder if the balance shaft is in time, that could make an imbalance with an odd symptom. Good luck, it sounds fixable, the engine stuff would be the most trouble.

[Vargas]

Do you know the timeline for when all this work was done? Is the lack of power so bad that it is not being driven much or at all?

Could this be something as basic as contaminated fuel, clogged fuel tank pickup, clogged or pinched fuel line?

[budwich]

hopefully your "friend's used car friend" IS a friend..... sounds like $1 deal. run data might give you some ideas but it sounds like a timing issue like associated with the "normal" sohc "personality" when it is about to go "psycho"... :-)

[joshsdaddy2006]

Did you ever figure out the problem? I have a 98 that is doing the exact same thing, and have checked everything you have to date.

[Carguy3J]

Sorry for not "wrapping this up" Thanks to everyone who tried tried to help.
No, I never figured it out. It was too much of a gamble, and I'm not in a financial position to risk such a potential disaster. With the potential of bad/slipped timing chains, the price just wasn't right.

[Rockstarenergy]

ahh ive got the same problem in my 97 im thinkin its my exaust not sure but i know what you mean by the lack of power 90% of the time my gas is pinned to hit 55 =\