Hi all, I have a 1991 4.0 cherokee laredo, orginal engine was in bad shape so I took it out and rebuilt it. Now the engine will just crank all day but not fire. Sometimes I get a pop out of it when I first start to crank it. It is setting a code 42 for ASD relay circuit only I can't find a fault in the relay or in the circuit. I have tried all I can think of to find a solution but have come up empty so far. Need some help from someone with more experience in the normal voltage readings and operation of the electrical systems on the vehicle. It is all stock aside from I removed the a/c, the cruise, and added an adjustable fan controller to the electric fan, the ecu now doesn't control it.
When I test the sync sensor and the crank sensor with a scope I see a good pattern at the ecm connector. One thing that I didn't know is the wiring diagram says it's a 8v refrence. I see the ecm is sending a 8v signal out to the sensors. But the signal the sensor are sending back are only 5v... is that a normal reading, the ground wires show about 180mv while cranking, which is probably normal for a cranking condition? I show a start signal on terminal 8 at the ecu... with a test light. Tested primary and secondary resistance of the ignition coil which was normal. Checked resistance through all the injectors which were normal. There is fuel flow, I disconnected the lines off the rail and cranked it, did not check the actual pressure. The shut down relay shows 12v at terminal 30 and cranking voltage while cranking, same with terminal 86. Weird thing is the ecu terminal 57 always shows battery voltage even with key off. Tried an ecu from a 1992 automatic and had the same result? Thanks for any assistance. At this time I'm baffled...

 

1. Check for voltage at pin #87 of the Automatic Shut Down (ASD) relay, this circuit should only have voltage with the ASD relay installed and the vehicle running. With the ASD relay removed, a ground should be seen through the O2 sensor heater.

2. Try unplugging the alternator to see if it's back-feeding the system, next check the wiring harness on the Dark Green/Orange wire for shorts to power. Also check for internal shorts in the Power Distribution Center (PDC).

 

no pinched wires between motor and bell housing ?

 

How are you testing for a fault in the ASD relay and circuit? If I remember right you only have about 3 seconds from the time you turn the key until the PCM de-energizes the ASD if it does not get the correct input signals from other sources

 

While you are at it....check these as well.....
1. Check for B+ on pin 3 and 9 at the Powertrain Control Module (PCM).

2. Check for a good ground on pins 11 and 12 at the PCM.

3. Check for 5 volts on pin 6 at the PCM.

4. Check for 8-9.5 volts on pin 7 of the PCM.

 

I did try unplugging the alternator, which did not change the condition. I will check the 5v ref circuit. The 8v ref circuit pin 7 is good. I was assuming on the power and grounds at the ecu because my scan tool will communicate but I will double check. I show 12v at terminal 57 of the ecu while cranking, but have not checked at pin 87 out of the relay. Funny thing is I command the ASD relay to click through the ecu driver in the scan tool test, at leat I could before I will double check. No pinched wires as I can tell. and I ran lots of redundent engine and chassis grounds.

 

all fuses in pdc good power in and out second one from front 30 amp esp ?

 

I did check the fuses... but I will double check. I just verified that I can signal the ASD relay on through the scan tool which uses the ecu driver. I verified the 5v ref out of the ecu is present. Ohm checked the ground from the ecu terminals 11, 12, 5 they checked no resistance. Verified battery voltage into the ecu terminals 9 & 3. so terminal 57 at the ecu ASD sense input shows 7v key on and 10.5v cranking (cranking voltage). Terminal 51 at the scu ASD coil control shows 12v key on and 10.5v cranking... terminal 87 at the ASD relay shows 7 volts key on and 10.5 volts cranking. When you say a ground should be seen through the O2 sensor, you mean at the ecm? What I was wondering before is if I really don't have a ASD problem but the ecm is disabling it because of something else and just posting that code. When you get the cam and crank sensor on the pulse in an 8v ref circuit should you see 8v back to the ecu, because mine is showing only 5v?

 

Just a thought..Is it possible to bypass the ASD relay? Not forever but long enough to make something happen?

 

That I don't know... Thought about it, like maybe I can hard wire a switch or something. I'm not 100% sure but I kinda think the ecu may disable the coil and the injectors if it can't control the ASD relay...

 

you state getting pop when first cranking check spark injector noid and fuel pressure are all present during long cranking cycle ? dist not sink correctly ?

 

So I've been busy and the jeep has just been resting in the garage. Was thinking about the issue some and I was wondering if the crank and the cam sync are in harmony. I took the dist cap off and pulled #3 plug and I was feeling the compression out of the spark plug hole. I was using the #3 cylinder because I can see the dist sync sensor pass into the window. It looked like the dist was 180 off. I was not using a compression guage but feeling with my finger and I think I was getting a huff out of the cylinder with the rotor pointing to about the 2 to 3 oclock position. When I put the dist in I put it in pointing at the 4 oclock position with #1 at top dead on what I thought was compression stroke. I think I put the cam in incorrectly. I was wondering if any one knows where the proper index marks for the cam and the crank position are? Of if I can just pull the distributor and put it in rotated 180? I bought a cloyes timing set and placed the dot on the cam gear towards the dot on the crank gear... has anybody else run into a similar timing issue using this gear set? Thanks

 

timing marks are correct in picture you then rotated motor to tdc compression stroke no1 cyl then inserted dist correct ?

 

Ya I was pretty sure I did! But now I've had the dist out many times and rotated the engine so much I gotta recheck it. I can't remember the brand of camshaft. Maybe the dowel was indexed wrong. I've done many engines and never ran into a problem like this... It kinda appeared to me like the compression stoke was 180 off when turning by hand with the plug out. Don't have a guage at home to really check it...

 

as long as timing chain gears installed correctly, turn to tdc on compression no 1 index dist and drop it in