Engine miss above 2000 RPM

[Ecomike]

The base timing (timing chain and distributor are all fine, no changes made, or changes in the settings made or found in the inspection I did after the problem moved to 500 rpm. Same settings it has had for 12 years, and the same as they have been since I bought it 12 years ago). The distributor only has about 70,000 miles on it.

Tach is still normal, working fine and the Snap-On MT-2500 and my ear confirm they are all in sync on the Tach signal.

Yes, I tried clearing the Renix KAM memory once already. The STFT changed after that, but it did not fix the 2000-3000 rpm miss. I did that before it got worse, down to 500 rpm. Early on it was running rich and the STFT was compensating at idle. Now the STFT is all over the place, due to the miss fires at idle.

One thing that puzzles / concerns me is the wet oily film on the IAT sensor I cleaned yesterday when I pulled it, and the same on fouled spark plugs.

I wonder if the valve seals are shot after using Pen lube on them???? Oil fouling from shot valve seals???

But how did I oil get all over the IAT sensor. The EGR is working properly. Maybe backfires on decel???

hows the timing on it? have you ever changed the chain or removed the distributor? the only thing i can think of is its losing its crank signal. is the tach jumpy when its hesitating?

also STFT should be jumping quite a bit. LTFT wont really change until you drive it.

have you disconnected the battery during any of the diagnostics?

 

[Green Mesa XJ]

Never done one, not sure what it tell me that the compression test did not already tell me (data in older posts here)? I think I have enough compressed air to do one. But what would it tell me?

Leak down test would help indicate if the valves are leaking, or if there is a leak and where, like if it's a intake valve you'd hear it hissing through the intake, head gasket you'd could see or hear it bubbling.

Kind of a pain to do because you have to rotate each cylinder so the valves are closed but a good tool for indicating were a mechanical fault is.
Only helps If there is a mechanical issue beyond what you expect so might not be worth it unless everything else fails to find the issue.

I can't think of a good reason to have acceptable compression and this problem.





Sent from my iPhone using Tapatalk

 

[90xj06]

oily iac could be from the ccv. they always leak some in. hows your air filter? also try misting some water over the spark plug wires and look for blue arcs. i have seen spark plug wires look good but light up like a Christmas tree when wet.

is there excessive slack in the distributor shaft? sounds like the timing is out a bit. whats the mt-2500 showing for knock counts? might want to pull the plug on the sensor and see if that has any effect. i don't have mine hooked up. mainly because it got sheered off during the engine swap.

 

[Ecomike]

Thanks, I will try that.

My knock sensor is not connected. I do wonder if reconnecting it might help with this issue?

Air filter and CCV lines are all in good shape. I was thinking the oil came from the carb cleaner dissolving the carbon crud, and then maybe oil, pen lube I sprayed on the upper valve train and valve seals, plus blow back from the leaky valve seals made the intake worse that when I started. And now gas is washing it into the cyls and fouling the plugs. One reason I was thinking of using ether, starting fluid, it might help dryer her out?

oily iac could be from the ccv. they always leak some in. hows your air filter? also try misting some water over the spark plug wires and look for blue arcs. i have seen spark plug wires look good but light up like a Christmas tree when wet.

is there excessive slack in the distributor shaft? sounds like the timing is out a bit. whats the mt-2500 showing for knock counts? might want to pull the plug on the sensor and see if that has any effect. i don't have mine hooked up. mainly because it got sheered off during the engine swap.

 

[old_man]

It is not unusual to look inside the intake and find a coating of black oily buildup. Many vehicles have this issue, not just Cherokees. I pulled my throttle body last weekend and was surprised to find it all black and oily. It is caused by the overlap in valve timing (aka reversion). It had my IAC totally covered and I ended up taking carb cleaner and a toothbrush to it to clean it up.

When I did my valve job, I had the valve guides bored and sleeved with bronze, along with new valve seals, so they should be good.

