Help diagnose this emissions related problem (long)

Ok, I've been trying to get my rig to pass Colorado emissions since last November and I'm getting nowhere fast. It's high on all readings - Hc, Co, and NoX. Basically, it's running hot and rich.

Subject vehicle stats: '93 H0 with 5 sp (133K miles), non A/C, 4:56's, 35" tires.

Driveability is fine - runs good at high rpm's and has only a hint of a misfire at idle. No check engine light.

Terrible strong rich smell from the exhaust at all times. No visible smoke, no black bursts on acceleration. Good throttle response.

Replaced:
O2 sensor, MAP sensor, TPS, Coolant temp sensors (both), spark plugs, Oil pressure sensor, antifreeze, oil, thermostat, fresh tank of gas.

Recently replaced:
radiator (checked for calcium deposits and restrictions in fins just today) and I've had an aux. A/C fan hooked up and working for a year now.

Symptoms:
operating temperature with highway driving never lower than 220, under load goes into the red and boils. Trail use - I can keep it at 220, no boiling. Rich exhaust smell, slight misfire at idle, some backfiring on decelleration between shifts. Paper over the tailpipe test does show some occasional suction at idle.

Shadetree diagnostics done to this point:
-I've replaced the above sensors and parts which got it to just squeek by on Hc and Co, but NoX is still high.
-Using a strobe timing light with plug wire pickup, I see an inconsistant flashing of the light indicating a misfire condition to cyls 3,4,&5. Cyls 1, 2 & 6 are good.
-Plugs were pulled, look very clean, no unusual residues, smell like unburned fuel.
-Wires ohm checked and are fine.
-Compression test shows all cylinders in good shape: #1=120lbs, #2=125lbs, #3=125lbs, #4=125lbs, #5=125lbs, #6=120lbs.
-Cat converter appears fine as far as flow, but is OEM unit.
-I can't check actual timing since I don't have a magnetic pickup timing tool. I can't locate a notch on the balancer and the timing scale on the timing cover only has dashes on it - no numbers.
-I've replaced the fan clutch and discovered the old one was just fine.
-I've inspected the cap and rotor for cracks and loose contacts, and cleaned the contacts.

There you have it. I am at my wits end with this problem. I must be missing something. I don't suspect a head gasket problem since it doesn't use any coolant, and the coolant is clean, no oil or bubbling.

My only thoughts at this point are possible a low-functioning water pump and a wornout cat converter.

Would a bad water pump and bad cat be able to peg the emissions readings?

Another thing, emissions testing out here uses a dyno-based system where the vehicle is tested under "real time operation". The safety requirements for the dyno equipment limit tire size to 34". When I went for my tests, I borrowed a pair of 33" tires. I imagine this certainly raised my RPM's a bit at 60mph - which is the speed they take them to. I'm gonna try to find some 34's for the next attempt to help keep engine speed down.
They also have a large electric fan that they place at the front of the car during the test, I had the tech put the fan right under the bumper and aim it up to get max flow - but this didn't keep the engine from boiling over.

Thanks in advance fellas!

Bad water pump could cause a lot of your overheating isues; how old is it? I don't think that would cause high readings on the rest, but dude..you've got issues! How old is the lower radiator hose? Is it collapsing under suction? Am I thinking of something else, but aren't there two O2 sensors on that 4.0L? One at the manifold and one on the cat?

The way I see it, the overheating when driving on the highway can only be caused by three things; insufficient airflow through the radiator (something blocking its path e.g. winch), insufficient coolant flow through radiator (blocked radiator, water pump going bad, lower radiator hose collapsing, cooling passages in engine blocked), a bad radiator cap, or too much heat from the engine itself (lean condition, retarded timing). The only items that seem possible in this case are a collapsing lower radiator hose, blocked passages, or a bad radiator cap. I suggest you give the whole cooling system a good flush and replace the lower radiator hose and radiator cap as your first lines of attack.
You've replaced a lot of sensors and your engine's still running rich. I suggest you hook up a vacuum gauge to the intake manifold and measure the vacuum at idle, 1500rpm, and 2500rpm. It should be at least 16"Hg. If it's less than that, check for vacuum leaks. Another possibility is that your cat is going south. That could cause a rich condition AND high NOx emissions. You said you replaced the O2 sensor. Since there are two, which one did you replace? The one before the cat is the more critical one of the two and if that's the old one, it could be the cause of your rich condition.

