93 Cherokee Sport:Turning, but not firing.

I have recently done an engine swap and have had the vehicle start, and run for a few minutes. Since then, the jeep will not fire up. It has a long list of whats new. Am wondering what link I am missing, any help is appreciated fellow Jeep lovers.
1993 Jeep Cherokee Sport
Automatic transmission
6 Cylinder 4.0


Jeremy Texas.

Any codes? I'd suspect fuel supply issues if there's nothing showing up in OBD. A bad crank position sensor or a bad cam position sensor will cause no start, but they will usually throw a code. It would be helpful to know if there's a spark. Most failures in the electronic systems here will kill the spark, so if you have spark you can pretty well eliminate a lot of stuff.

If it started and ran, but then wouldn't run after shutdown, you might also want to check for errors in wire routing. It's not unheard of for the crank position sensor wire to be too close to the manifold and end up shorting or melting.

If the vehicle sat for a long time between old and new engines, I'd look closely at things like clogged fuel filter, bad fuel lines, seized fuel pump, etc. A check for fuel pressure would be a good place to start.

You might try dropping a few drops (just a few) of fuel or a squirt of starting fluid down the throttle body and see if it fires up. If that happens, you know you have spark.

If it sat for a long time, you should also make sure there aren't mice in the exhaust and intake, though I'd expect it at least to kick over briefly then.

All very good points. I've had a master mechanic come out a couple of times, and the jeep has done different things at different times.
1)fuel pressure was checked; good pressure ( I still have a new fuel filter ready to go)
2)timing is good.
3)replaced fuel pump relay
4)another time a vacuum hose was unplugged at the sensor (literally it wouldn't even turn)

Am left wondering are the sensors crapping out on me? I have found a way to test that. A ohms and voltage reading for the CPS. A bad CPS would not allow for spark, correct?

appreciate your reply. I have noted your suggestions and will recheck all of them.

I have not replaced the fuel pump, cause it has started and ran. It has started at times using starter fuel.

Luckily mice only ate one wire to windshield washer, have replaced that.

If it starts and runs briefly with starting fluid, then it's getting ignition. That basically rules out the crank position sensor and the cam position sensor, unless they're working intermittently and you just happen to catch them in a good mood (unlikely).

Two areas that the OBDI system will not report on, aside from mechanical engine problems, are fuel delivery problems and secondary spark problems. I'd keep checking the fuel, and make sure the coil is working properly. Double check the distributor too. Bad rotor, cap button, basic indexing, etc.

Don't forget too that the 93 has a fuel pump ballast resistor, so you might want to double check that this is not defective. You can just bypass it.

I've been reading a lot on this site, decided that troubleshooting the thing was worth a shot. Battery voltage 12+ volts. My CPS has a bad ohms reading (O.L). Am looking up fuel system trouble shooting. I'm sure the fuel pump primes, but the gas is old, the jeep has sat for a year now. Even the master mechanic thinks it should get some fresher gas in there.

Know where I could find other ohm readings for other related sensors?

A factory service manual would help. I have the 95, which is essentially the same, and for a quick start (have to go out in a few min) I'll give you some ball park numbers.

Coolant temp sensor = under 1000 ohms at operating temp. About 18K ohms at 50 degrees. There's a chart for fiine checking, but that should do for good/bad test.

Same specs for manifold air temp sensor.

MAP sensor: test output at terminals A and B on sensor body. Ignition on, engine off, 4-5 volts. Should drop to 1.5 or so in neutral hot idle.

throttle position sensor - ignition on, engine off, backprobing at connector, output voltage at central terminal of connector should be greater than 200 millivolts at idle position, and under 4.8 volts at wide open throttle.

camshaft position sensor: Connect positive voltmeter probe to sensor output wire (cavity 1 on connector in a 95). Other lead to ground. Turn engine until rotor is at about 11 o'clock position, with pulse ring within the sensor pickup. Ignition on, you should get voltage of about 5 volts. Now while still observing meter, crank the engine, and voltmeter should fluctuate between 0 and 5.

