View Full Version : No Spark '90 4.0

06-18-2006, 09:31 PM
Hi, this is my first post. It's really great to be here in amongst
all this AMC knowledge! Some of you may know me from when I lived in Colorado, no I haven't dropped off the planet.

I have an 81 AMC Spirit with a Borg-Warner T5 that I removed the 4.2
from and installed a 4.0 from a 90 Cherokee. You can see pictures of
my project at http://www.picturetrail.com/bowlamc

The transplant went great until it was time to turn the key - the
starter runs but no spark to the distributor. :confused: Everything ran great
when it came out of the donor Jeep.

The national AMCRC convention in Baltimore is in 2 weeks and I'd really
like to be ready to take this car but I'm having a hard time figuring
out what's wrong.

I have wiring diagrams of both vehicles, but I'm still confused.
Here are some questions I have:

1. What do you think are the most likely causes of my problem (so I
can attack those first and waste less time)?
2. What connections on the cabin side of the bulkhead connector are
required to make the engine run?
3. What is the "B+ latch relay" that the wiring diagrams refer to so much?
4. Other Jeeps of this era I see (and even in the manual's drawings)
have different connectors between the engine harness and the
bulkhead harness. Do I have some kind of special requirements or was
this a running change?
5. Is the bulkhead harness even necessary?

Thank you in advance for your help. This is the first time I've ever
attempted something like this so please be patient with me, and
hopefully you can make it to Baltimore and see the finished project!

Richmond, VA

06-22-2006, 10:11 PM
let's see...you are trying to use the ignition from the 4.0 without the ECM from the donor car and without the wiring and modules/sensors that system used????correct???let me tell you how i put a chevy HEI from a 250 six into a 258(4.2)...switch distributor drive gear and oil pump drive from points-type(amc/delco-remy)distributor and re-wire from ign source with non resistance wire using GM coil(external-not in cap)and you will have non-computer HEI. i have never tried this on a 4.0 but the ignition on that engine is managed by the ECM so for the stock unit to work you MIGHT need all the other stuff too

06-23-2006, 09:30 AM
Thanks Jeff, but I do have the ECM and all the sensors of course.
Check out my photos.

The device on the distributor housing that reads shaft rotation is called the Sync Sensor, while the device on the bellhousing that reads flywheel rotation is called the Crankshaft Position Sensor (CPS). They both need to be functioning before the computer signal is sent from the ECU to the ICM.

It'd be nice if I could just open/close switches or increase impedance to make it work, but the ICM is looking for specific code from the ECU before it will pass voltage through the coil. The ECU won't send that code until it gets the right input from all the sensors, or at least enough of them to start in "open loop" mode.

Given that, any other thoughts?

06-24-2006, 09:56 AM
that is why i suggested the chevy HEI adaptation i did back in 87 on a 6cyl javelin.never had any problems with it and it only took a few minutes to switch the drive gear from the old amc (delco)distributor to the inline 6 chevy HEI.as for the 4.0 are you using the EFI system or an aftermarket 4bbl like offy or clifford.i personally would go with 450 cfm carb 4bbl holley that way you do not have those BUNDLES of wiring to contend with.the chevy distributor i used came from a 78 250 inline six chevy pickup,the swap was easy,it worked great and eveyone told me it was impossible

06-25-2006, 07:11 AM
Thanks but I'd prefer to just do it the way I'm going.

Multipoint fuel injection with computer control for performance and economy.

It's exactly as it was done in 4.0 Jeeps, and that's how I want it because that design has proven itself strong and dependable and, being an American Motors fan with an American Motors vehicle, I want it to have all American Motors components under the hood.

I believe in American Motors.

06-25-2006, 09:25 PM
An update on my transplanted 4.0:
It still won't start.
I have tinkered with the CPS:
and I believe I have everything connected properly (albeit a little
messy at the moment)
Still no spark.
I have checked every sensor per the tests in the book and continuity
between them and the computer.

Now the big show is less than a week away. AAAH!
Any help is very welcome. Very very welcome. Is there anybody here
around Richmond who might like to come take a look this week? Or any
suggestions on where I could take it?

Thank you again,

06-29-2006, 10:45 PM
Another update:

Put 12V directly to yellow wire (terminal A) on ICM. No spark.
Maybe this ICM is bad, but it did work when it came out.
I'll go get another one and try it.
There is 12V going to the ECU, red wire terminal B8.

Swapped relays around, still no fuel pump run - but if I put 12V directly to one of the wires in the relay recepticle (I forget which location) the fuel pump does run.

On a positive note, I did get my air cleaner adapter all finished up today. Check it out:


Will keep you posted on progress.


06-30-2006, 10:11 PM
It still doesn't start but I did make progress tonight - I now have spark at the spark plugs!
The difference? I made a little ground wire and connected the ECU housing to the neg. battery terminal.
This after I got wondering about it and found almost no continuity between them.
Also new - the B+ latch relay and idle speed motor both started working tonight!
The fuel pump still doesn't run, however when I take the F (orange/blk) wire off of the Start Relay and put it to the battery, the EGR solenoid clicks. I don't know WTF is going on there.

The car will not make it to this show, but I feel better that it is at least closer to starting now.

Next deadline is July 22 - All AMC Day at Cecil County Dragway. It WILL run and be all buttoned-up by then!

07-19-2006, 11:38 PM
Update: It runs!
What was my problem?
I had the distributor 180* off.
Thank you for suggesting it, I know there is somebody around here who admitted to having done that, now you have company!

My other problems such as fuel pump power went away once it ran.
Now my problem is, I can't get it to shut off!
I turn the key to ACC or OFF and it just keeps running.
I have the old start solenoid on the fender well, but it is really just acting as a terminal strip at the moment.

Here's a bad picture:
And a worse drawing:

I would think this is very similar to a Renix engine swap into any Jeep that originally had a 258 and a GM steering column.

Any advice on this or anything else that springs to mind at this point is welcome.
Thanks for all your help guys,