Running Lean

I've got a 87' XJ, 4.0 with a manual tranny. As some of you may remember I posted up a few months ago when I had major engine carnage, we'll my engine is back in the shop, again...my problem seems to be that I keep scoring up the sides of my pistons. From what I understand its A: Over heated, which I'm sure I can rule that out, B: Running lean or C: Pistons too tight.

Originally the engine was .020 over with all new pistons, bearings, etc...major failure happened at 25,000 miles. Rebuilt 3 months ago with all new bearings and one new piston, cylinder 1. The first night I thought I heard a VERY mild valve train noise, drove it a week and one morning it was fine, drove an hour and it was knocking. Now cylinder 5 piston is bad and all other pistons are getting scored already. Not sure what to think, the Jeep runs fine, passes smog and everything else seems to be up to par as far as engine management. I've smoke checked the engine, checked EGR and a few other things and from what I could tell I never thought it was running lean. My engine is absolutely stock BUT, I am running a totally stock 95 HO long block with all my RENIX smog equipment. Has anyone ever had this problem or know of any ideas. I just want to frick'n use my Jeep damn it.:hang:

Here is my old post, the entire post is in regards to what had happened at 25k after my rebuild OR about 3 months ago. Note the picture with piston scoring.

http://naxja.org/forum/showthread.php?t=1046088&page=3

So has anyone ever encountered this issue with the piston scoring and an extreme running lean condition? I should have asked my question clearly but I guess I kind of made it a statement as to what happened more then anything. If anyone has had this issue or input I would like to know of possible causes for the lean condition. The thing is, my Jeep passed smog perfectly fine and other then ruining the pistons I haven't had any drive ability issues, detonation, miss fires, I've checked for vacuum leaks. Not sure where to go, ANY IDEAS? Maybe in range sensor failure?

Sounds like there wasn't the proper piston to cylinder wall clearance. Lean would wanna melt the piston tops.

Didn't read the other posts but scoring of the cylinder walls can be caused by a leaky injector. When you stop, it floods the cylinder with gas and washes off the oil. Have an analysis of your oil done, or the old school method is to simply smell the oil and see if it smells like gas.

cruiser54 said:

Sounds like there wasn't the proper piston to cylinder wall clearance. Lean would wanna melt the piston tops.

Click to expand...

That's what I suspected but upon some calls to local shops and some internet research it could be lean too. I'm just stumped as to why it could be running so lean with no noticeable drive ability problems. You'd think if its bad enough to score up the pistons it show other symptoms. I wonder if a MAP or O2 sensor can cause this? If it happened to all 6 pistons logic would say its a computer or fuel injection problem VS a vacuum leak or something of the sort...could have a bad C101 caused this?

Have you looked at the oil. It is far more likely that an injector is leaky because if it were running lean enough to score the walls, you would have melted a piston as well and would not have passed emissions.

old_man said:

Have you looked at the oil. It is far more likely that an injector is leaky because if it were running lean enough to score the walls, you would have melted a piston as well and would not have passed emissions.

Click to expand...

Yeah, right now piston 5 is bad but all other ones are starting to go. I'm thinking is has to do with how much pulse width the computer is giving the injectors and/or a faulty sensor causing this issue.

I've read and talked to a few mechanics that said the top of the piston wont always get burned but when it runs lean sometimes the piston gets hot and expands, gets soft and scores up or starts to transfer metal. Mine look just like that. It just sucks because once I get the engine back in I need to start figuring out why this is happening.

Does anyone know what the normal injector pulse width is for a RENIX ecu and does anyone know the max it will deliver?

What sensors and connections are common for fuel strategy?

TPS, O2, ECT? MAP? stuff like that...any ignition faults?:anon:

I have not checked the oil btw, I still have it in a container in my garage. I'll have to give it the sniff test just to see.

---Just thoughts---

-How is the oil system ? Any signs of weak flow at low or high rpm? Clogged passages. Flaky oil pump relief valve/ filter?
-Good long Break-In period?
-Brand oil/filter and type, weight, etc.? Break-in oil????
-------
Be tempting to replace the 'puter and sensors (Salvage)
and fuel injectors.

Wonder if a shop with dyno testing could check fuel/air ratio during start-warmup-operating temperature/ Cost???

Might get some oil sample kits and test oil at 100 and 500 miles and at first few changes.

GOOD LUCK,
Orange

May also want to look at broken or loose fitting piston rings.

Just curious if you had a vacuum leak, what was your idle speed? I know I mentioned this before, but you should raise the renix intake a little higher on the HO head. Because the ports do not match right if you just bolt it right on. There is a small section on top of the intake runner that looks like it mates to the head but it actually is not contacting the head at all. If you have the old intake gasket and lay it on the head you will see the imprint on what i'm talking about. I spent much time making this work for my application when I did the stroker. I hope you figure this out, because that really sucks.

Things that directly affect fuel mix on the renix:
O2 sensor
MAP
TPS
FPR

pretty much everything else is there for ignition.

If it runs well I would suspect a fuel pressure or regulator problem before I suspected that the fuel trim on the ECU is all out of whack. Check that the O2 heating element circuit is working. iirc it's run from the ASD relay, but it's been a while since I looked at it.

