ECU - Manual vs. Auto

[aerocorey]

I missed the low pressure at the rail. You're right, that's different. As for mine...it was the CPS signal, not a starter or a cable or a relay. Roll start worked.

[jpnjim]

Aaron,

Wow, I saw you had posted this in a couple places,

I figured it would be solved before I could finish typing up a long winded run-on response, so I didn't jump in. ;)

 

I thought the other post said it was starting, then shutting off (tho I didn't read the thread, just the scroll over text).

 

 

 

 

Sounds to me after reading this thread:

 

you get in the Jeep, turn the key & it does not pressurize the rail, but it does crank the starter?

 

What if you just turn the key into the 'run' position, but not all the way to the start position?

 

Going to 'Start' & pressurizing the rail is pretty much step one of starting,

So that's the best place to start tracing out the problem.

 

 

 

 

So:

Key in RUN position (not start):

 

 

Do you hear the fuel pump click, and begin to pump up?

 

yes ----> check pressure at the rail

no -----> verify connections at fuel pump relay

 

Since it's a Comanche verify the Black in the harness to the fuelpump/tailights is grounded.

 

Lots of times you lose this ground connection, and the tailights being plugged in are the only thing supplying the ground to the harness & fuel pump (which is why you get the dreaded "MJ no start" when you remove the bed, or unplug the tailights.)

 

The fuel pump will not run for long in the 'run' position like this, it's just a quick 'whirrrrrlllllll', then it shuts off (I'm thinking the ECU shuts it down when it doesn't sense the engine spinning (running)).

 

In the 'run' position, the fuel pump is also dependent upon the ballast resistor, so that's another link in the chain to trace out if it's the fuel pump is not running in this mode.

 

 

 

The other mode that the fuel pump runs in is the 'Start' mode.

I had the my fuel pump stop working in the 'Run' mode at one point (in an MJ), but it would still work in 'Start' mode,

so I drove home with the key turned into the 'Start' position.

 

Easy to do, you just have to disconnect the starter control wire (to the starter mounted relay) after it starts,

while someone else keeps the key forward (in 'Start'). <-- so it starts, but then the starter doesn't keep spinning the whole way home.

 

So, the next step after testing your fuel pump in the 'Run' mode could be to test in the 'Start' mode.

 

You could disconnect your starter (like above) to test it (so you can hear the fuel pump), or just have a second person listen for at the tank the fuel pump while you crank the engine.

 

 

 

 

 

Or, you could just skip to the third way to test the fuel pump:

 

The last ditch method to test the fuel pump is to just apply 12v (+) directly to the ballast resistor.

It doesn't matter what side of the resistor you connect the 12v + jumper wire, but if the ballast resistor is bad, the fuel pump would only spin when connected to the 'load' (fuel pump) side.

('line' side wouldn't fire the fuel pump if the resistor is bad = this method can also be used as a way to test the ballast resistor).

 

If connecting 12v (+) to either side of the ballast resistor gets the fuel pump to spin (and it was not spinning for test #1, or test #2 above)

atleast you know the circuit beyond the ballast resistor is intact & working

 

You can backtrack, and keep your testing to the ECU, and underhood/under dash connections.

 

If connecting 12v (+) to the BR does not get the fuel pump spinning (and keep spinning for as long as you apply 12v + there),

either:

 

1) that black wire to the fuel pump is not connected to ground

2) that black ground wire is not completing it's path from ground, to the fuel pump

3) the (I forget what color) + wire from the ballast resistor is not completing it's path to the fuel pump

4) or the fuel pump is bad.

 

If this gets the fuel pump fired up, you should test the fuel pressure at the rail.

 

BE CAREFUL HERE.

 

Connecting that jumper to the ballast resistor makes a SPARK (usually a nice fat spark),

and testing the fuel pressure at the rail usually = GAS.

 

Spark + Gas isa fast way to wreck your Jeep/Garage/House (= bad :D )

 

Atleast keep a fire extinguisher around, another set of eyes/hands is even more helpful.

 

 

 

Hopefully after the above, either your fuel pump is working, or you've narrowed it down a little.

 

I haven't had as much luck tracing down ignition issues in these (haven't really had any to trace),

but I have the factory Renix fuel injection manual that I could go through to try to help figure this out beyond this.

 

Post up what you find, and we'll keep going.

 

Since you replaced the harnesses in this Jeep, and seem to have double checked most of the sensors & the ECU already, I'm leaning towards the problem being either a wiring connection, or the 'new' harness is damaged in some way.

[LoTGoD]

Sorry that I didn't jump back in here over the weekend.

