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94 Xj 4.0 engine problems! :(

Old 05-17-2019, 12:33 AM
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Default 94 Xj 4.0 engine problems! :(

So my 94 xj 4.0 has been acting up. (Ongoing problem since i got it been working on this for 2 years now)
It has obd codes 27 and 17.
When i got it it had the 746 injectors and had the obd code ran bad. I put the 703 injectors on it and it runs better but you can feel the misfire more.
Occasionally before i swapped the injectors it wouldnt start unless i floored it if i drove real quick to the store and turned it off.
Now sometimes it has a hard time starting unless i give it gas. Not all the time though.
It stalled on me today after driving home from work stopping at my friends for about 20 minuites.
I started it it didnt start, cranked again got it to start pressing the gas. I go around the u shaped road to the stop sign it dies. I start it drive the rest of the way home about 1/2 mile pulled in and read the codes.
Now i have theories on the code 17 because it smells like coolant sometimes when its hot but see no leaks. I replaced everything in the past but the radiator, heatercore and waterpump. I plan to replace all those and with a new thermostat.

On the obd code 27 now...
Cylinder 5 (second one back i believe its #5) the fuel injector wire failed voltage test i saw bad wires replaced the pigtail now it has the right voltage as the others still misses and the injector did not seem to fire with sethoscopes so i may buy a new set and replace according. They all had the same resistance in the injectors.
I was thinking of chasing the wires back to the pcm and testing everything from there.
I do not have a fuel pressure tester i plan to buy one.
New fuel filter as of last spring
I plan to check my o2s,tps,cps,map,iac,fuel pressure regulator. Maybe have to replace the pcm.
If i can find new wire harness or rebuild mine i will.
I've checked my grounds.
It has new cap rotor plug and wires. Oe style except cap and rotor is accell. I will swap to mopar. My mistake i learned better.
It sounds like a lifter tick so i will be looking into fixing all that also as time goes on with better research.

Any help is greatly appreciated! I study Xjs every single day as this is my favorite vehicle i never want to get rid of it and want to master the art of Xj
Thank everyone of you so much im glad to help any way i can. I love the challenge and opportunity to learn!
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Old 05-17-2019, 10:35 AM
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Anyone?
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Old 05-17-2019, 11:50 AM
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#5 is the second one from the back. Second one from the front is #2. Lifter tick is designed into the motor because it has no provision for valve lash adjustment. In other words, it's normal. Get used to it. If it's only one and loud, it's probably a collapsed lifter. Do a compression check to see if the cylinder that's missing has low compression. It could have a bad valve seat seal, especially if the miss disappears at driving speed.

You can "rent" a pressure tester at most auto parts stores. At Autozone, you buy it, then get your money back when you return it, provided you didn't damage it.

The injectors are powered up with 12v all the time it's running and they are grounded thru drivers in the PCM when required to spray fuel. Check the PCM plugs for loose, bent, or burnt pins.

The antifreeze smell could be from a slight seepage leak that evaporates so you don't see it. That's usually the waterpump shaft seal.

Last edited by dave1123; 05-17-2019 at 12:01 PM.
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Old 05-17-2019, 04:08 PM
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Thank you. Yes i already knew the lifter tick is normal just compared to the other 2 xjs its bad so i wanted to check it all out. I do not believe that is my problem just a potental symptom of a chain of events.
If my pcm or ecu as mopar calls it were to be bad could i get one from a 1995 or a 1993? Given they have the same high output 4.0, aw4 tranny, 242 tc and is obd1?
I am not having much luck besides ebay when looking for replacement parts for the ecu.
Not saying im going to throw an ecu at it just want to know given the circumstance it is bad.
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Old 05-17-2019, 10:16 PM
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ECU needs to be the matching part number. Probably the same over several years.
It will run with the wrong ECU (my 95 had the wrong one when I bought it), and on a pre-obd2, maybe less important, but the general rule is - same part #.