Thanks for the quick replies guys.

I can rule out the lower rad. hose - replaced that in October before Moab along with the upper one. The lower has the steel spring inside to prevent collapsing. Radiator cap is new too.

Anyone have any experience with radiator construction? I seem to recall hearing a discussion about painting radiators being a bad idea. When I had my XJ painted, the idiot sprayed the front header and radiator support and didn't mask off the radiator. When I put it back together, I hit it with rattle-can black. So, I guess there's 2 layers of paint on the front of it now..... Can this keep the radiator from cooling properly? I've got a spare radiator from a '94 I parted out - maybe I should just swap that one in.... Or maybe I should just pony-up and get one of those 3-core radiators....

The water pump is OEM as far as I can tell. Gawd I don't wanna do that swap... Guess I'll have to. Who's idea was it to attach EVERY accessory bracket to the water pump anyway?

I'm discovering that the '93 XJ is kind of a wierd bird. A handfull of things were done differently than the previous years and the years after it. For instance, it only has one O2 sensor located just after the header on the exhaust pipe.

I'll look into the vacuum readings and do a spray test of the intake manifold at the gaskets. That just may be the cause of the stumbling / missing symptom at idle.

I'm also hearin' ya about the cat - it's 9 lives might be used up. Anyone know a good source for a replacement cat converter?

Thanks!

Several layers of paint on any heat exchanger (such as a radiator, or an a/c condenser) acts as insulation. That could certainly be part of your problem.

Having the big fan placed under your bumper certainly didn't help. The automotive cooling systems are designed to shed heat through the radiator, not directly off the block. You would have done better to let them put it where they usually do, in front of the vehicle so it blows on the radiator.

You might also have your radiator flow tested at a rad shop. IMHO ten years is all a stock radiator is good for. The one in my '88 actually sprung a leak at that point, but I had experienced sporadic overheating in extremely hot weather for the two summers prior to that. Cores were about 75% clogged with mineral deposits. In the new radiator, I use only distilled water. Tap water around here has a high mineral content.

One other point -- has your speedo been regeared to correct for the big tires? If not, the vehicles computer sees you driving at 40 or 45 when the tires (and the test dyno) see 60. This can cause all sorts of confusion. There are more ramifications to not correcting the speedo gear than just the possibility of a speeding ticket (which, of course, is a non-issue for you).

I have a 92 and it only has one O2 sensor. I believe the dual O2 sensor started in 96.

Two coats of paint really shouldn't be a problem unless they are really thick. Swapping the radiator does sound like a good idea. When you do that, put in a new water pump. Once you have done it, it s not so bad.

I was wondering if there might be a problem with injectors. Measure the resistance of each.

I would suggest replacing the plugs with Champ truck plugs. If you are running the high priced aftermarket plugs, the NOx will be higher. Do a search for more info on this topic.

I'd certainly check out the cat next.

Have you verified the T-stat is working properly? If in doubt, replace it with an OEM one. By the way, water pump R&R is fairly easy, so don't worry about trying that. I bought a lifetime warrantied pump from Autozone for cheap. It didn't fix my problem, so now I have a spare. It's all good. If everything suggested in the replies doesn't help, the only other things I can think of checking are the distributor and the computer.

Beware of some 3-row rads as the passages can be on the small side. The 2-row Modines seem to work well for many of us.

Lastly, and don't take it the wrong way as it happens to the best of 'em, but check that the spark plug wires are connected in the correct order. Good luck Troy....let us know if you find the culprit.

Tom

Eagle:

LOL - You musta misunderstood the placement of the fan at the emissions center. I didn't have 'em aim it at the engine, I just had them angle it up toward the radiator rather than being placed 15 feet in front of the XJ where the winch bumper was deflecting most of the air. My XJ sits way above most normal vehicle's radiator heights and the fan there isn't adjustible other that angles up and down, if the fan could be brought up higher and aimed directly into the grille, I think that'd work even better.

And yes, my speedo is corrected - to 35" tires. I think one problem I've identified just with some of the replies has got to be the fact that I borrowed 33" tires for the test - the engine had to work a bit harder (higher rpm's) to get the 33's up to 60 mph.

I have a hard time believing that my radiator would be flow restricted already, but anything's possible. When I replaced the t-stat, I looked into the water-jacket in the head and was fairly surprised at how clean it was in there. But maybe the high engine temps have boiled out the block and now my radiator is acting like a crud filter..... Taking it to a rad. shop and having it looked at might be a better idea than swapping in the OEM spare that I've got in the attic.

