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Engine missfiring when accelerating and at idle

94sport

NAXJA Forum User
Location
Whittier
So my jeep was running a bit rough and I suspected the stock injectors needed upgrading. I since installed the 4 hole injectors, new fuel pump, new fuel filter, new fuel regulator, new cap & rotor, new spark plugs & wires. Only engine code is 12 because I disconnected the battery to weld a crack I found on the exhaust manifold. Injector seem to be clicking when I listed with mechanic stethoscope. I am stumped as to why this thing is not running well because compression test was between 167-179 psi on cylinders?
 
My wife's Rubicon showed the same symptoms.
I used a bluetooth obd 2 scanner in test mode to
determine a tps fault. I tried replacing the coil rail
which indicated a low resistance reading across a
secondary coil. This wasn't the culprit.
Try to find the cause before you take the shotgun
approach. Ot could save some cash.
 
My 4.0 is OBD1 so a scanner is no help. Thinking my timing chain might be stretched since it’s been 100k since I last replaced it or the crack in my exhaust manifold may have damaged my O2 sensor. I plan to drive it a while to see if the computer throws a code.
 
Should probably post in OEM tech.

However, start by finding which cylinder it is. Buy a cheap infrared temp. gun at harbor freight. Check each pipe while running.....looking for one that is cooler than the rest. Then you can test compression, spark plug, plug wire, and injector for that cylinder.
Test by moving one part at a time (trading with another cylinder). When you get to the faulty part, the colder pipe will change with it.
 
Should probably post in OEM tech.

However, start by finding which cylinder it is. Buy a cheap infrared temp. gun at harbor freight. Check each pipe while running.....looking for one that is cooler than the rest. Then you can test compression, spark plug, plug wire, and injector for that cylinder.
Test by moving one part at a time (trading with another cylinder). When you get to the faulty part, the colder pipe will change with it.

Thanks, I'll try the heat gun!
 
Was the Ex-manifold/O2 sensor installed on the block when you welded? Might have fried a sensor or ground?

But it sounds like a bad TPS or ground or connector, or a Vacuum leak at the MAP sensor vacuum hose between the MAP and throttle body. Both would common causes.

So my jeep was running a bit rough and I suspected the stock injectors needed upgrading. I since installed the 4 hole injectors, new fuel pump, new fuel filter, new fuel regulator, new cap & rotor, new spark plugs & wires. Only engine code is 12 because I disconnected the battery to weld a crack I found on the exhaust manifold. Injector seem to be clicking when I listed with mechanic stethoscope. I am stumped as to why this thing is not running well because compression test was between 167-179 psi on cylinders?
 
oh also. since your is a 94. make sure you do not still have the dreaded fuel pump ballast.
if you do. Smash it with a hammer and solder those two wires together... and curse the man who decided 12volts to the fuel pump is too loud... meh.
 
Thanks everyone for the advice! After throwing lots of time, money, and parts at this I dropped the jeep off at a local mechanic to diagnose this afternoon. I have 2 XJ's and this one is a 92 limited.
 
So the mechanic said the 4 hole injectors I bought as a upgrade were actually causing a run rich condition and the fuel pump I installed from AZ he said was not delivering enough fuel pressure which I doubt however I let him swap it out and my O2 sensor was not working because of a relay between the fuse box and battery that went bad.

My jeep now has a new fuel pump, fuel regulator, fuel filter, clean stock injectors, cps, cap, rotor, wires, plugs, oil & filter, alternator, and a catalytic converter.

I hope I get another 100,000 miles out of her.
 
Just out of curiosity, what 4-hole injectors did you have in there that were overfueling? I have Bosch 703s in my '92 and they work great, no misfires.
 
Yep, the link works. Those look like the ones I have. In my case, the first set I got had some sort of problem that caused them to flood the cylinders with fuel; had to get the seller to send me a replacement set and they've been fine. Maybe the 703s you got had a problem.

Oh, and for OBD-1 jeeps, you can do the key trick to get the check engine light to blink out any stored codes - just do an on-off-on-off-on, then be ready to count blinks (or video it with your phone and count them out later.
 
These are the ones I bought off of eBay. Hopefully you can get the website from this:

https://rover.ebay.com/rover/0/e110...w.ebay.com/ulk/itm/273186122082&sojTags=bu=bu




The pricing and pictures look like Cheap chinese knocks offs, despite the listing saying oem. They probably flow a bit more than stock, and not having a working O2 sensor the computer couldn't adjust the fuel trims to compensate. Unfortunately, you spent a lot of money and time just to find out it was a bad relay.
 
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