Agree with Dave on the small coolant leak evaporating. You can get a pressure tester for rent same as the fuel one. The coolant tester will let you pressurize the system and it makes finding small leaks MUCH easier.
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Old 05-18-2019, 06:06 AM
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Originally Posted by Romans715 View Post
Not saying im going to throw an ecu at it just want to know given the circumstance it is bad.
Start with cleaning up your grounds. All of them, but especially the grounding plate that is jut forward of and below the distributor.

It's pretty close to free, and will often solve unsolvable problems. Not always, of often enough to be a good first step.

See my sig, #1.
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Old 05-18-2019, 09:05 AM
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746 injectors are an upgrade for Renix, not HO engines.

DO THE GROUNDS!!!!
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Old 05-18-2019, 09:57 AM
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The fist thing they always say in the repair books is, don't begin electronic diagnosis until looking at all the basics (Spark plugs, vacuum leaks, grounds, connectors, EGR, etc)

I would recommending removing the plugs and see if they all look the same, and if any look different, HOW do they look different. If one is really clean, you might be having the beginnings of a bad head gasket in that cylinder (Thus adding more pressure to your radiator and forcing out some anti-freeze smell). Maybe not, ...but it's a basic thing to look at. Vac hoses too. Do a vacuum test.

It sounds like you have a plan on the lifter, so, I won't address that.
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Old 05-18-2019, 12:35 PM
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Thank you all for your help.
So i still need to run to town and get a fuel pressure tester but i cleaned up the grounds by the ecu and on the dipstick tube. One terminal broke so i spiced in a new one. I didn't do a compression test or look at my spark plugs yet since im about to head out for the afternoon. I did check voltage and resistance for the injectors/inj wires. The resistances fluctuate between 13-16 ohms for the injectors. *Part number 703*
All the inj wires except cyl 2s were at 14v which is weird to me considering everything ive read they are supposed to be 12v. Cyl2 was at like 300mv-4v constantly fluctuating
I am considering looking over my wiring from that terminals repair then tracing the voltage back.
I need to learn its current route i am looking over the chiltons and haynes manuals for any more information and diagrams for electrical

I do need to pick up a new vacuum elbow for the pressure regulator while i am at it. I believe its a little loose but not enough to cause serious issue but enough i will replace it for what like 80 cents

I have never tested the pins on an ecu before. i know pin #15 is for injector 2 so i want to check that and wherever the wire drk grn/org wire connects.

I will be researching that 14v issue in the mean time
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Old 05-18-2019, 07:08 PM
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Originally Posted by Romans715 View Post
All the inj wires except cyl 2s were at 14v which is weird to me considering everything ive read they are supposed to be 12v. ......

I will be researching that 14v issue in the mean time

12v is what is known as the "nominal voltage", meaning, IN NAME ONLY. Your 14 volts is just fine. When your alternator is charging correctly it should out out 13.8 volts. Some run a bit above or below that.

If it were actually reading 12 volts, you'd have a dead alternator.


IIRC, the ECM grounds on the plate on the side of the block, just forward of and a bit below the distributor. Make sure that ground is good.
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Old 05-18-2019, 07:56 PM
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Ok sweet. And yes earlier today i cleaned that ground up. Surprised i never noticed it. Still acts the same but it needed it as soon as i started using sandpaper one of the terminals tore off like nothing
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Old 05-19-2019, 02:52 PM
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Another question guys! How do i properly test the pins on my ecm as from my research tells me that it is on the ground side so do i test for voltage and have it plugged in and stab the wire with a hershman clip on my mulitmeter next to the ecu or should i check for resistance in the pin itself or...... I am not sure maybe i have it backwards in my mind i will keep looking.
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Old 05-19-2019, 04:06 PM
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Originally Posted by cruiser54 View Post
746 injectors are an upgrade for Renix, not HO engines.

DO THE GROUNDS!!!!
Yes my friend put the 749 before i bought it from him. Later found the 703 is for my years xj put them in and it ran so much smoother but when it missed it was more noticeable and has stalled on me a couple times barely enough fuel flowing to get it to start like very low rpms moving up and down and dieing off try again maybe hit the gas a little and fires up after a few moments it balances itself out with the miss affecting the movement of the gauge as it occurs
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