CPS Replaced, No Spark Still......

[McQue]

Grounding pin pin 5 should complete the circuit to energize the coil, close the contacts on the relay and pass power thru from pin 2 to pin 4 to the fuel pump.

 

[ihscoutlover]

Another update,

I did some steam cleaning of the caked on crud on the rear around the fuel pump and wiring, and I still have to check on a couple of things. I found now I get no red check engine light, and when I go to diagnostic mode, I get nothing. I have cleaned and prepped the ground for the PCM, which is now bare metal. No change. I have discharged the PCM and tried resetting it, and nothing. I am now wondering if the PCM is my culprit. I was planning on going to the JY and pull another one from a similar year XJ, since the FSM doesn't really hit on any way to truly test it for proper operation. I attached a 22guage wire to the battery negative, and it proceeded to heat the wire up and melt the wire's insulation. I will try and see if I run that wire to another source of ground and see if that doesn't do something different. I didn't seem to hear the relay energize, but I also tried several different relays and the effects were the same.

Should I try a "replacement" PCM and see if that does it, since that pretty much controls everything? All my relays are testing good per the FSM. I know it is expensive to just start throwing parts at it, but this seems to be getting a little rediculous. Everything I have been testing, seems to be testing correctly, but I can't test MAP, IAC, O2, and some of the other sensors, without getting the engine to operating temp. And since I can't even get spark out of it, its now got me starting to go bald with the hair I'm starting to rip out. Thoughts now??

Jeff

 

[Ecomike]

MAP, IAC, O2, have nothing to do with no spark or no fuel. And no spark and no fuel, pretty much is going to be a bad CPS, or bad wiring, like an ignition switch, or bad PCM. I would not replace the PCM until you find out what fried it, if it is the PCM?

Have you bothered to use a volt meter to check the CPS signal while cranking?

Also, no fuel at all sounds like no power to the fuel pump, even on the 2 second prime, which sounds like a PCM or ignition switch since you also have no spark.

 

[McQue]

Having a wire melt is a serious problem. Something is shorted. Find a buddy who is good with a meter take a look at the problem with you...just to double check everything you have already checked.

Another way to test your fuel pump would be to hot wire it direct to the battery just to see if it runs and pressurizes the fuel line.

 

[ihscoutlover]

Im gonna retest the CPS again, while cranking to see what I am getting. With the Check engine light not coming on when the key is turned on, I am led to believe that is the PCM that is out. Once I verify the CPS tomorrow, I will post up my findings. Keep some suggestions coming.

Mike in so far as the IAC, MAP and O2 sensors, I have had some others on here list those as causes of not starting. From what the FSM states, during the initial startup, Key on first(Open Loop)

PCM prepostions the IAC motor
PCM determines atmospheric pressure from MAP
PCM monitors engine coolant temp sensor input, and modifies fuel strategy based on this input.
Intake manifold air temperature sensor input is monitored
ASD Relay is energized by the PCM for approximately 3 seconds
Fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for 1 second unless the engine is operating, or the starter motor is engaged.
The O2 sensor heater element is energized through the fuel pump relay. The O2 sensor input is not being used by the PCM to calibrate the air-fuel ratio during this mode of operation.
The up-shift indicator light is illuminated(manual transmission only).

Engine Start-Up Mode This is an Open Loop Mode
The following actions occur when the starter motor is engaged:

PCM recieves inputs from:
Battery voltage
Engine Coolant Temperature Sensor
Crankshaft Position Sensor
Intake Manifold Air Temperature Sensor
MAP Sensor
Throttle Position Sensor
Starter Motor Relay
Camshaft Position Sensor Signal

PCM monitors CPS, if it doesn't receive a signal within 3 seconds of cranking the engine, it shuts down the fuel injection system.

Engine Warm-Up Mode This is an Open Loop Mode
During warm up, the PCM receives input from:
Battery Voltage
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Intake Manifold Air Temperature Sensor
MAP Sensor
Throttle Position Sensor
Camshaft Position Sensor signal
Park/Neutral Switch(Gear indicator signal)
Air Conditioning select signal(if equipped)
Air Conditioning request signal(if equipped)

Based on these inputs the following occurs:
voltage is applied to the fuel injectors with the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
The PCM adjusts the engine idle speed through the IAC and adjusts ignition timing.
The PCM operates the A/C compressor clutch through the clutch relay. This is done if A/C has been selected by the vehicle operator and requested by the A/C Thermostat.
If the vehicle has a manual transmission, the up-shift light is operated by the PCM.
When the engine has reached operating temperature, the PCM will begin monitoring O2 sensor input. The system will then leave the warm-up mode and go into closed-loop operation. Closed loop involves Idle Mode, and Cruise Mode.

