• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Rough Idle - p171

wacky

NAXJA Forum User
Location
Colorado
Here's the story.
Brother in-law inherited a 99 xj from his dad.
Dad had driven the jeep for 40 miles with the check engine light on. Then had it towed to the dealership the next day.
It was taken into the stealership. They diagnosed blown head gasket, cracked intake manifold, and low fuel pressure. 30psi when 49 was supposed to be stock. Dealership replaced fuel pump.

I towed XJ to my house and diagnosis began. Head gasket confirmed as shot with bubbling exhaust through overflow tank. I tore it down and confirmed a shot head gasket. We replaced gasket and had head machined flat (.019) then it was magnafluxed for leaks. No cracks were found on the head.
I replaced the cracked intake manifold
We reassembled the engine and flushed radiator and block, changed the oil. topped off all fluids.

Jepp started up fine (whew!). Temps stabilzed to the 210 range that my own 99 sits at.

We immediatley noticed a rough idle.....then upon test-driving noticed some hesitation off the line. But otherwise driving fine at speeds between 25-55...but rough idle still doesn't seem right......BAM...check engine light illuminates. We headed to Auto Zone and they pulled a p171 code: "lean on 1st bank."

I did some reading here tonight. NAXJA posts indicated things such as vacuum leaks, MAP sensor, O2 sensor.
I swapped the original MAP sensor from the original intake manifold to see if that would clear up the rough idle. No dice. Then, suspecting I'd nicked a vacuum line I ran some propane around all the vacuum lines in an effort to diagnose a vacuum leak. No change in the rough idle occurred.

At this point I'm kind of stumped.....and quite tired.

O2 sensor? Is there a way to check this without just swapping in a $60 new one?

Any other ideas?
Could this lean condition have led to the blown head gasket? If i remember correctly, lean=hot...thus the head gasket.
Thoughts?
Tips?
 
I take it the Machine shop verified the valves in the warped head were all good????

I would do a leak down test on each cylinder on the lean bank to see if there is a valve leak.

Yes, you can test the O2 sensor output. Test method is posted in many threads here (by me). Use an analog volt meter, look for 0-1 volt output, should be reading 0.45 and should bounce back and forth across the 0.45 reading except at WOT, rapid acceleration or rapid decel. Since you have a lean computer code, not much sense in testing the installed O2 sensor at say idle right now (as it probably is reading lean, but testing both would tell you which bank is running is lean!!!) , but you could test it at rapid acceleration and deceleration to see if it goes from 0 to 1 volt like a good O2 sensor should!!!!! Note you have (4) O2 sensors. You need to determine which one(s) to test. Probably one of the 2 pre cat sensors.

An intake manifold leak (crack) is odd I think??? Wonder why the last one cracked?

Yes, lean means too hot, and can blow the head gasket and burn exhaust valves up.

Could be a bad O2 sensor, but it could be an exhaust manifold leak upstream of the O2 sensor fooling the O2 sensor.

Not to hijack this thread, but I am doing a head gasket right now (my first) and wondering if the top of the block ever warps when and if the head warps??? IF, yes what do you do?
 
I didn't get the valves checked. They passed my visual inspection....i.e. not roasted and no holes in them.

This a.m. we did a cap/plugs/rotor/wires. That smoothed up the idle some.
We cleaned the idle control valve.....
We replaced the upstream 02 sensor, because after a visual comparison with the one from my 99 XJ it was obviously either: A-really dirty or B-burned up
The o2 sensor on my own 99 was light tan and seemed to be in fine shape.

The old intake crack was at the very rear boss/bolt hole. No idea why it cracked....it was cracked before we pulled it out so it wasn't 'user error'.

It drives excellently from anything above idle to 80mph. We took it on an extensive test drive this a.m. after the above issues were addressed. I had cleared the 'check engine' light this morning, and it so far hasn't reappeared (fingers crossed).

It's idling at about 750-850, while my manual jeep consistently idles right at about 1000. Do Automatics idle lower??

I can't answer your question about a warped block, but common sense tells me you'd need to pull the engine and get it decked.
 
700 to 750 rpm is spec idle speed in park. Mine runs at 700 rpm in park (AW4), 500 rpm in drive at at idle, and 700 rpm in drive with the AC on. Mine is an 87 Renix.