 

Jeep club Christmas party + beer = me laying around the house all day yesterday!

 

 

The fuel pump kicks on and sends fuel to the rail. I have verified fuel pressure at the rail valve. The problem is that the injectors are not pulsing to spray fuel to the cylinders. I've pulled a few of the injectors, and they function as they should when I apply 12v of power.

 

I've taken about 10 days off from this thing, as the frustration level was just getting too high for me.

 

I plan to start back up tonight and change a few things out. I'll post up more later this evening, or tomorrow.

[jpnjim]

I'll try to pull out the 4.0L (Renix) FI manual later tonight (have to go out to do a side job right now :ack: ),

I'll also try to read some of your other threads, and see what else I missed.

 

So you have:

a Renix 4.0L engine, with a Renix flywheel, Renix distributor (that has not been pulled out), all renix sensors (some replaced/tested/etc), a replacement renix harness, and a tested working Renix ECU.

 

I also think I read you replaced the steering column.

 

That's alot of connections to make sure are still good, but since you're not getting both the fuel injectors, and the ignition, without looking at the book, I'd lean towards it being a wiring issue.

If you had not replaced the harness (or if you had not tested the ECU), I'd lean towards it being either the ECU, or something that needs to function before either ignition, or injection would be initiated (CPS {that you tested, and replaced a couple times}, or the sync sensor in the distributor {that you tested}).

 

Specifically, what did you change/replace since the last time it ran?

 

> Engine Harness

> CPU harness

> Interior Harness

 

Then you swapped the CPS (how did you melt that with the header?, do you mean you melted the harness, or the sensor itself?),

 

and tested:

the Ign coil

Starter Solenoid

Sync Signal

Fuel Pump

O2 (should start w/o this anyway)

ECU & Engine harness also tested.

 

This is starting to push me towards the steering column & interior harness.

 

I'll pull out the book, and see what that says.

[LoTGoD]

I'll try to pull out the 4.0L (Renix) FI manual later tonight (have to go out to do a side job right now :ack: ),

I'll also try to read some of your other threads, and see what else I missed.

 

So you have:

a Renix 4.0L engine, with a Renix flywheel, Renix distributor (that has not been pulled out), all renix sensors (some replaced/tested/etc), a replacement renix harness, and a tested working Renix ECU.

 

Renix 4.0 - Yes

Renix flywheel - yes (looked at the HO flywheel and determined it was an HO flywheel from Eagle's description)

Renix Distributor - Yes, never changed by me

Renix Sensors - yes, no swaps to anything newer; tested and tested again

Replacement Harness from an 89 MJ

ECU - Tested in friends 87 and it fired his up

 

I also think I read you replaced the steering column.

 

Nope, didn't figure it needed that just yet.

 

That's alot of connections to make sure are still good, but since you're not getting both the fuel injectors, and the ignition, without looking at the book, I'd lean towards it being a wiring issue.

 

I agree, that's why I'm so stumped. I've checked, and checked everything again, and then I checked it again!

 

If you had not replaced the harness (or if you had not tested the ECU), I'd lean towards it being either the ECU, or something that needs to function before either ignition, or injection would be initiated (CPS {that you tested, and replaced a couple times}, or the sync sensor in the distributor {that you tested}).

 

Specifically, what did you change/replace since the last time it ran?

 

> Engine Harness

> CPU harness

> Interior Harness

Correct on all these...and I'll one up you by saying that I re-installed all original harnesses that had worked before (unreliably, but it still started every time)

 

Then you swapped the CPS (how did you melt that with the header?, do you mean you melted the harness, or the sensor itself?),

The wiring on the old one was partially melted due to contact with the header. I've routed the new one so that can't happen now.

 

and tested:

the Ign coil

Starter Solenoid

Sync Signal

Fuel Pump

O2 (should start w/o this anyway)

ECU & Engine harness also tested.

 

Yes to all of these except the O2 sensor. Nothing I've read points me to no start, as you have also suggested

 

This is starting to push me towards the steering column & interior harness.

 

I'll pull out the book, and see what that says.

 

That's the only thing I have left to assume as well.

 

There may possibly be a Wildman sighting in my neck of the woods this week, depending on his travel schedule from Virgina.

 

I'm taking the night off once more, but plan to hit it hard again tomorrow.

 

I appreciate your help Jim (as well as everyone else that has contributed) and can't wait to get this sucker running!

 

Aaron

[500 MJ]

I'd be interested to see if your problems are caused by the Ignition control module. That darned thing had me chasing my tail for months on my white '90. Just over a 100,000 miles on the truck and for some reason it went on me.