This information is coming straight out of the FSM. This clarifies some of what has been explained to me, so if there can be some more clarification if I missed something, let me know.

Jeff

 

[ihscoutlover]

I will be attempting to wire the fuel pump direct to 12 volts to verify its operation tomorrow, when I work on some of the other items that need addressing.

McQue,

I had the relay plugged in when I did this, and I had the key in the on position to verify that the 12 volts was on where it was needed. That wire did get hot, and some of the insulation melted, but I should have probably used a little bit larger of a wire than that 22 or 24 gauge wire I had used. I am wondering, can I use a 14 or 16 guage and put it into place in the relay slot and see if I can get the pump to operate from there, where it is a bit closer to the battery, and thus I can do my thing straight from that spot rather than running a long lead to the rear for my power? Also I am going to see if I have a direct short at the pump, which could also be a problem. Just a thought there.

Jeff

 

[McQue]

It looks like that circuit is running on 14 guage wire... so you can try energizing the fule pump by pulling out the relay, and jump the relay pins 2 to 4 to put power onto the fuel pump.

 

[ihscoutlover]

Ok, I will try and find a 14 or 12 guage and see if I can hear the pump run. I know there isn't much fuel in the tank, as the low fuel light is one, and the tank shows at or near empty. I just don't want to put a whole lot of fuel in the tank to make sure if I have to pull the pump, I don't have to siphon a whole bunch of fuel and then I can make some things happen.

Jeff

 

[ihscoutlover]

I am trying to figure out where I read that the fuel pump if you run a continuity test on it would show bad, as to which connectors need to be checked. I will consult both my manuals for verification on this and report back my findings as well.

Jeff

 

[ihscoutlover]

I figured I'd post some pics up for those wanting to see just what I am working with/on:

The engine bay before I started to work on troubleshooting the no-start:

The rest of the Jeep, to include some interior shots:

And these to show no rocker rust:

Still not bad for a 155k Arkansas $375 Cherokee right?? I know its not the cat's meow, but it it what it is, and I feel that for even 1k by the time I get the issues worked out, it should be a fine running/driving rig. At least, if I still have any hair left. I have all the front end parts to fix the damaged ones, so the cosmetic issues are not but cosmetic for right now. The replacement front bumper also has the vacuum chamber thingy since the OE one was destroyed by the PO.

Jeff

 

[CJR]

Cool photos. A diamond in the rough!

Best regards,

CJR

 

[Matthew Currie]

It looks pretty solid. By the way, I don't know what differences are between a 94 and a 93, but I have a PCU from a 93 (4.0/aw4). I don't think there's any significant difference between years. I could part with that one for the cost of postage, if it's compatible.

 

[ihscoutlover]

Ok good news, the PCM might be ok. I reconnected the battery tonight, and jumpered the #2 and #4 pins on both the ASD, and the Fuel pump, with the fuel pump being tried first. It pressurized the rail, but then nothing. I tried the same with the ASD, and no change either. When I connected the battery and then turned the ignition switch on, low and behold the CEL was on. Upon seeing this, I took advantage of the moment to retrieve the codes. First code, was a 12, this means the battery has been disconnected within the last 50 key-on cycles. Next was a 54, this one is no Cam Sync Signal at the PCM. Likely culprit here is the Cam sensor, so I will look to replace that and see what's up then. The last one was a 42, this indicates an open or shorted condition detected in the Auto Shutdown Relay Circuit. This could be due to me still having my jumper wire in place there, instead of the relay. I will work to clear the codes and see if I get something else to show up. Then of course the standard 55 which is the completion of ETC display on the CEL. Thoughts here, besides the Cam sensor??

Jeff

 

[ihscoutlover]

Actually replace the pickup coil(which this one has just under the rotor and most of the parts stores have listed as the Cam Sensor), and since it appears to have some wear, might be what my hangup was. I will know when I get part in hand and see if I get some spark then. Thanks for the help, I think we are finally getting somewhere.