Just dawned on me that a partially plugged fuel injector could cause a lean condition and rough idle, but I would think it would cause a rough running engine at any rpm. Might pull the injector wires one at a time to see if any one of them is not contributing power at idle. When you pull and injector wire set it should make the engine run rougher, noticably. Alternatively you could just pull the spark plug wires one at time. Does the same test.

What spark plugs are you using?
 
this afternoon got a P0302 code- misfire in cylinder #2

thoughts?
'Zone said
1.vacum
2. fuel pressure
3.plugs/cap/wires
4. injectors

It has new cap/wires/rotor/plugs, new fuel pump, I've checked for vacuum leaks....
how do I test injectors?
 
PO302 can be caused by a leaking valve, probably exhaust valve, low compression on cylinder #2.

Sorry to post the bad news. Since you already did the head gasket, and did not service the valves, I would suspect a valve on cylinder #2 is bad.

or no fuel, or too little fuel in cylinder #2 can throw that code. A compression test on #2 would answer the question of which it is.

Scratch vacuum, and fuel pressure, those would affect all the cylinders. Bad plugs, wires on #2 would make it rich, not lean. Since you had a lean ssue before, I am leaning towards burned valve or bad fuel injector. Bad valve is at the top of the list.

wacky said:
this afternoon got a P0302 code- misfire in cylinder #2

thoughts?
'Zone said
1.vacum
2. fuel pressure
3.plugs/cap/wires
4. injectors

It has new cap/wires/rotor/plugs, new fuel pump, I've checked for vacuum leaks....
how do I test injectors?
 
By shaving the head .019", you have decreased your head cc from 58cc to 55cc(or 57 to 54), thus raised compression from 8.76:1 to 9.04:1 (or 9.14:1). You might need to run a higher octane gas now, but I'm not sure why it would need more gas to richen up the mixture.
 
wacky said:
Would a basic compression test tell answer this or should I do a leakdown test?

Compression test will tell you if there is a leak, leak down test can tell you where the leak is.


One other long shot (Not sure about this at all) is a bad o'ring seal on the fuel injector for that cylinder. It can cause vapor lock on an injector (read in recent threads here), and draw in excess air (leaning out the A/F) but I would think the ECU would compensate with more fuel on that cylinder, which would cause other problems and symptoms.

Leak down test will tell you the most the fastest.
 
update:
I took it to the local mechanic for a more thorough diagnosis. I had him double check the fuel pressure. It checked out good.

compression / leakdown tests are not good.
cyl 1-90
cyl 2-65
cyl 3-45

my mechanic seems to believe that the rings got roasted when it overheated initially, but they regain their springiness once the engine gets up to speed. Should I have been able to check for the bad rings when it also had a blown head gasket? I wouldn't think so, as it wouldn't have held compression either way....

He's saying either valves or rings, but because of the massive blowby he's leaning towards rings. He also seemed to indicate my machine shop would have checked the valves when I had it in for decking/crack checking....just as a matter of standard business practice. I'll call them later today to see if this is something they regularly do.



At this point I'm going to try a dose of snake oil mixes and then see what happens.

looking to the future:

At this point my bro-in-law has about $600 into this xj. What do you guys think he could sell it for in its current condition?
127k
immaculate interior
crappy engine...grrr
nice/excellent exterior
 
If he did the leak down test properly, he should have been able to tell you which valves, if any were leaking (not sealing) as they would blow air out the tail pipe. Machine shops only do what you ask for and pay for. Small leaks in valves can go undected with just a visual inspection. So don't write off the valves as a problem just yet.

Did you follow the FSM procedures, bolt tightening sequence, and bolt torque specs using a torque wrench when you installed the head?

Did you use new head bolts??? If you used the old head bolts were they painted? If yes, they were already too used up for reuse!!!! Head bolts on Jeeps can only be used twice. They should be painted when they are reused so they do not get used a third time. If you did not follow the FSM tightening sequence, and torque specs, the head may be warped again.

Some people just go and get a lower mileage engine out of a junk yard for under $200, drop in and go.

In your case, if it is the rings (and it sounds like he saw enough blow by on just those three cylinders to claim its the rings, right???) there are some rare possibilites such as crude on the rings, or lined up gaps in the rings that can look like a permanent ring problem.

