Failed smog test.High NOX

[johnj92131]

Found a hole in the stock header that had been repaired by a previous owner near the collector. New factory header kit is $400 and 4 hours labor. May or may not solve the problem. Going to take the truck to a muffler shop tomorrow an see about patching the hole on the cheap.

Truck is a 91 4.0 new header has to be CARB complaint.

[mikekaz1]

I'm so happy MA doesn't do that crap

[schardein]

http://www.rockauto.com/en/catalog/jeep,1991,comanche,4.0l+l6,1181775,exhaust,exhaust+manifold,5860

 

Rockauto has a replacement manifold that says it is CARB approved for ~$130.  (bottom one)

 

I don't know what a factory header kit consists of, but if it is an exact replacement, then it will crack like ALL the factory 4.0 manifolds do from 1991 to 1999.  In 2000 they changed to a 2 piece exhaust manifold which solved the problem.  

 

I've used two of the re-designed aftermarket manifolds like the one I linked above.  I got both of them from the junkyard and they are still going strong.  Every factory type manifold I have looked at in junkyards was cracked at the collector.  When I replaced the one in my MJ, it was cracked on the outer tubes also.  Factory manifolds are junk and should be replaced.  Use the aftermarket type with the "bellows" on the outer tubes and it should be a one time expense.

 

I don't know how mechanically savvy you are, but I can change out an exhaust manifold on a XJ/MJ in a Saturday afternoon.  The 4 hours you have been quoted is about right.  First time, it took me a little longer.  

[Jeepman]

Just replace it with a Rock auto or ebay part and not the expensive dealer part which is likely just from the local autoparts store and not actually a MOPAR part...

 

 

The factory Maifolds and even aftermarket headers crack (the factory manifold is not a header allthough its close) because of running lean at WOT so once replaced with an OE replacement or an actual header make sure you

upgrade the injectors and the cracking issue will be no more...

[HOrnbrod]

Better yet install a flex joint in the exhaust pipe and the cracking issue will be no more...

[shelbyluvv]

I just swapped my craked header for a $86 Amazon manifold.

[johnj92131]

The muffler shop will fix the exhaust manifold for $280 including labor and I pick it up on Monday.  Not worth 4 to 6 hours of my time right now.  We are right in the middle of a kitchen renovation.   Next, I will need a new oxygen sensor.  Amazon lists these as fitting the 91 Comanche 4.0:

 

http://www.amazon.com/s/ref=sx_as?rh=n%3A15684181%2Cn%3A!15690151%2Cn%3A15719731%2Cn%3A15730551%2Cn%3A15730891&qid=1458504689&vehicle=1991-42-348-20----7-3330------1-1

 

Any one with some experience on these?

 

Also, good tip on larger fuel injection units, thanks,

 

New headers will come when the current 4.0 gets replaced with a stroker.  Same thing with the flex tube in the exhaust.

[HOrnbrod]

The NTK 23023 O2 sensor is the one you want - same as OEM but cheaper.

 

For injectors the Bosch 0280155703's (so-called Neon injectors) are good for a stock 4.0 running with the stock FPR. When stroker time comes you can use them again with an adjustable FPR to bump the pressure up 10psi.

[johnj92131]

Got the truck back from the muffler shop on Tuesday.  Sure is a lot quieter.  Now I hear the the belt squeeling. 

 

After checking the blink code faults (thanks to Don for his post on the Blink Codes), I have a code 27 which indicated a Fuel Injection control circuit issue, and a code 12 because the battery was disconnected and replaced with a new one.    Have not yet ordered a new NoX sensor and am thinking I should disconnect the battery over night to try and clear the error code 27.  If that works, I will take the truck back for a smog retest.  If not, then I will replace the NoX sensor and see about getting those Neon injectors.

[HOrnbrod]

Code 27 (From NAXJA)

It is probably a non-firing injector.

You can do a very quick check to determine whether the problem is in the injector or the harness, by running the engine, and unplugging the injector you suspect is bad. If it's a bad one, nothing will change. If it's a good one, the engine will briefly bog, then recover. Now swap the connector that tested bad with its nearest neighbor, start the engine again, and repeat the test. If the same plug is dead, it's the harness. If the same injector is dead, it's the injector.

Check voltage at the injector plug, and resistance of both positive and negative lines. This system switches the negative side, and positive is constant-on with ignition, supplied via a line with branching splices to each injector plug. The splices can go bad and give you low voltage at the injector. You should check resistance of the pos. line back to the connector at the coil, and the resistance of the neg. line back to the PCU.

Injector 1 goes to pin 16 on the PCU. #2 goes to pin 15, 3 to 14, 4 to 13, 5 to 38 and 6 to 58. The positive line to all injectors is dark green/orange, and traces back to the ASD relay, as well as one of the pins on the coil/distributor plug. With ignition on, engine off, you should get a full 12 volts between the hot terminal on the injector plug and ground. If it's a bad splice, it might start out relatively good when cold, and deteriorate as it heats up. If you have a bad wire or splice in the harness, it's not hard to slice it open and bypass the bad part.

