I woyld like to understand the theory on plug temperatures. Perhaps I was given the wrong ones and by simply going back to the stock heat rating it may help with my issue. I would just put back my stock injectors but I am sure they are gone by now. I have a spare set of 703's I would gladly trade for a set of stock injectors. when I put in the 703's I myself didn't notice any difference except a slightly better throttle response.

 

If you couldn't pass smog with a stock thermostat you've got another problem...

Spark plugs act as heatsinks into the combustion chamber. The heat range indicates how much they'll remove. Colder plugs remove more heat. The 4.0 is very finicky about heat range, this is why a lot of fancy aftermarket junk doesn't work. Stick with NGK ZFR5N or Champion RC12ECC.

If replacing parts with the OE spec, and you still have problems, the solution isn't "go aftermarket". Find and fix the problem.

As for the fuel injectors, I believe the 703s actually send a little bit MORE than the OE junk, but they atomize it better. If anything during the first week or two you should see it take longer to warm up as the PCM adjusts to the new rate (different case in Renix though).

Have you tried reinstalling the stock injectors to see if its fixed?

 

Thats a pretty thick oil there. Could be causing extra work for the engine. If you have an oil pressure problem, dont band aid it with thicker oils. Just find and fix the problem. With all of the info gathered I would have to say you have an internal engine issue.

 

I was overheating...come to find out all the bearings were down to the copper. Just something to think abour

 

I failed smog terribly the first time, so I replaced the cat and got super close to passing.



As you can see I barely failed the low speed NOX but passed the high speed with flying colors. After much research and ABSOLUTELY TERRIBLE ADVISE/Suggestions on this forum and others, I finally figured out that excessive combustion temps cause a high NOX reading. Since the cherokee has no distributor to advance/retard, no egr and a computer system that will try and compensate for any changes you try and make I had no choice but to change the thermostat to a 180* and change the plugs to a lower heat range.

Then it passed easily, further more I picked up about 1.5 mpg better economy, it idles smoother and runs better at high elevations.

I believe the 703 injectors actually squirt slightly less fuel but better atomized. At least on paper that's what the numbers suggest.

 

My pressure wasn't too bad before it was just a bad idea to run the thicker oil. I hope there is no problem with the motor It only has 130k

 

Why are you on this forum if the ADVICE was terrible? Just curious.

 

Please direct your question to gary briggs who posted that. I don't want anyone to think I have an issue with the advice given here

 

This was a year ago so i cant remember eerything, I kept posting results after every pre test, everyone kept insisting it was a sensor or an exhaust leak. All of which I knew was BS, if it was a sensor more than just the low speed NOX would have failed, and you can hear an exhaust leak 10 miles away.

The suggested fixes ranged in price from 5$ to hundreds of dollars all of which would have been a waste of money, my jeep was running really well prior to the test. Since I bought it with 160k miles, I was steadily replacing parts with high quality stuff from napa. Some of it out of necessity and others because the were factory original so I was being pro active, replacing before it failed.

The fix I spoke of that ultimately worked, was 13$. And it runs better than ever.

 

Sorry dude but a stock thermostat wasn't causing higher-than-stock combustion chamber temperatures. These things pass emissions tests in factory configuration when completely maintained. In fact the current emissions testing criterion are EXTREMELY generous.

But any way that's a thread hijack that doesn't help the OP.

 

Yeah, that's gotta be some strange coincidence. The factory ran them that hot to insure emissions compliance.

 

I want to understand how a spark plug can change combustion temperature.

 

I never said that it did cause higher combustion temps, what I did say was with 703's I had excessive combustion temps that resulted in a high NOX reading. I changed plugs and thermostat, while running 703's, and my engine ran better and cooler, with an increase in mpg.

The thread is about 703 injectors, so how is this a hijack?

Further more the county I live has pretty strict smog restrictions, I could move 30 miles away to a different county and have no smog restrictions at all. The emission test it went through in 1995 might be a bit different than the one being done 18 years later. It's so hard to pass the state will pay you for your car if you can't get it to pass.

 

Gary, Salad wasn't saying you hijacked anything but that he touched on emissions testing criteria and that itself would be a hijack.

And I don't consider what you contributed to be a hijack either so lets move on please.

Do you feel that you had to change plugs and your thermostat because you went with the 703's?

 

Found the information I was looking for...

Neon 703 injector:
21.5lb/hr @ 39psi
24.1lb/hr @ at 49psi

Slightly higher static flow. Until your PCM updates the trim tables via feedback from the O2 sensors you actually run slightly richer (cooler)

Check this out: http://www.ngksparkplugs.com/tech_su...k_plugs/p2.asp

Have you cleaned the combustion chamber? Running the right plugs?

Plugs at the same time? Seems a LOT more likely to be related to whatever problem you were experiencing.

NOX forms at temperatures over 2400 degrees. I highly doubt that lowering the minimum temperature of the engine coolant by 15 degrees, and not modifying the rest of the system to reject heat at a faster rate, could possibly have any meaningful impact.