check engine light came on and rpms dropped by half

[Kedyn's Crow]

I have a 1990 Ranger 4X4 with a 5 speed standard and when I was driving it today the check engine light came on and the rpms dropped by half. I didn't notice any major differences in how the truck ran and all the other guages were showing correct. When I got to work I shut the truck off and restarted it and the rpms were normal and the check engine light was not on. I haven't had a chance to pull codes on it yet. I have read it may be a bad DIS, is that the ignition control module that is on the intake that usually goes when this happens?

I just bought the truck last week and have only put about 150 miles on it so far.

Thanks.

 

[Sevensecondsuv]

I had this happen on mine. The tach read half what it should, the CEL was on, and the computer threw a code about not being able to control ignition timing. The issue on mine was that the driver's side ignition coil took a crap. The engine still ran perfectly fine because it was still firing on the passenger side plugs. Take the ignition coils off and take them to autozone and they will test them for you. The last time I bought an ignition coil it was about 40 bucks, not too bad.

I've never, in all my years owning and maintaining multiple fords, had a DIS module go bad, so I think it's highly unlikely.

Also look for bad wiring connecting all the ignition parts (crank trigger, DIS module, Coils). I once had a nicked coil control wire causing a nasty miss.

 

[Kedyn's Crow]

Thanks, I did some testing and when I pull a plug wire off on the exhaust side I have a lot of fire. I pulled a plug wire off the intake side coil and the truck wouldn't stay running so it looks like both the coils are good. I'm going to check for bad wires later when I have some time when it is light out to look at it better.

 

[Kedyn's Crow]

I was just able to pull codes and there were 2 the first one was 14 Ignition profile pickup (PIP) circuit failure and the other one was 24 Coil #1 primary circuit failure.

 

[Sevensecondsuv]

Thanks, I did some testing and when I pull a plug wire off on the exhaust side I have a lot of fire. I pulled a plug wire off the intake side coil and the truck wouldn't stay running so it looks like both the coils are good. I'm going to check for bad wires later when I have some time when it is light out to look at it better.

So if I'm reading this right, when you pulled off the plug wire on the exhaust side the engine ran fine, but when you pulled a plug wire off the intake side, the engine died?

If that's the case, it tells me your exhaust side ignition coil is dead.

Also, the exhaust side is the #1 side, so the code about "1# coil primary circuit failure" means that the exhaust side coil isn't working properly.

And you'll always get the PIP failure code when part of the ignition system isn't working properly.

My guess is that the exhaust side coil is shot or you have bad wiring somewhere. Like I said above, Autozone will test the coils for free, there's no reason not to take it in. Troubleshooting is easiest when you eliminate one possible cause at a time.

 

[Kedyn's Crow]

When I pulled the exhaust side plug wire off I pulled it off at the plug and I could see blue fire jumping and actually hear it jump so the coil is working. The truck sputtered but didn't quit running when I did this.

When I pulled the plug wire off on the intake side I pulled it off the coil because I couldn't get it off on the plug. When I did this the truck started but would not stay running so that means that coil is firing as well.

I moved some wires around and the problem hasn't come back up after driving 50 miles so it looks like it was a loose wire.

 

[Sevensecondsuv]

OK, I misunderstood you last time.

If it was a loose wire, I would figure out exactly which wire it was and fix it. But that's just me. I don't like vehicles dying in the middle of the road due to loose wires.

Glad you figured it out.

 

[Kedyn's Crow]

Thanks for all the help. I'm not partial to being stranded either.
The coil pack wasn't mounted and was just laying by the inner fender under the dipstick tube, I secured it and I it seems to be alright now. I'm going to check everything out better this weekend when I have some time wiht light to look a it.