86 MJ 2.5 TBI No Spark No Fuel

[dastrius]

Hey all! I recently acquired an 86 MJ TBI 2.5 and was told all it needed was a fuel pump. Upon further inspection it definitely needs more than a fuel pump.

 

It cranks but no spark and no voltage going to the fuel pump. We took a look at the signals coming into the ECU, and there are ignition signals coming in from the ignition itself, but no signals coming out to the ignition coil. My first check was the CPS, and it was reading .4 Volts, so I ended up replacing it. I work for O'Reilly so I went the easy route and picked up one from Standard. Now it reads .5 Volts, which sounds like it is where it needs to be, but I know there can be a bit of bias towards genuine mopar CPS's. So I have one from Crown on its way.

 

I tore apart the ECU and no obvious issues such as blow caps or corrosion, so I'm assuming the ECU to be alright.

 

Now the bigger issue I've noticed with this MJ is that there is quite a bit of rat damage. I completely removed the cab harness and repaired it to the best of my ability but I've yet to fully check the bay harness.

 

My main question I guess is, what signals/sensors do i need to communicate with the ECU to send spark and voltage to the fuel pump?

 

I have checked out Cruiser's Tips and I've refreshed the body ground and the dipstick grounds so far, and the fuel pump ground is the next on my list.

 

Any help is appreciated. :)

[eaglescout526]

7 minutes ago, dastrius said:

My first check was the CPS, and it was reading .4 Volts,

This is still acceptable. 
 

7 minutes ago, dastrius said:

My main question I guess is, what signals/sensors do i need to communicate with the ECU to send spark and voltage to the fuel pump?

 CPS does spark. 
ECU controls the fuel pump. Check the relay and make sure the relay is good and clean along with the block. 

[Yreka_Kid]

Hi All,  I'm trying to help OP get this thing going.  Its a bit of a mess so we are trying to work on one thing at a time.   I'll try and add a bit more information here: 

Right now, we are trying to start with/tackle the lack of spark but any other advice on methodology or otherwise is welcome...

- We have been doing quite a bit of searching/reading & have gathered the ECM itself is rarely the problem - trying to isolate as much as possible & eliminate all of the other possibilities before pulling the trigger trying to find another one.   

*Assumption based on research* - if we have 12VDC on the appropriate inputs, proper ground(s), and an appropriate ESS Signal at the ECU, we should see an output (ground?) from Pin27 (Orange black) at the diag con 1 and ICM -- I believe we have this, and yet we aren't seeing anything output.  

Here is what we have looked at/done so far.   

Starter cranks engine over fine - All of the fusible links off of the starter relay appear to be OK.  

We've done the "must do" from Cruiser 54 page (1-5) we saw mentioned quite a bit on all of the older problem threads - This truck being an 86 doesn't have the C101 so we did the connector behind the fuse box instead as it had plenty of the black tar stuff.   


Checking @ ECM connector
Grounds @ pin 1 and 2 (Black) ECU OK continuity - I can't remember if we checked Resistance, but can double check  
The latch relay is never being triggered by the ECU so we've bypassed that to get 12V on Pin 19 (pink wire) -- ( I assume you should see a ground output on Pin 7 from the ECU to trigger this when the key is on and shortly after off?  Its open all the time) 
12VDC on Pin 4 (red) constant 
12VDC on Pin 3 only with key on (Yellow) 
Truck is an MT so we have been ignoring Pin 12 (BlkWht) which I believe would prevent the truck from being started unless in Park or Neutral but maybe we need to verify ground here?  Not sure if its relevant on the MT since the drawing lists A/T 
~0.4 to 0.5VAC across Pin 11 (Vio/WHT) and 28 (WHT BLK)  while cranking  - this is a new sensor, the original was marginal @ about .3 so we replaced that.  

Removed cover to the ECM - caps etc look good - no corrosion on the connectors.  

Initially we were testing with a spark checker off the coil, but have since moved onto looking for a signal going into the coil/ICM which is not there.  


 

[Yreka_Kid]

It was the ECM - Issue solved 

 
 

[eaglescout526]

3 hours ago, Yreka_Kid said:

It was the ECM - Issue solved 

 
 

Thats scary that the ECU failed.