IF you are sure you did the head gasket properly, and that it is not the valves, then here is what I would do. Buy a can of seafoam, quart of Marvel mystery oil, quart of Mobil 1 10W30, and the rest 20W50 dyno oil. Drop that in there with a new oil filter and run it for about 1 hour, and run it up and down in rpm up to about 4000 rpm and back to idle. Watch the oil pressure closely. Then check the compression again if you have a comp tester. Then run the piss out of it on the freeway for about 10 miles, at about 3000 rpm. This will help clean up the rings (if they are foulded any with sludge and carbon), and lossen them and help them seal better.

Then I would drain the oil, change the filter (don't use Fram), and use one can of Restore, a quart of Lucas oil additive, and 20W50 dyno oil, run it for an hour, test the compression again, then drive for about 500 miles and retest the compression again. Restore takes a while to work, the other higher viscosity stuff should help some right away.

Restore has coloidal soft metal (nano particles small enough to stay in suspension and to pass through the oil filter)made of copper silver and lead that plates out on the cylnder walls and rings and restores (thus the name) some of the lost compression.
 
Did you follow the FSM procedures, bolt tightening sequence, and bolt torque specs using a torque wrench when you installed the head?

yes, yes and yes

Did you use new head bolts???

yes
 
You could have visually inspected the cylinder walls for scoring, and measured run out on the cylinder walls with an ID caliper (?) gauge. A leak down test might have indicated a possible ring cylinder problem, but I doubt it would have been conclusive. Depends on where the head gasket fails.

So did this engine get coolant in the oil and run that way at all? IF so how long did it run with coolant in the oil? If so you might have bearing problems now as well.

If the bearings are also damaged, most junk yards sell complete used engines from wrecked vehicles for under $200 with a warranty! You can check the odometer, and crankase oil and valve cover area ahead of time in most cases to make sure you get a good engine. I would try the snake oil I listed below first, if that does not solve the problem (but it might, so try it first), I would hit the junk yard for an engine. Or post up here to see if there is one for sale in your area on NAXJA.

wacky said:
Should I have been able to check for the bad rings when it also had a blown head gasket?
 
Guess we can scratch this concern, LOL.:D

gradon said:
By shaving the head .019", you have decreased your head cc from 58cc to 55cc(or 57 to 54), thus raised compression from 8.76:1 to 9.04:1 (or 9.14:1). You might need to run a higher octane gas now, but I'm not sure why it would need more gas to richen up the mixture.
 
air into cyl 2 comes out cyl 3....:-(

I don't feel like doing the junkyard engine swap. What's the going rate for a clean xj w/crappy engine??
 
wacky said:
air into cyl 2 comes out cyl 3....:-(

I don't feel like doing the junkyard engine swap. What's the going rate for a clean xj w/crappy engine??

That sounds like the new head gasket between cyl #2 and #3 is blown already!

I am doing a head gasket right now on one that burned out between #4 and #5.

I noticed that the new Felpro gaskets don't have as much metal reinforcement between #2 & 3, and between #4 & 5, but not sure why, They have more metal in the gasket between 1 & 2, 3 & 4, and 5 & 6.

Interesting that our failed gaskets are between 2 & 3 and 4 & 5! But I don't know who's head gasket was in this one before I got it. Could have been OEM.

Value depends on local market, year, and condition.

By the way, runnning too lean can burn parts up like exhaust valves and head gaskets.

I paid $900 (top dollar) for an 89 XJ, 114,000 miles, that I knew probably had a bad head gasket (took a chance it was other cheaper easier to fix items). It was, is in excellent condition on the inside. I think it was parked indoors or in covered parking, for 10 to 15 years. I paid $350 for a nice 87, partly stripped under the hood (no tranny, no AC, no radiato) and the engine had a rod exit the block, so the engine is scap metal. Bought it to part it out (nice interior, nice rims, good tires, etc) and scrap metal the rest.

I would guess you would be lucky to get $1000 even being a 99 (its already 9 years old), and should be able to get at least 500 to 600 for it, minimum.

Other than listeding it here, I would also list it on Craigs.org Sold my 73 LTD last year on there in just a few weeks, and it needed a new trunk, badly.
 
Back
Top