Runs rough, dealer service says 'old'

[rkcameron]

Had two diagnostics, 1st said PCM O2 side no voltage coming out. took to dealer with replacement PCM, said not computer; still running on original. 2nd dealer diag said truck old, timing belt is my ping kinda noise, also said compression checked twice cyl 2 and 4 gave low then normal value. One of forum posts suggested coil pack and one lower intake manifold gasket kit for TSB M0012. I told dealer about M0012, it was not mentioned in the report.
Start truck idle searches then runs rough with maybe 15 mpg from about 20.
went from 350 miles per tank to 225. Need help here guys. have replaced parts per mechanic directions, and done tuneup, plugs, wires, seafoam, and intake cleaning.

thx
rkcameron

 

[TourGuide]

Year - ?

Motor - ?

Miles - ?

 

[Explorer75]

We need more info.

Like if you just bought this truck, if you have done a tuneup.

I would start with the most basic:

Oil and filter change
Spark plugs
Air filter
Fuel filter
Maf clean up

Then

Ignition cables
Coil pack
Seafoam

 

[Tech By Trade]

How much lower is lower than normal.

 

[rkcameron]

reply to first 3 posts

1998 4.0L SOHC 171000 miles
mileage 20 down to 15. don't know how much lower compression, sorry
I bought it 12 or 13 yrs ago. done a couple of tune ups, one was couple months ago. replaced plugs, wires map sensor, regular oil chg, air filter reasonably clean, replaced fuel filter and fuel pump. and seafoam 1 or 2 tanks ago. did intake cleaning even with brush and scrubbing, also they did the can and smoked up the neighborhood.
have not done coil pack yet.

 

[Tech By Trade]

Sounds like you are just randomly trying to change parts to fix the issue. I would suggest some serious trouble shooting. Start by picking up a cheap compression tester and check the cylinders. The highest and lowest should be around 15% difference. any more and there is issues.
On my old 350 Chevy, If the cylinder is bad like you said, you could try and put a table spoon of oil in that cylinder, and retest. If the compression goes up, your rings are shot. If it stays the same the head is the issue.
Change that bad O2 Sensor as well.

If its the timing, you need to pull the motor to replace the chains. I am currently in the middle of the process on an 07. It sucks, real bad. Not a lot of money (about 200 into it so far) but a major time suck.

 

[Flag Gibby]

1998 4.0L SOHC 171000 miles
mileage 20 down to 15. don't know how much lower compression, sorry
I bought it 12 or 13 yrs ago. done a couple of tune ups, one was couple months ago. replaced plugs, wires map sensor, regular oil chg, air filter reasonably clean, replaced fuel filter and fuel pump. and seafoam 1 or 2 tanks ago. did intake cleaning even with brush and scrubbing, also they did the can and smoked up the neighborhood.
have not done coil pack yet.

rkcameron, not that we cannot help you figure it out, but you really need to post over in the correct section for your generation in order to get the guys that work on your years of explorer all the time. I am sure that someone over there has run across this before.
On another note, check the voltage coming from the coil pack on the two cylinders that the shop said had low compression it could be the coil pack but no need to replace it unless the voltage indicates that it is bad.

 

[rkcameron]

sorry, but, I am not randomly changing parts! I am going by what the mechanics have told me was bad. the tuneup and map sensor were necessary by either mileage or they were cracked somehow and we spotted the break.

 

[2000StreetRod]

no timing belt

There is no timing belt in the SOHC V6 engine. The camshaft timing is maintained by chains. What were the compression values? If the compression is low for all cylinders on both banks then the crankshaft to jackshaft chain may have slipped due to a broken primary chain tensioner.

The newer tensioner is more robust.

If only one cylinder in each bank has low compression then it could be due to blown head gaskets, cracked heads, sticking or worn valves, broken valve springs, worn piston compression rings or valve seats. How many miles are on the odometer?
If the upper and lower intake manifold gaskets have never been replaced then I would start there.

 

[rkcameron]

it has 171000 miles. the dealer only said on the first compression reading it had a lower value on cylinders 2 and 4. then rechecked and all were normal. the intake manifold was replaced when I bought it in 2002. thanks for the pics! sorry for mixing belt with chain.
I have an appointment with a mechanic next Thursday. But, I will looking in my records for anything I can answer. thx for helping. what is the possibles for a clinking light metal on metal sound, doesn't change with rpms that I can tell.

 

[Turdle]

I merged your threads into one. This one might be bit confusing now, I will try to clean it up a bit.

Please start one thread per topic so others will keep up to date.

 

[koda2000]

The best way to measure the health of an engine is to do a compression test. If the compression is low or uneven, then the dealer's comment is correct. Otherwise if might be something relatively easy/inexpensive to fix. You're probably going to find that a lot of mechanics don't even want to mess with a 16+ year old 4.0L SOHC.

 

[Flash]

You're probably going to find that a lot of mechanics don't even want to mess with a 16+ year old 4.0L SOHC.

A lot of mechanics here weasel out of it by saying, "huh, Exploder" as if that meant anything.

 

[PAExplorerXLT]

You're probably going to find that a lot of mechanics don't even want to mess with a 16+ year old 4.0L SOHC.

That’s what I was thinking. Are dealers wiling to even take a 98 Explorer? It seems to me the kind of problems we are encountering here are way over their heads.