 

[Ecomike]

Tap water might do that with even new plug wires?

oily iac could be from the ccv. they always leak some in. hows your air filter? also try misting some water over the spark plug wires and look for blue arcs. i have seen spark plug wires look good but light up like a Christmas tree when wet.

is there excessive slack in the distributor shaft? sounds like the timing is out a bit. whats the mt-2500 showing for knock counts? might want to pull the plug on the sensor and see if that has any effect. i don't have mine hooked up. mainly because it got sheered off during the engine swap.

 

[Ecomike]

Thanks Old_Man, That helps...

I have a good spare Renix head ready to go to the machine shop for cleaning, testing and prep as needed for use on this engine. Was just hoping to do it in the fall. But if this is a head valve problem, the over time clock has run out

It is not unusual to look inside the intake and find a coating of black oily buildup. Many vehicles have this issue, not just Cherokees. I pulled my throttle body last weekend and was surprised to find it all black and oily. It is caused by the overlap in valve timing (aka reversion). It had my IAC totally covered and I ended up taking carb cleaner and a toothbrush to it to clean it up.

When I did my valve job, I had the valve guides bored and sleeved with bronze, along with new valve seals, so they should be good.

 

[Runnin'OnEmpty]

Originally Posted by Ecomike
.......Still will run, but only runs, stumbling badly at 500 rpm and does not care if the throttle is at idle (actually need to open the throttle just a little bit or she dies after 10 seconds) or at WOT, which puzzles the hell out me. Its like its getting the same amount of fuel and air at idle as it does at WOT. It runs the same, same stumble at WOT as it does at idle.......

For this to occur, an engine has to be obstructed on either the intake
or exaust side. If the intake tube is free and open, then the exhaust
must be obstructed. The likely culprit is the catalytic converter. Even
though there is enough opening for the engine to idle, a restriction
is keeping it from increasing RPMs. An idleing engine still puts out a
lot of exhaust which may appear at the pipe end to be normal.

If the cat is bolted on, it's easy to check. If it's welded, you might have to remove the muffler to be able to shine a light into the cat
to check it...

 

[md21722]

What's interesting is attempting to clean the intake made the problem worse. I have a vacuum gauge with a fitting that threads into the O2 bung hole so the exhaust back pressure test is a 5 minute job with a beer in each hand. What was the compression test results? With 88 posts I don't really want to look to try to find it ;-) On my own Jeeps I've found valve work at 160,000 is not unreasonable and will boost compression. You could try more intake cleaner and see if it will even start. :gee: Basically what I'm saying is with 293,000 on the clock, pulling the head and taking it to a machine shop is not an unreasonable thing to do even if it doesn't solve your problem (which it may). The other thing you can do is pull the valve cover and manually whack the valve stems with a hammer. Sometimes that helps if they are sticking.

 

[Ecomike]

I back probed the Renix CPS and it is getting up to about 2 volts AC running in spite of the low rpms (300-500) and severe misses. It bounces from 1-2 volts. Still puts out .60 Volts cranking
--------------------

Or too many miss fires for it to ever be able increase RPMs? Its almost like it is firing on just 1 cylinder, maybe 2.

But I am starting to really suspect the Cat converter too, so I am inclined to agree. Had a Bad cat 2 out of 3 times in 40 years that acted a lot like this. One was this jeep when I bought it 12 years ago. I am afraid mine is welded, and in my driveway

May have to disconnect the exhaust pipe at the manifold flange to test it?

Problem is how to fix it in the drive way since I don't do welding

For this to occur, an engine has to be obstructed on either the intake
or exaust side. If the intake tube is free and open, then the exhaust
must be obstructed. The likely culprit is the catalytic converter. Even
though there is enough opening for the engine to idle, a restriction
is keeping it from increasing RPMs. An idleing engine still puts out a
lot of exhaust which may appear at the pipe end to be normal.

If the cat is bolted on, it's easy to check. If it's welded, you might have to remove the muffler to be able to shine a light into the cat
to check it...

My vacuum gauge showed it was OK, until it would miss at 3000 rpm, then during the miss fires it would drop to 10" of vacuum till it recovered, then back to 17". That is why I never seriously considered the Cat Converter. But now it can't get over 10" at all IIRC, at 300-500 where it barely runs. It dies at idle, need to hold the TB valve plate open some or it dies. Even at WOT it never gets over 500 rpm now.

