Moved From Introductions:

Thanks for responding. I purchased a 92 Jeep YJ for $2200 and spent 3 years and
$11,500 rebuilding and upgrading it. I learned a lot of valuable info that can be utilized
across both jeep platforms so I'm not new to the older Jeep rebuild world






I did check the correct wire configuration. Thanks for the insight. I haven't pulled the
distributer out yet. What should I be looking for? I been trying to educate myself on
the Cherokee XJ and have been doing a lot of research on the subject. I have a few
more questions.

Would any of these cause the random cylinder misfire across all cylinders?
1) Leaking valve cover gasket
2) Bad fuel regulator
3) Weak or failing fuel pump
4) Low Voltage from a coil.
( My 96 XJ only has 1 coil for all 6 cylinders that I know of)
5) Bad or failing PCM
6) Timing
7) Failing and cracked wiring harness
( the 96 XJ had the injector wires being routed directly over the intake manifold and
are prone to heat damage)

When I replaced all 6 injectors, I did upgrade to the 4 pin hole injectors for better fuel
atomization and a cleaner burn.

 

OK I tested the voltage from the injector plug back to the PCM and I'm get between 3.4V and 4.2V.

Injector-1 - 3.4V
Injector-2 - 4.9V
Injector-3 - 4.1V
Injector-4 - 4.3V
Injector-5 - 4.1V
Injector-6 - 4.2V

Not sure what voltage from the PCM to the injectors should be or what they need to fire.

 

Voltage is supplied by the ASD relay.

The PCM grounds the injectors when it's time to fire them.

Check your ground. Check your grounds. Check your grounds. And then check your grounds. And then check all of them in the engine bay. Check cables. Check connections. If you are just looking at them, you are doing it wrong. See my sig, #1.

And check your grounds. See Cruiser54's tips.

That voltage is way low, though.

Have you verified fuel pressure with an actual measurement with proper gauge?

 

Using a multimeter on the "voltage" setting, hook one lead of the multimeter to the positive (NOT negative) battery terminal and test both pins of the removed injector plug with the other lead while the engine is running. One wire from injector is at 13V, and the PCM periodically shorts the other injector wire to ground to open the solenoid. So on the multimeter (relative to the positive battery voltage), one pin should read at 0V and the other should read a little under 2V. For more info see https://www.cherokeeforum.com/f2/how...cm-95-a-248325.

 

If I had to venture a wild guess, methanol goo has fouled the injectors and they're not atomizing properly. Sitting over the winter, my lawnmower's carburetor also suffers from the goo if I don't run some non-methanol gas through it to winterize it. Perhaps some fuel additive is needed to clean them out or, worst case, replacing them all.

 

A true misfire is one of three things: loss of adequate spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression.

Being a misfire on all cylinders does basically rule out the common reasons for abnormal compression being the reason, to help rule that out.

I have to think it does sound like it is maybe related to a fueling issue too? Possibly it could be the fuel injectors as the reason?

How are the plugs doing? They may be able to show you something? Rich or lean? Carboned up or oily wet? Evidence of pre-detonation? Are the spark plugs providing an adequate spark?

You could check the fueling by the fuel rail psi tests, and see how it looks?

An off the wall reason for all of the cylinders to show as misfiring could potentially be caused by a loose or slipping serpentine belt.. a pulley?
(Thats wrong.. A timing belt as an example could. I mixed it up in my head)

 

Methanol does not affect voltages.

 

A true misfire is one of three things: loss of adequate spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression.
Being a misfire on all cylinders does basically rule out the common reasons for abnormal compression being the reason, to help rule that out.

I have to think it does sound like it is maybe related to a fueling issue too?
Possibly it could be the fuel injectors as the reason?
I upgraded all injectors to New EV6 - 4 pin hole injectors.

How are the plugs doing? They may be able to show you something? Rich or lean? Carboned
up or oily wet? Evidence of pre-detonation? Are the spark plugs providing an adequate spark?
Plugs are new Autolite coper core 985's. Dry, no carbon buildup and gapped at .035
Cap, Rotor and Wires are also all new

You could check the fueling by the fuel rail psi tests, and see how it looks?
How would I test the fuel rail's pressure? When I changed the injectors and removed the rail it was under good pressure but I have no
way of knowing the PSI or how to test it.

I am getting a code 27 (The injector circuit is not syncing with the input signal.)
I'm leaning toward installing all new pigtails with new plug ends for new 4-pin hole injectors. Heat corrosion from age cracks and shorts these wires out that were located directly over the intake manifold. When I tested the injector plug back to the PCM with my multi meter while the engine was running, I was getting pulse readings no higher than 4.2V. I believe it should be 7.2V on the hot wire and when grounded by the PCM, 12.4V -to- 13.9V. This indicates to me that the injectors wiring back to the PCM is either cracked, grounded or shorting out and not providing proper voltage to open and fire the injectors, causing the all cylinder random misfiring.

