Ok, it’s been a while since I’ve posted but I’ve still been enjoying my XJ until this weekend. I was driving through the mud and I swapped my alternator. I replaced the alternator and it was working fine for maybe 20 miles until the engine suddenly stopped running as I pulled into the driveway. I tried to turn it on and it cranks but won’t start. I have gas in it. The only other issue I had was that it was shifting at higher rpm and it wouldn’t go into overdrive. Could this have something to do with the TPS sensor? I was wondering if that caused the shift issues. I need to look into it more but I’m wondering if y’all have any suggestions.

 

The shifting problem could be related to the TPS. But first things first, let's get it running.

4 things needed.

1. Compression and assume that is good as it was running until it wasn't.

2. Fuel. Must be tested with a fuel pressure gauge. Rent one from your local parts store if you don't have one. You need approximately 31 psi of pressure to start your 1992 vintage 4.0 liter engine. Then disconnect the vacuum line leading to the fuel pressure regulator and pressure should jump to 39 psi

3. Spark. Test for it. Pull a plug. Keep plug attached to the wire and place the plug electrode near a good engine ground. Have a buddy crank the engine over. You are looking for a strong, BLUE, snapping spark. Yellow/orange/white could be a weak spark which can be caused by a failing ignition coil, the coil can be tested for both primary and secondary resistances with a manual an a meter.

4. Injector pulse. Can be tested with a simple "noid light", available at any parts store.

Start there, good luck and keep us updated!

 

So after I made this post it started again, not sure why, and I was driving it around on my friends property (large plot of land in the country). The shifting issue was still present and it was revving up to 3500rpm before shifting gears. After driving it for a while I turned it off and it wouldn’t start again. If I let it sit for maybe 20 minutes or so it will start again though.
Im thinking about replacing the TPS and seeing if that helps anything.

 

The TPS may help with shifting. There is a testing technique if you so choose but if you replace, get a MOPAR TPS from Jeep if you replace, there are plenty of junk TPS units on the market.

The TPS is however not likely related to your no start condition. You probably have two separate problems.

Still going to have to TEST your way to a solution on the no start. WHEN it doesn't start, test for spark and test fuel pressure. Don't throw parts at this, let a proper testing based diagnosis lead you to the root cause.

If you are missing spark when it won't start, the crankshaft position sensor could be in play, it is not uncommon for them to experience thermal (heat related) failure.

 

Try just unplugging the TPS and see if that helps. If it's telling the computer it's wide open throttle that'll trigger the flood clearing and no fuel delivery.

 

Just to clarify the issue, since I was experimenting with it this morning, the Jeep will cold start fine, but while driving it stuttered a then shuts off and won’t restart.
This might be related to the shifting issues, I’m honestly not sure.

 

That sounds more like the crank sensor getting warm and failing. That often does not set a check engine code. Shifting is most likely the TPS sensor which isn't sealed very well and really doesn't like getting wet or pressure washed.

 

I checked the codes by turning the key 3 times. I got 3 5 4 5 5. From what I understand, the last 2 fives indicate the end of the codes. What are the other ones? 35? 54? I’m confused about how to interpret them. If it’s 54 (no camshaft signal detected during engine cranking) then would I need to replace the cps? 54 would make sense but I’m not sure what the 3 means.

 

OBD1 codes come in pairs (2 digits). Try and pull the codes again and verify what you have.

https://www.quadratec.com/c/referenc...iagnostic-code

 

Do you know a buddy who has a decent scanner? Would allow you to measure a few things. A bad CPS will shut ya down, but usually won't start back up. Sometimes they do, but often they don't. Also, ohm out the temp sensor and compare to a temp/ohm chart for the xj. Cold reading, and hot. It might have 'drifted' and be telling the computer a different temp than it actually is(delivering the wrong fuel/air ratio). Would be good to know the fuel pressure too. Can you 'hear' the fuel pump operate, those times it doesn't start? Failing fuel pump relays are an issue on these Jeeps.

I'm just throwing some possibilities to check....

.

 

heres what it’s giving me for codes

 

I just tested fuel pressure and it was about 40 psi.

Here it is after sitting for a few minutes. It only lost a few psi which based on the video I’m following means that I’m good.

 

I am going to replace the cps next. I’m pretty sure I have a 54 code, and I’m not getting a spark when I crank the Jeep. Does rock auto sell any decent cps sensors?

 

I recommend the NTK.

I also looked at your vid. The first sequence is very odd that the one flash (the 3rd one) lasts much longer than any others. I'm not sure what it means. Perhaps others with OBD1 systems will chime in.

 

So I replaced the crankshaft position sensor and the throttle position sensor and I am still not able to get it start. I am getting a 12 and a 54 code. From what I understand, the 54 code has something to do with the crankshaft position sensor.
Someone mentioned it might be a fuse. Do we have a camshaft position sensor in a ‘92? I just changed my distributor cap and plug wires.