Intermittent Code 41 Gremlin

[JCTracker]

I had a code 41 error on one of my two 1990 Trackers. I used all of the info provided on the forum, FixKick pages, FSM and any other websites that covered the topic. Everything checked out. Distributor was good. Coil was Good. I had good spark. Noise suppressor tested fine. Passed all Go/No Go tests in the FSM but still no fuel to the injector. 

Next I started swapping parts from my known good Tracker to the one that wouldn't start. It wasn't until I put the known good ECM in the problem tracker that I could get it started. This suggested a bad ECM was the cause of the Code 41 but when I connected it to my running Tracker it fired right up.

Scratching my head I put the suspected bad ECM back in the tracker with the code 41 and it now fires up and runs with all of its original components reinstalled. I should be happy except the next morning I tried cranking it up and again no fuel to the injector and a code 41. I unplugged the ecm, plugged a bad one in, tried to start (but didn't), reconnected suspect ECM and it fires up again. 

If I didn't know any better I'd think the ECM was somehow holding the error code in memory but I swear the stupid thing has been unplugged and plugged back in a dozen times and battery was disconnected many times during the 3-4 day of troubleshooting. I know the ECM doesn't have an onboard battery that could save the code when disconnected from external power source and I'm pretty sure everything on the board is solid state so there aren't things like relays that might be sticking closed. 

So the question that bugging me is why it takes plugging a different ECM (good or bad) up to the vehicle to get the vehicle to get this particular ECM to forget about it's Error 41 Code. The other question is why does it come back? Is the ECM on the verge of failing or is there maybe something in the ignition system that has an intermittent issue that could also be on the verge of failing which causes it to run sometimes but occasionally fail? This would indicate the ECM is just doing what it's supposed to do but which ignition part is most likely to cause such a problem and, again, why does it take swapping ECMs to get the code to clear up? 

Thanks in advance for sharing any thoughts or insights
JC

Two 1990 Geo Trackers. Stock 4x4  MT. One works great, the other is being difficult

[Trk90]

Just curious… have you tried installing the suspect ecm in the “good tracker” to see if it starts hours, days, etc. later? Also, have you replaced the caps on the suspect ecm? I remember when my 1990 started running rough and eventually wouldn’t start, the mechanic said he could get it to run by literally banging on the ecm.

[JCTracker]

Just curious… have you tried installing the suspect ecm in the “good tracker” to see if it starts hours, days, etc. later? Also, have you replaced the caps on the suspect ecm? I remember when my 1990 started running rough and eventually wouldn’t start, the mechanic said he could get it to run by literally banging on the ecm.

Answer to question 1
Sorry but I'm not quite sure where you're heading with this train of thought but each time I've installed the suspect ECM in the good tracker it starts right up. I have only tried doing so when the problem presents itself in the other tracker though. 

Question 2..........
I haven't gone there yet but I know what you're getting at. This is all part of a project to get the new tracker running after it's been sitting for a several years.

 I'm basically building it to be a trail buggy for the spring. Spent the past 3 months working on suspension, brakes, rebuilding engine etc. Just got to the point where I could finally try to fire it up and the Code 41 presented itself. I'll probably get to a point where I'll replace the caps on the ECM just because I'm it's a prudent thing to do with parts that could be more than 3 decades old. 

Thanks for your reply
JC

[Trk90]

Just curious… have you tried installing the suspect ecm in the “good tracker” to see if it starts hours, days, etc. later? Also, have you replaced the caps on the suspect ecm? I remember when my 1990 started running rough and eventually wouldn’t start, the mechanic said he could get it to run by literally banging on the ecm.

Answer to question 1
Sorry but I'm not quite sure where you're heading with this train of thought but each time I've installed the suspect ECM in the good tracker it starts right up. I have only tried doing so when the problem presents itself in the other tracker though. 

Question 2..........
I haven't gone there yet but I know what you're getting at. This is all part of a project to get the new tracker running after it's been sitting for a several years.

 I'm basically building it to be a trail buggy for the spring. Spent the past 3 months working on suspension, brakes, rebuilding engine etc. Just got to the point where I could finally try to fire it up and the Code 41 presented itself. I'll probably get to a point where I'll replace the caps on the ECM just because I'm it's a prudent thing to do with parts that could be more than 3 decades old. 

Thanks for your reply
JC

What I was getting at is if you have the same problem with the flakey ecm in both vehicles IF it’s left overnight or longer. If it works properly in the good tracker you would think it has to be an electrical issue in the other.

[JCTracker]

@Trk90...........

Got it. Good point/suggestion. I'll keep it in mind if the problem persists.

Thanks
JC

[fixkick]

code 41 is ECU telling you the tachometer signal and the coil primary is dead. or weak or misfiring.
or bad wiring to the distributor.
yes the suppressor falling off will cause this. too.
a bad coil primary igniter too.
or bad spark coil, primary shorted.
yes old caps love to fail. they dry out inside and are bad, the one in the corner largest fail first
ok it is a 1990,
8valve engine.
when code 41 hits the ECU cuts spark so there can not be a fire. (crash and burn protection logic in the ECU)
so focus on spark only, ECU bad is last.
the 90 is not like the 91 at all.

the 90 has 2 things inside the that can fail
the VR sensor and the ignitor module inside. the VR has a gap spec too.
and the VR is known to fail or go intermittent or just the wires are bad.
its not the ECU its a bad dizzy or bad wires to it.
or the ground to it is bad.
schematic is here.

https://fixkick.com/INJECTORS/89/89-90schem1.jpg

good luck , I am kickfix.
the guts of VR are here
seen off here
https://fixkick.com/IGN_timing/89-timing.html

seen there id 6,7,8 are bad. or wires
the ECU is just saying the tacho single is dead or weak or intermittent.

[fixkick]

I bet the ECU did not lie to you.
bad wiring tops the list.
to dizzy
or inside it wires bad or the 2 electronic parts inside bad.
or fire wall and engine grounds are bad.