Compression was 150 psi on 3,4,5, and 6, and 140 psi on Cyl 2 and 135 psi on cyl 1.

Cyl 1 and 2 have needed new valve guides for years and have spark plug oil fouling issues (been like that for 70,000 miles).

What's interesting is attempting to clean the intake made the problem worse. I have a vacuum gauge with a fitting that threads into the O2 bung hole so the exhaust back pressure test is a 5 minute job with a beer in each hand. What was the compression test results? With 88 posts I don't really want to look to try to find it ;-) On my own Jeeps I've found valve work at 160,000 is not unreasonable and will boost compression. You could try more intake cleaner and see if it will even start. :gee: Basically what I'm saying is with 293,000 on the clock, pulling the head and taking it to a machine shop is not an unreasonable thing to do even if it doesn't solve your problem (which it may). The other thing you can do is pull the valve cover and manually whack the valve stems with a hammer. Sometimes that helps if they are sticking.

LOL, I asked about using a hammer to wack the valve stems, many posts ago here, got no reply till now, LOL. Thanks

 

[cruiser54]

Didn't you already do this?

Cruiser’s Vacuum Test for Exhaust Restriction

Your vacuum gauge should come with an instruction booklet outlining this procedure.

Hook the vacuum gauge up to a source on the intake manifold.
Start the engine and note the vacuum reading.
It’s usually 17 to 21 inches of vacuum.

Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle.

Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading.

If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

 

[Ecomike]

Yes twice. It past the vacuum tests twice at up to 3000 rpm... before it totally crapped out...(1)

Have you read my posts? It will not go over (1) 500 rpm even at WOT now, and can not get over about 10" of vacuum due to the constant miss fires. Hard to pull a vacuum when it barely runs at all. If the vacuum was this low at idle with out all the puking and popping, I would be sure it was a blocked intake or exhaust.

Good info for future readers here though.

Didn't you already do this?

Cruiser’s Vacuum Test for Exhaust Restriction

Your vacuum gauge should come with an instruction booklet outlining this procedure.

Hook the vacuum gauge up to a source on the intake manifold.
Start the engine and note the vacuum reading.
It’s usually 17 to 21 inches of vacuum.

Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle.

Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading.

If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

 

[Ecomike]

Yes twice. It past the vacuum tests twice at up to 3000 rpm... before it totally crapped out...(1). At 3000 rpm it would miss fire badly, Vacuum would drop to about 10" at a steady miss firing RPM at 3000 rpm, and do what it is doing now at 500 rpm.

Have you read my posts? It will not go over (1) 500 rpm even at WOT now, and can not get over about 10" of vacuum at all now, due to the constant miss fires. Hard to pull a 17-20" vacuum when it barely runs at all. If the vacuum was this low at idle with out all the puking and popping, I would be sure it was a blocked intake or exhaust.

Good info for future readers here though.

Didn't you already do this?

Cruiser’s Vacuum Test for Exhaust Restriction

Your vacuum gauge should come with an instruction booklet outlining this procedure.

Hook the vacuum gauge up to a source on the intake manifold.
Start the engine and note the vacuum reading.
It’s usually 17 to 21 inches of vacuum.

Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle.

Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading.

If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

 

[cruiser54]

I wonder why it didn't show in the initial test.

 

[Ecomike]

I wonder why it didn't show in the initial test.

There may have been multiple moving targets. The Cat may have busted after I lubed up the valve train? I know the MAP sensor Vac line had to adding to the problem at first. Perhaps a back fire in the last moments after cleaning the intake took out the Cat, after I had fixed the MAP sensor Vac line. I am well known for tackling Medusa head problems, LOL. I never tackle simple problems, LOL. Just no challenge to it, LOL

The Vacuum gauge test has its limits. It is useless if the engine no longer runs, LOL. But seriously if it is the Cat, it is so blocked now that that test can not be run as written.

One test they do run at muffler shops is to test the pressure drop, differential across the Cat, by cutting a hole in the pipe just in front and behind the Cat. They say there should be no noticeable pressure drop. At some point, pulling the Cat, or swapping the engine head, changing parts may be left.