 

The problems I had was intermittent. After we pulled the junk one out and replaced it we saw that the junk one actually overheated and so the contacts would make sometime and other times they wouldn't.

 

I went through a whole plethora of parts and sensors trying to chase it down. I'm too lazy to retype it so I'll just give you a link. Maybe it helps give you some direction towards getting yours back up and running.

 

viewtopic.php?f=2&t=13850&start=15

[Wildman]

Yes, some of us have been typing out ideas for what.........2 weeks now :hmm:

 

I missed the boat on the "no fuel in the rail" part :oops:

 

So......your getting fuel, just no spark, and Yes, I'll agree, you will not get the injectors to pulse with out a spark, the ECU will control that.

 

$500MJ make a good point about the ignition module........That's about the only thing you'd haven't changed out.......correct, and the CamPS.

 

You have or have not, changed the wiring harness back to the old one???

 

As I sent you the PM........I'll try to make it over for that stake dinner.......ah, er.....stop by on my way back, to give you a hand, and I'll bring all my books along :D

 

OH, and some spare parts.

[JeepcoMJ]

Aaron, if you have any issues while you're working on it you can call me tomorrow night. I'll pm my phone number again in case I didn't already.

 

 

 

I know for fact that that dash harness was good, and that it's interchangeable between years..I took it from that 89 5 speed and ran it in my 87 for awhile before I swapped to high output....and the reason for the H.O. swap was a utterly destroyed block on the renix motor.

 

If you're still having issues with this by the end of the week, I could dig up another 89 dash harness I have, and I have an 89 auto engine bay harness and just send them you're way for spares just in case.

 

-Pat

[jpnjim]

I'll pull out the book, and see what that says.

 

Bedtime now,

but I scanned some pics from the book that tells you what sensors the ECU is looking for in which mode of operation,

and what it does with them.

The form is pretty simplistic, but it does explain what's happening.

I'll try to post more here tomorrow.

[Wildman]

:eek: So.......alot goes on when you turn the key :eek:

 

Thanks for the info........I know down the road, I'll reference this :thumbsup:

 

We'll see how Lotgod makes out over the next couple days.

 

And........see, if I can make a 'house' call :D

 

It's so much easier to see, and hear something in person, than just seeing a screen and typing :roll:

[LoTGoD]

I'd be interested to see if your problems are caused by the Ignition control module. That darned thing had me chasing my tail for months on my white '90. Just over a 100,000 miles on the truck and for some reason it went on me.

 

The problems I had was intermittent. After we pulled the junk one out and replaced it we saw that the junk one actually overheated and so the contacts would make sometime and other times they wouldn't.

 

I went through a whole plethora of parts and sensors trying to chase it down. I'm too lazy to retype it so I'll just give you a link. Maybe it helps give you some direction towards getting yours back up and running.

 

http://www.comancheclub.com/forums/view ... 0&start=15

 

Just read your post. Seems like a viable option for me at this point. Do you happen to have a part number? I'll assume this is a dealer only item? I can't seem to find it online at my local places (NAPA, Advance, etc.) Maybe I'm searching for the wrong thing?

[LoTGoD]

Yes, some of us have been typing out ideas for what.........2 weeks now :hmm:

 

I missed the boat on the "no fuel in the rail" part :oops:

 

So......your getting fuel, just no spark, and Yes, I'll agree, you will not get the injectors to pulse with out a spark, the ECU will control that.

 

$500MJ make a good point about the ignition module........That's about the only thing you'd haven't changed out.......correct, and the CamPS.

 

Correct...both are still the same ones that came with the truck

 

You have or have not, changed the wiring harness back to the old one???

 

The current harnesses that are in the truck are all of the ones that PAt sent me from his 89 parts truck.

 

As I sent you the PM........I'll try to make it over for that stake dinner.......ah, er.....stop by on my way back, to give you a hand, and I'll bring all my books along :D

 

OH, and some spare parts.

 

Steak, lobster, pizza, ribs, you name it, I'll have it ready for dinner the night you are here, even if we don't fix it!

[LoTGoD]

I'll pull out the book, and see what that says.

 

Bedtime now,

but I scanned some pics from the book that tells you what sensors the ECU is looking for in which mode of operation,

and what it does with them.

The form is pretty simplistic, but it does explain what's happening.

I'll try to post more here tomorrow.

 

Thanks for those Jim. I've been using them since I downloaded that Renix Fuel Injection manual from Pirate last week or so.

 

I still appreciate it very much!

[LoTGoD]

:eek: So.......alot goes on when you turn the key :eek:

 

Thanks for the info........I know down the road, I'll reference this :thumbsup:

 

We'll see how Lotgod makes out over the next couple days.