I would also check for:
intake leaks
exhaust gasket leaks

Ideally I think you should fine a shop with a dyno, fuel pressure gauges and the wideband O2 monitoring stuff that goes along with it. That way you can know if it's an oiling problem, leaky injectors, or a lean condition while running. Spending $100 at the dyno shop will save you tons of troubleshooting headaches.

IH392 said:

Just curious if you had a vacuum leak, what was your idle speed? I know I mentioned this before, but you should raise the renix intake a little higher on the HO head. Because the ports do not match right if you just bolt it right on. There is a small section on top of the intake runner that looks like it mates to the head but it actually is not contacting the head at all. If you have the old intake gasket and lay it on the head you will see the imprint on what i'm talking about. I spent much time making this work for my application when I did the stroker. I hope you figure this out, because that really sucks.

Click to expand...

Your a 100 percent correct, I pulled it apart at work today and found exactly what your talking about. This may or may not be my entire problem but this is a damn good start, thanks. As for moving it up, how far did you move it and did you re drill the holes, elongate them with a round file or just remove the dowels from the head. I'd like to be able to some what use the dowels still. Also, are the RENIX and HO manifold gaskets the same or no?

Any other information will be awesome also, thanks again!

Use the Renix intake/exhaust gasket. You don't have to elongate the holes for the dowels. You MAY have to file the rear most part of the intake manifold to get it to clear the rear header tube and fit snugly to the head.

87manche said:

Things that directly affect fuel mix on the renix:
O2 sensor
MAP
TPS
FPR

pretty much everything else is there for ignition.

If it runs well I would suspect a fuel pressure or regulator problem before I suspected that the fuel trim on the ECU is all out of whack. Check that the O2 heating element circuit is working. iirc it's run from the ASD relay, but it's been a while since I looked at it.

I would also check for:
intake leaks
exhaust gasket leaks

Ideally I think you should fine a shop with a dyno, fuel pressure gauges and the wideband O2 monitoring stuff that goes along with it. That way you can know if it's an oiling problem, leaky injectors, or a lean condition while running. Spending $100 at the dyno shop will save you tons of troubleshooting headaches.

Click to expand...

I've got a lot of diagnostic tools like scanners and graphing multimeters along with a ton of other crap but no dyno. I was thinking if I bought a wide band A/F gauge and while driving kept an eye on things. I can always tap into different circuits and sensors, keep an eye on scan data and watch the A/F gauge.

Its gotta be something effecting the entire system if its ruining all pistons. Maybe a dyno is the way to go because it can load the engine and test emissions at the same time.

cruiser54 said:

Use the Renix intake/exhaust gasket. You don't have to elongate the holes for the dowels. You MAY have to file the rear most part of the intake manifold to get it to clear the rear header tube and fit snugly to the head.

Click to expand...

Wait if I don't elongate the dowel holes then did you completely remove them?

A spur of the moment kind of thought would be maybe picking up a HO intake and running that until I have to smog the vehicle. BUT not running EGR on a EGR system might have negative side effects also.

I don't know how a different gasket would change anything, when there is section on the runner that doesn't even mate to the head. I raised the intake about an 1/8th of an inch. I elongated my holes with a die grinder using a cutting burr, or a dremel would work. The only problem you'll get is that it will expose a nasty ridge from the head's intake port and probably hurt the air flow. I ground that down when I worked on the head. Sometimes I wonder if would have been better off with the renix head, and just ported and polished everything and called it good. If you could use the HO intake that would be better, blocking off the EGR won't hurt anything, but that would be a pain to have to convert back everytime you smog though.

IH392 said:

I don't know how a different gasket would change anything, when there is section on the runner that doesn't even mate to the head. I raised the intake about an 1/8th of an inch. I elongated my holes with a die grinder using a cutting burr, or a dremel would work. The only problem you'll get is that it will expose a nasty ridge from the head's intake port and probably hurt the air flow. I ground that down when I worked on the head. Sometimes I wonder if would have been better off with the renix head, and just ported and polished everything and called it good. If you could use the HO intake that would be better, blocking off the EGR won't hurt anything, but that would be a pain to have to convert back everytime you smog though.

Click to expand...

Mine works just fine using the Renix gasket. I did match port both the intake and the head for better flow, but that didn't affect the sealing.

The HO gasket doesn't have enough material on it and causes the leak when installing a Renix intake on an HO head.

As for airflow, these aren't Indy cars. And compared to most OEM tolerances, if you've ever looked at some stock ports, this slight mismatch isn't any worse than what Detroit put out for years .

IH392 said:

I don't know how a different gasket would change anything, when there is section on the runner that doesn't even mate to the head. I raised the intake about an 1/8th of an inch. I elongated my holes with a die grinder using a cutting burr, or a dremel would work. The only problem you'll get is that it will expose a nasty ridge from the head's intake port and probably hurt the air flow. I ground that down when I worked on the head. Sometimes I wonder if would have been better off with the renix head, and just ported and polished everything and called it good. If you could use the HO intake that would be better, blocking off the EGR won't hurt anything, but that would be a pain to have to convert back everytime you smog though.

Click to expand...

I noticed the edge too, seems like a lot of hassel. I wonder if I should just pick up a RENIX head and have that looked over and re done. Its not like my Jeep is going to be a power house of raw horse power. Is the RENIX head really that crappy for power? Mainly I want reliability.