Replaced ECM computer box, won't start

[wretchy_gretchy]

I have a 1990 Ranger XLT 2.3L, I just replaced the original ECM with a re-manufactured one from an auto parts store. The truck was running (though terribly) before I removed the ECM.

I took the ECM out and cleaned it up a little bit, re-installed it to see if truck would run better, but it wouldn't even start. Today I installed a new one with the same exact numbers and still the truck would not start.

The starter will turn the engine, but there is no spark. Did I disconnect something else in the process?

The compartment where the ECM is looks moist. I think the heater core blew out with the previous owner, which cause the old ECM to malfunction.

Any ideas?

 

[RonD]

Well, an ECM controls everything by grounding, so all the grounds around/from the ECM must be bolted down, and make sure the ECM itself is bolted down.

That being said the 1990 should have the dual coil/dual spark plugs so no firing/spark would mean the the DIS(distributorless ignition system) module, usually mounted by the radiator, might not be getting power and/or a crank shaft turning trigger.
On the crankshaft behind the pulley is a sensor(CKP-crank position sensor), it reads when #1 piston is at TDC, this sensor getting a trigger from the crank turning "tells" the DIS module to turn on the spark, the ECM controls the spark advance and retard, but the DIS module is what makes the spark by grounding and ungrounding the coils.

Here is a diagram of an '89 system:
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Ignitionsystem_1989_2_3.JPG

The "ECA" is the ECM, lol

So I don't think messing with the ECM would have bothered the DIS module, it can function without the ECM, spark wouldn't advance so engine would run poorly but it would run.

 

[RonD]

As another thought, Rangers have 3 relays in a row, in the '90 they should be on the passenger fender well, or maybe under the Fuse box in engine compartment.
EEC relay
Fuel Pump relay
WOT relay(wide open throttle)

The EEC relay should close when key is turned on, this relay supplies power to the EEC(ECM), DIS module(spark), Fuel pump relay and injectors.

When key is first turned on you should hear the fuel pump come on for 2 seconds, if so then EEC relay is closing and at least part of the ECM is working as it is grounding the Fuel Pump relay to turn on the fuel pump.

If you don't hear the fuel pump start then check the EEC relay and its fuse

 

[wretchy_gretchy]

Thatnks for the replies, guys. It has confirmed my suspicion that it might be a grounding issue. When I pulled the box out originally, I noticed some corrosion where the box meets metal. I used a piece of steel wool to rub it away, but that kind of smeered the paint and probably just rubbed the corrosion in more.

Originally I dinked around with the fuse box thinking the computer was under it (I'm a dummy). I noticed there were only two relays under there and there was a slot for a thirds, but was obviously not included. The two relays are green and brown with matching plugs from the harness. I'll listen for the fuel pump next time.

Again, thanks for the replies. I'll report back with my finding when I have the time to work on it.

 

[RonD]

Green Relay is Fuel Pump
Brown is EEC relay

Both should click when key is turned ON
Green will click a second time about 2 seconds later when is turns OFF the fuel pumps

 

[wretchy_gretchy]

Okay. I got out there today and did some work, with no success. I cleaned and inspected all the areas around the ECM and checked all the grounding points. Everything looks fine.

When I turned the ignition, I did hear both the fuel pump and EEC relay click. But I'm not getting any spark to the plugs.

I'm hitting a wall. It seems like it should be so simple. Would I be able to test for codes from the new box using Ignition On Engine OFF? Or would it probably give me erroneous codes or not respond at all?

 

[zekew64]

I'd go out on a limb and see if your ignition module is bad. If you had issues with corrosion, and the module has never been replaced, could be that the module is also corroded. Just be warned that the heads for the bolts that are really tiny and prone to rounding. Use some Freeze-Loc first to break the bond of rust/corrosion before removal. If the module is isn't getting signal, check the CKP (Crankshaft Position Sensor) and make sure it is sending a signal. If the CKP isn't sending a signal, it's probably bad and needs replaced first. Also, as a precaution, you can use a multi-meter to check your coils as well. Too much resistance there, and the coils won't let the spark transfer through the wires to the plugs.

 

[wretchy_gretchy]

After some research I'm also coming up with the ICM being the problem. I will also look at the CKP too.

The coils were replaced just before I bought the truck. I do not believe they are the problem, but I haven't ruled it out.

 

[zekew64]

If you have a Haynes manual, and have access to a multimeter, you can check the resistance of both the primary and secondary coils. Basically, you'll have to pair up cylinders 1 & 4 and 2 & 3; testing the harness connection will be the primary coil, the spark plug wire connection will be the secondary coil.

The specs are the following:

Primary resistance: 0.3 to 1.0 ohms
Secondary resistance: 6.5 to 11.5 k-ohms