Jeff

 

[Matthew Currie]

Here's a trick for a bad cam sensor, if that's the problem. I've had this go bad on both a 93 and a 95, and this trick got me started both times. Turn on the ignition, and then unplug and replug the distributor with the ignition on. When you plug it back in, you'll hear some clicks, as if the system is booting up. You will then get one start. It won't restart again unless you repeat the process, and it probably will not run terribly well, since the fuel injection timing is scrambled. But it should start, and if it does, then you've got a positive diagnosis of a bad cam sensor.

By the way, it really is the cam position sensor. Although it lives inside the distributor, it's not really a part of the ignition. It times the fuel injection. A bad one will keep you from getting spark, but it appears that that's just because it stops the rest of the system from booting up, not because it has any ignition related function.

 

[ihscoutlover]

Matt,

I tried your trick. While I didn't get the clicking initially, I tried several other ways of doing the exact same procedure. The first time, it took almost a minute before it got both the ASD and FP relays to start clicking. They did that for a few seconds, and then stopped. However, I still am not getting any pressurization of the fuel rail. I then shut the ignition off, after no luck trying to start. I repeated the process again, and this time, when I hooked the battery back up, the ASD and FP relays began to click as I turned the ignition to the "on" position. Unplugged and replugged in the Cam sensor, and still nothing. One thing to note, I did have the cap and rotor off to clean them some to help with spark. I pulled the cam sensor out, and noted that there was some contact rubbing going on inside the distributor. The plate that the sensor rotates around, also showed some wear, and then I checked the rotor shaft. There is some play there and I am wondering if the distributor might be shot. I don't know if there should be much movement at all, and if so, there is a tad more than I would like. Thoughts and suggestions now??

Jeff

 

[Matthew Currie]

A little up and down play in the distributor is normal, but there shouldn't be any side play. However, I wouldn't have expected a little play to foul up the cam sensor that much.

Anyway, if you're not getting pressure to the fuel rail, I think your problem lies elsewhere.

By the way, have you gone through the wiring harnesses with an ohmmeter (forgive me if I've missed this, too lazy to reread the thread)? I'd be wondering a bit here if there's a bad wire or splice somewhere that's causing intermittent mayhem. It's a pain in the butt, but if you have the FSM, you should be able to trace the principal circuits from plug to plug, and see if there's something odd there. The FSM wiring diagrams are pretty unfriendly, and tracing a wire can involve jumping over numerous pages, but eventually you can usually find what you're after unless there's an error, which is not unheard of. (Don't trust the radio connection pinouts!)

If it stops snowing, I'll be heading out to the gym this morning, and try to get that PCU in the mail on the way home.

 

[ihscoutlover]

Matt

There is some side play. That's why I think its the cam sensor, since there is some wear marks on the sensor, as well as the ring it rides around.

Also , I reran the check engine codes, and now I am only getting the 12, and the 54. The other one has or is gone. I'll continue research on this one and figure out if it fixed itself, or temporarily went away.

As for the fuel issue, it pressurized up last night once, and hasn't since, and that was when I jumpered the wires from pin 2 to pin 4, but I never really heard the pump run. I need to hot wire it to 12 volts directly and see if it works that route, then I can see if there are some other wiring issues that I can address. I am suspecting a bad pump at this stage of the game, but I need to do a tad bit more troubleshooting to confirm that though. I'll keep you all posted.

Jeff

 

[Ecomike]

Sounds like you have verified the fuel pump is good. I would take a much closer look at that ASD relay wiring now!!!!!

You should be able to jump the ASD female pin contacts (relay output contacts) to see if it is an ASD wiring harness problem.

Be interesting to know if a dead Cam sensor can keep the fuel pump from running at all???? Does sound like it is time for a new (rebuilt) Dizzy to me.

I would still dig under the dash and check the wires to the ignition switch. The 87-90 Renix years are notorious for cooking some of those wires and the switch. Also the O2 sensor wires are bad about getting too close to the drive shaft and exh manifold, and shorting and burning up wiring harness wires in the process.

 

[ihscoutlover]

Mike,

Which contacts do I need to jump to see what is good or bad? Thanks for the advice. Im gonna keep trying. And yes the distributor needs to be changed, but I am also gonna have to look around and see what is up with why there is so much play in it. That and I have to make sure that I get it setup with #1 at TDC, and then I can pretty much drop the new one in, and fine tune it some.

Jeff