8Mud had a history of spark plug wires causing this kind of misfire that had too much resistance in the primary wire. I plan to try a new Cap, rotor and plug wires (and test mine with an ohm meter), and then try a new CPS if needed, before I try the exhaust hack saw method. The last thing will be the head if needed.

I was hoping to do the head job in cooler weather in Oct.

I do not think this is wiring, or the ECU.

I do like the idea of cutting of the fuel supply and starting it with a can of starter fluid or Carb cleaner in a spray can. That worked well on an 84 , jeep 4 banger I bought and fixed about 6 years ago.

 

[Runnin'OnEmpty]

If it will rev up on starter fluid, that narrows it down.....

As you mentioned, disconnecting the header pipe will quickly
tell if the cat is clogged....IF the studs/nuts aren't too rusted.

One other thing I can think of is to do an ohm test on the
coil to distributor wire. It will only take a minute. Spark to all
cylinders travels through that wire, and it's easily overlooked.
(4-8K ohms is normal for that particular wire)

 

[Ecomike]

If it will rev up on starter fluid, that narrows it down.....

I agree, it will tell me to maybe change the CPS, or look for a wiring problem to the Injectors!!!

As you mentioned, disconnecting the header pipe will quickly
tell if the cat is clogged....IF the studs/nuts aren't too rusted.

I had them off about 11 years ago when I swapped the AW4. They should be brass or copper nuts, something 5-90 taught me to do.

One other thing I can think of is to do an ohm test on the
coil to distributor wire. It will only take a minute. Spark to all
cylinders travels through that wire, and it's easily overlooked.
(4-8K ohms is normal for that particular wire)

I thought they were 1000 ohms per foot? That would make that primary wire about 1000 ohms?

I forgot to mention that right after the RPm problem moved from 3000 to 500 rpm, I found a busted ceramic spark plug insulator (one I cleaned the day before) and a second one that was loose. After fixing those and the MAP sensor vacuum line, and replacing the MAP sensor E-connector and CPS harness side connector it did not change anything, still barely running at 500 rpm, so something else went bad, or got worse during that time, just after I soaked the valves.

I still cant help but wonder if the 2 pen lube products and straight MMO I soaked the valve train with damaged the old valve seals to where they now let oil flood the intake???

 

[Hypoid]

I still cant help but wonder if the 2 pen lube products and straight MMO I soaked the valve train with damaged the old valve seals to where they now let oil flood the intake???

My money is on compression getting past the rings, AKA blowby. If you have not repeated the compression test since dumping solvent down your intake, I'd start there. I would also do the shade tree leakdown test.

 

[Ecomike]

My money is on compression getting past the rings, AKA blowby. If you have not repeated the compression test since dumping solvent down your intake, I'd start there. I would also do the shade tree leakdown test.

Compression was tested just after dumping as you put it "solvent" down the intake.

I ran the 12 0z can carb cleaner aerosol spray into two intake holes and the throttle body while running the engine. Then with the valve cover off, I sprayed 2 different pen lube products, PB Blaster was one, and the I sprayed MMO all over the valve train, and on top of the lifters.

It ran the same right after doing all that, that night, could still work my way up to 3000 rpm slowly before the miss got bad, rapid acceleration would still cause a miss at lower rpms. I also found the MAP sensor vac line hidden rubber hose, short piece gone bad. fixed the MAP hose....etc issues the next morning, then fired here up and for a week now have not been able to get her over 500 rpm. After that I reran compression test, all were still the same. Cyl 3,4,5,6 all 150 psi. Cyl 1 still 135 psi, and cyl 2 at 140 Psi. Same as the last 12 years.

Since then spark plugs have been cleaned, replaced, spark tested, MAP sensor and CPS tested, MAP and CPS connectors cleaned and replaced as needed, fuel injector rail had already been pulled and injectors tested with a 9 volt battery, all tested good, connectors cleaned first.

 

[Ecomike]

My money is on compression getting past the rings, AKA blowby. If you have not repeated the compression test since dumping solvent down your intake, I'd start there. I would also do the shade tree leakdown test.

If the Cat is blocked I am not sure a leak down test would be valid???? With the compression unchanged why would I do a leak down test?