 

Clearing error codes and removing residual memory

1. Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.
2. Reconnect the Battery Cable
3. Turn Ignition Switch to the "ON" position but DO NOT start the engine
4. Turn Headlight "ON"
5. Turn Headlights "OFF"
6. Turn Ignition Key "OFF"

The PCM Adaptive memory has now been flashed, or erased from the PCM.

[schardein]

Got the truck back from the muffler shop on Tuesday.  Sure is a lot quieter.  Now I hear the the belt squeeling. 

 

After checking the blink code faults (thanks to Don for his post on the Blink Codes), I have a code 27 which indicated a Fuel Injection control circuit issue, and a code 12 because the battery was disconnected and replaced with a new one.    Have not yet ordered a new NoX sensor and am thinking I should disconnect the battery over night to try and clear the error code 27.  If that works, I will take the truck back for a smog retest.  If not, then I will replace the NoX sensor and see about getting those Neon injectors.

By NoX sensor, do you mean oxygen sensor?

[64 Cheyenne]

Got the truck back from the muffler shop on Tuesday.  Sure is a lot quieter.  Now I hear the the belt squeeling. 

 

After checking the blink code faults (thanks to Don for his post on the Blink Codes), I have a code 27 which indicated a Fuel Injection control circuit issue, and a code 12 because the battery was disconnected and replaced with a new one.    Have not yet ordered a new NoX sensor and am thinking I should disconnect the battery over night to try and clear the error code 27.  If that works, I will take the truck back for a smog retest.  If not, then I will replace the NoX sensor and see about getting those Neon injectors.

 

Suggest you check the harmonic balancer, make sure it is not separating and rubbing on the front of the timing cover. Sometimes sounds like a bad belt.

[johnj92131]

 

Got the truck back from the muffler shop on Tuesday.  Sure is a lot quieter.  Now I hear the the belt squeeling.

 

After checking the blink code faults (thanks to Don for his post on the Blink Codes), I have a code 27 which indicated a Fuel Injection control circuit issue, and a code 12 because the battery was disconnected and replaced with a new one.    Have not yet ordered a new NoX sensor and am thinking I should disconnect the battery over night to try and clear the error code 27.  If that works, I will take the truck back for a smog retest.  If not, then I will replace the NoX sensor and see about getting those Neon injectors.

 

Suggest you check the harmonic balancer, make sure it is not separating and rubbing on the front of the timing cover. Sometimes sounds like a bad belt.

 

 

Good thought!   But I/we put some belt lube on the belt, sound goes away for a short time.  Did this several times to verify the issue.

 

schardein - Yes, should have said the 02 sensor!  Thanks for catching that.  I can see newbie reading my post and wondering what I am talking about.

 

Don, Thanks for the how to on quickly clearing the error codes.  And for the pointer on Code 27.  If the code comes back, I will use the Fluke to do the suggested check.  Also have a request in to Dirty Jeep Guy for a rebuilt set of the 703 injectors.  Time to replace them anyway.

[schardein]

I pulled 703 injectors out of Dodge Neons at the junkyard and took them home and plugged them straight into my XJ and MJ without even a wipe down.  In both cases I noticed a slightly smoother idle. 

 

In both cases I also swapped to the later style intake, aftermarket exhaust manifold, new O2 sensor, and did a basic tune-up (dist cap, rotor, plugs, wires, air filter, engine oil change) at or about the same time, so any other changes would be hard to attribute to the injectors alone.

[johnj92131]

The Jeep passed the recheck this morning.  Not by much, but it did pass, so I am good for 2 more years.  Only thing I did was have the manifold rewelded.  New manifold (flex pipe also) and new O2 sensor will come when the stroker goes in.  New Neon injectors will go in ASAP and transfer to the stroker.  Need to find a couple of brackets that are required to use the 99 and later intake manifold (power steering bracket?).  Then send the the spare throttle body to be bored out. 

[HOrnbrod]

Need to find a couple of brackets that are required to use the 99 and later intake manifold (power steering bracket?).

 

I got the brackets at the yard along with the pump from a wrecked low mileage 04 TJ . Worked great with the ZJ steering gear.

[johnj92131]

 

Need to find a couple of brackets that are required to use the 99 and later intake manifold (power steering bracket?).

 

I got the brackets at the yard along with the pump from a wrecked low mileage 04 TJ . Worked great with the ZJ steering gear.

 

Do I need to get the pump to go with the brackets?  Or can I reuse the old pump?  ZJ box is a bit quicker ratio I know, but are there any other advantages to the swap if why I have is working OK?  Seem to recall reading there were some other advantages, but don't remember the specifics at the moment.  Down side is more work and more $$$.  Should have bought the ZJ steering box from MJRemi when he was moving to Oregon last year. But I had enough on my plate with the Passat TDI.  Now that the Passat is mostly done and has new paint I can spend more $$ on the Comanche (or replace it with a Tundra).

[HOrnbrod]

You can reuse your existing pump with the newer brackets. I just grabbed the pump too since it was only $5 more. Since it was newer, I used the TJ pump, but either is fine. I put the quicker ZJ box on about a year or two later and liked it a lot more than the stock MJ unit.