 

And........see, if I can make a 'house' call :D

 

It's so much easier to see, and hear something in person, than just seeing a screen and typing :roll:

 

No doubt it will be easier to see what's going on in person, but I totally understand if it just isn't in the cards for you.

 

Either way, I'll be doing some work this evening, and I will post my results here, and possibly give you a call and let you know what I found out.

[500 MJ]

I'd be interested to see if your problems are caused by the Ignition control module. That darned thing had me chasing my tail for months on my white '90. Just over a 100,000 miles on the truck and for some reason it went on me.

 

The problems I had was intermittent. After we pulled the junk one out and replaced it we saw that the junk one actually overheated and so the contacts would make sometime and other times they wouldn't.

 

I went through a whole plethora of parts and sensors trying to chase it down. I'm too lazy to retype it so I'll just give you a link. Maybe it helps give you some direction towards getting yours back up and running.

 

viewtopic.php?f=2&t=13850&start=15

 

Just read your post. Seems like a viable option for me at this point. Do you happen to have a part number? I'll assume this is a dealer only item? I can't seem to find it online at my local places (NAPA, Advance, etc.) Maybe I'm searching for the wrong thing?

 

Now I've got a spare Chrysler one in my box of spare sensors & stuff, I can check for part numbers on that when I get home tonight.

 

Its not a dealer only thing. Rockauto.com has it: http://www.rockauto.com/catalog/x,carco ... ttype,7172

 

[LoTGoD]

Hmmm...I've already pulled that out and tested it in another MJ. His fired up about 10 times in a row with mine in it. His had no effect in mine.

 

I thought you were referring to the porcelain connector on the steering column. I guess that is the ignition switch?

[JeepcoMJ]

is the plug for the coil plugged in @ the right spot? there are two different spots it could plug in @ on the coil...only one is correct...

[500 MJ]

Well, I guess it was worth a shot, thats all I've got for ya...

 

For future reference I looked up the part # I have on my spare one.

 

Bendix # S100620004C "Made in France" :rotfl2:

 

' luck to ya - Brent

[LoTGoD]

Thanks Brent!

 

So...installed new battery cables tonight, and also swapped red tops between the TJ and the MJ. Still no start :(

 

A few pics of things that I might still be confused about

 

What is this connector that comes out of the steering column? The horn works, so I know it isn't that.

 

 

 

 

Also, as most of you know, the steering column is out of an auto. I have posted this question before, but I am hoping pics will help with an explanation. On the back of the ignition switch, it is open, with a pin that appears to be pushed inwards during the start sequence. Could this possibly be causing any issues?

 

 

 

Sorry for the crappy cell phone pics...the good camera is at work.

 

Again, thanks for all the help!

[JeepcoMJ]

that light switch is probably not the issue.

 

 

that connector is for cruise control..

[LoTGoD]

that light switch is probably not the issue.

 

The third and fourth pics are not the hi-beam switch, they are the ignition switch. This is where the rod comes from the key down the column to engage the starter and send 12v out to where it needs to be.

[JeepcoMJ]

that light switch is probably not the issue.

 

The third and fourth pics are not the hi-beam switch, they are the ignition switch. This is where the rod comes from the key down the column to engage the starter and send 12v out to where it needs to be.

 

I didn't look close enough.

 

I don't think that that nob connects to anything. if you have a spare, swap it out.

 

if not, I'll ship one out to you on friday. you *should* have a spare coil that came with the harness as well.

 

 

did you try swapping the connectors around on the coil?

[LoTGoD]

I didn't look close enough.

 

I don't think that that nob connects to anything. if you have a spare, swap it out. if not, I'll ship one out to you on friday.

 

No spare. Might buy a new one if I can find one. Don't worry about sending one out, I'll find one locally this weekend if I think i need it.

 

you *should* have a spare coil that came with the harness as well.

 

 

did you try swapping the connectors around on the coil?

 

 

I don't think there is one in the box. I'll have to check tomorrow.

[maddzz1]

If you think it will help, I can mail my 89 electrical manual to you to use. I know there are copies online but having the book at the truck may make life easier. Just send it back when your done. I also have the regular 89 FSM too if that will help.

[LoTGoD]

If you think it will help, I can mail my 89 electrical manual to you to use. I know there are copies online but having the book at the truck may make life easier. Just send it back when your done. I also have the regular 89 FSM too if that will help.

 

Jim,

Thanks for the offer, but I already have both of those printed out. They are helping quite a bit!

 

Thanks,

Aaron