Thanks!

Anyone know anything about an "manifold air temp sensor" and if that could be contributing? Does it have anything to do with the amount of fuel being delivered?

YELLAHEEP said:

Anyone know anything about an "manifold air temp sensor" and if that could be contributing? Does it have anything to do with the amount of fuel being delivered?

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I've been told it does, but I can't verify that right now.........got to find my FSM pages. Hopefully someone can verify soon.

Tom

Joey, did you have a chance to measure the vacuum? I can loan you a guage if you don't have one. Also check the fuel rail pressure. Don't have one of those.

Your statement about what appears to be a miss on various cylinders leads me to think you may have a ignition problem. There are only a few things in the ignition circuit. They are the CPS, the ECU, the camshaft sensor, the ignition module/coil. See if anyone has a loner ECU and coil you can try. An erratic miss can be caused by a CPS that is either misadjusted or going bad. Are you using the stock mounting bolts on the CPS? Don't laugh, but they help to complete the magnetic circuit for the CPS and if you replace them with a different size or material, you can get screwy results. I would also put the engine at TDC and check the location of the rotor in relationship to the distributor cap. Being off by a tooth can give you lots of fits.

Old Man,

What's with this "Joey" stuff! You know better than that! Joey is the other Secretary/Treasurer that actually 'wheels his junk..... I'm the web-wheeler! :twak:

Anyway, thanks for your input. I've got a vacuum gauge (thanks for the offer) and I'll be looking at that issue this weekend.

I'm certain that my rig's problems are being caused by parts that have gone bad and not because of things not being installed properly. These problems have surfaced just this past year - my last emissions test was fairly clean and I haven't done any major work/repairs to the engine prior to these new problems. In other words, I'm sure the distributor isn't off a tooth and I'm certain the bolts on the CPS are still the factory ones. But, I haven't ruled out the CPS just yet - the symptoms just aren't typical of a bad CPS.

I'm also doubting that the coil is bad since the misfire is exclusive to cyls #3,4 &5 - I'd think that if the coil had issues, the misfire would be seen at all cylinders.

I'm also kicking around the idea that maybe I've got a bad head gasket or a crack in the head somewhere. The misfire is usually more noticable when the engine is cold - but not obviously so. Another suspicious fact is that the 3 cyls with the misfire are neighbors - I could see a warped head or water jacket crack causing this problem. I'm gonna borrow a leak-down tester from a friend and pressurize the cyls to see what that reveals. Maybe I'll see some bubbles in the coolant and be able to put and end to this mystery......

If the cyls test ok, then I'm gonna tear into the cooling system. If that doesn't reveal a problem, I may just swap in this '94 H.O. engine with 30K on it that I've been saving.... was hoping I wouldn't have to use it until my current engine blew up.

I'm still curious about the manifold air temp sensor though....

UPDATE:

Well, I pulled the drain plug outta the radiator and it poured for only a coupla seconds, then only a little trickle. Took off the heater hose from the t-stat housing, the upper rad. hose - still no more flow. I guess the pass. side of the radiator is pretty plugged up. I'll be taking the radiator in for repair today, hopefully this will be the fix I've been looking for. I've removed the old water pump as well since I'm into it this far & get a new one on there.

Still haven't figured out the misfire situation. Guess we'll see how it runs with the clean radiator in and hope it helps.

Thanks for all the help guys!

If all else fails you could always buy a conversion kit to run on propane where the only emission is carbon dioxide.

How are the spark plug wires? A failing wire will cause a miss.

Eagle said:

How are the spark plug wires? A failing wire will cause a miss.

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Yep, they're fine - checked 'em with an ohm meter and the resistance is well within specs (as noted in my original post...... )

I even swapped in a donor wire from a spare set on the missing cylinders and it didn't change anything.

I'll know more tomorrow - my old radiator had so much calcium and mineral deposits clogging the core, the repair guy couldn't rod it out. He left the right tank off and showed me - it was 70% blocked. Got me wonderin' how the engine got any circulation as it was.....

Got a new Modine ready to go in. This certainly was a BIG part of the problem......

Things are beginning to look better. I think that with this repair, and some 34" tires for the dyno test, I should pass this time (said with fingers crossed.....)