Any Thoughts?

 

I'd start with fuel pressure. Not saying that is your problem but gotta rule it in or out early in the troubleshooting process or you could be chasing your tail.

Call your local parts stores and see if they will rent you a "fuel pressure gauge". Most parts stores do this and it is inexpensive to rent this gauge. It simply goes onto the schrader valve on the fuel rail (looks like the valve that you fill a bike tire with air).

Compare your reading at idle to factory spec. NOTE: 96 was the year of change for the fuel system on the XJ. If you have a fuel pressure regulator under the hood, then you have the "old" system and the fuel pressure spec is 31 psi. If you have no regulator under the hood, you have the "new" system and the fuel pressure spec is 49 psi, plus or minus 5 psi.

Let us know what you find...and oh yea, as BlueRidgeMark mentioned, I would freshen all engine grounds. Can't tell a thing by looking at them.

 

Tomorrow I pull all the grounds apart and inspect them. I'm going to purchase a fuel pressure testing gauge tomorrow and
also trst the fuel pressure at the rail to either rule in or out a fuel delivery problem.
Ill post up my rresults

 

OK, Here are the results . . . .

Grounds Check
I took apart the grounds and cleaned them. I didn't see any major damage or corrosion so I reassembled them.

Fuel Rail Pressurization Test
Key On, Motor Not Running - 30 psi
Motor Running at Idle at 600 rpm's - 41-43 psi
Motor Running at 2500 rpm's - 41psi

Looks like I can rule out a fuel delivery problem.

Cylinder Compression Test
Cylinder 1 - 144 psi
Cylinder 2 - 145 psi
Cylinder 3 - 145 psi
Cylinder 4 - 151 psi
Cylinder 5 - 152 psi
Cylinder 6 - 89 psi

Looks like I have a Cylinder 6 compression problem. I put a tablespoon of oil in cylinder 6 and retried
the test. The 2nd test I only gained 13 psi from 89 psi to 112 psi.

What's next? Pull the valve cover and inspect Cylinder #6

 

I retested all the injector wires from the injector plug back to the PCM. This time I clamped a test lead to the Neg (-)
battery terminal and clipped it to my multi meter to get a better ground. I then tested each plug. Here are the results.

Injector 1 Plug End Back to the PCM - 13.86V
Injector 2 Plug End Back to the PCM - 13.87V
Injector 3 Plug End Back to the PCM - 13.87V
Injector 4 Plug End Back to the PCM - 13.86V
Injector 5 Plug End Back to the PCM - 13.87V
Injector 6 Plug End Back to the PCM - 13.86V

All almost textbook identical so I can rule out the plug end, wiring and the PCM.

OK Here's where we stand . . . . . .

Ruled out Fuel Pressure - Good at 41 psi
Ruled out bad fuel pump and regulator
Ruled out Grounds - Took apart, cleaned and put back together
Ruled out Bad Injector wiring - Tested voltage on all injector plugs back to the PCM - Good at 13.87V
Ruled out Bad PCM
Ruled out Cap, Rotor, Wires and Plugs - All Replaced / New
Ruled out Bad Injectors - All Replaced / Upgraded all injectors with New 4-pin hole EV6 injectors

I narrowed it down to bad compression on cylinder #6 with low compression at 89 psi
Since it's drivable, I'm going to look for a low dollar head to send out and get valve job done on it to minimize down time.
Once I get the machined head back I'll swap them out.

I'll post up with the progress.

 

You for sure have a problem with cylinder #6 compression.

But 41 psi at idle of fuel pressure does not rule out a fuel problem if you have the newer style fuel system (with no fuel pressure regulator under the hood).

The fuel pressure spec for the new system is 49 psi, plus or minus 5. That leaves you at 44 psi being the lowest end of the spec. You are below that at 41 psi. You may have marginal fuel pressure which could still be the root cause of multiple cylinder misfires. An internal problem with only cylinder #6 should not result in all the misfire codes you are seeing on all the other cylinders.

I think you could have two things going on here......I would also get a meter and a manual and test both primary and secondary resistances on your ignition coil.

Good luck and keep us updated.....

 

I did a cross reference on my stock injectors (Chrysler 53030778) working PSI and you're correct, It is
49 psi so I'm running low on fuel pressure at the rail. I'm assuming this in a failing fuel pump? where is
the fuel pump located? Is it in the fuel tank?

So now I'm dealing with 2 problems.

What's a general price for a valve job?

 

[QUOTE=jahewitt;3577312 I'm assuming this in a failing fuel pump? where is
the fuel pump located? Is it in the fuel tank?
[/QUOTE]

somewhat unwelcome news for you on the '96 fuel pump situation...it is an "one off", just for that year.

it consists of a post update pump, pre-update regulator (with no vacuum hose) and guage senders all together in one unit in the tank