Crank position sensor, with ohmmeter across B & C terminals, should give ohmmeter reading of open (no resistance) on the 1k to 10k scale.

Hope that helps a little. I'll check back in evening. Off to the malls (ugh) for the afternoon. Bah humbug!

I have the TSM and like a real fool, haven't spent much time in it. Thought it would be good for bolt and nut sizes. Need to dig into it.

Another post had the CPS getting checked on the A&C leads. MAP sensor had a good ohms reading.

Am researching parts cost to replace all and any sensors that involve starting. Would rather make sure that the existing TPS, and IAC are in good standing. Have read some on the IAC as an issue for while starting with an open throttle and having to keep foot on the pedal as a stuck IAC valve. Some believe this can be remedied by cleaning the valve.

My dad who is an old pro at doing this stuff is not around locally but believed from the onset that their was an Air/Fuel mixture mishap. Now should the CPS actually be fine, I have not a clue as to where to fix the mixture issue.

Test sensors, then replace if bad? Are there other adjustments around the throttle body that need attention at that point? Fuel injectors are cheap to replace, how can one tell if it is "flooded"?

As it stands, the Jeep will turn, but not fire. Last time (while dad was on the phone) It did start, temporarily, albeit with foot flooring the pedal, and would stall once foot was off to let idle.

So ready for this thing to run.

I still think that if you're getting spark with any consistency, you need not worry about the crank and cam position sensors, especially if you're not getting a code, and if it starts with ether or a snootful of gas.

Have you checked cranking vacuum? Make sure there isn't a manifold leak still lurking somewhere. Also I'd double check fuel supply. Check the fuel pressure again, and make sure it stays up. It might be intermittent, or a clog might have developed since you first tested it.

If the idle air controller is stuck or clotted with carbon, you should be able to take it out and clean it up. Be careful because it's delicate, but something that dissolves carbon should help.

You may also have to do some wiring harness troubleshooting. Make sure, for example, that the harness for the fuel injectors is good. Bad splices, though usually affecting only one injector at a time, can give you a tough diagnostic chase. Test continuity from the common 12 volt + source at the coil to each of the injector plugs. This system switches the ground side of the injectors, and puts +12 on all when ignition is on, using a series of branched splices in the harness.

Just for grins, open up the power distribution center where the relays are. You'll find a number of relays that are identical. Swap a few around and see if there's any change.

If you have the FSM, your tests and diagnoses will be split between section 14-35 (fuel system) and section 8-D (ignition).

Crank vacuum? I will indeed look this up.
No codes cause I have not used a diagnostics tool. I was looking it up today. Am not quite sure which tool will work best for a 93 Jeep Cherokee, from what I'm reading a OBD I is in the works since it is post 90' and pre 96' (obdII).

Question, will the diagnostics tool figure out where the problem is exactly (as I am almost sure nothing is an exact science with an XJ) but at least put me on the right path?

With OBDI, I don't think you get any more information from the diagnostic tool than you do from doing the diagnostics with the key.

In case you have missed this, on an OBDI Cherokee, you can get the diagnostic codes by cycling the ignition (just ignition, no start) on-off-on-off-on.....then wait and read the flashing of the check engine light. Each code will appear as two flashed digits. "12" will probably come up for a recent battery disconnection, and often appears whether or not it should. "55" is end of sequence, and always appears. Any other code is meaningful. If you have either a factory manual or a Haynes, it will list the codes. It's not that hard to get mixed up with reading the flashes, so run through a couple of times if you have anything unusual, to make sure you're counting them right.

The codes themselves may pinpoint a problem but if there's a wiring fault or something other than a direct failed sensor, it might only give you a general area to hunt in.

In my experience with the 93 and 95, any failure of the crank or cam position sensors, or anything else bad enough to kill the engine should set the check engine light, but it's always a good idea to check the stored codes anyway.

For vacuum, I'd just get a vacuum gauge, and plug it into the manifold port that goes to the vacuum reservoir and heater controls. Crank the engine and see if it develops something approaching the proper vacuum.

I may be wrong, but I suspect the problem is going to be something related to the fuel or the air, and not a sensor.