Engine cranks but doesnt start! No spark!

[FullBlownModz]

Hey forum! I recently developed a rod knock in my 4.0 91 Explorer motor and replaced it with a junkyard motor from a wrecked 4.0 94 Explorer. I kept the PCM from the 91 but used the wiring harness from the 94. After getting everything all hooked up I wasn't getting any fuel and realized that my fuel pump was bad and put on a new fuel filter and fuel pump but now I am not getting any spark. I get code 14 when i check the computer. I have replaced the relays, fuses, crankshaft sensor with the one from the running 91, spark plugs, wires, and coil pack and still cant find the issue. The only thing im weary of is the harness connector was a circle instead of a square so i spliced all the wires to make the new harness connectors fit. The wires were all matched, connected, and taped. Any ideas to why this thing wont start? Thanks in advance!

 

[Gadget X]

The 91 uses a "batch-fire" system, where the 94 uses a sequential fire system. If you use the 94 pcm, that may fix your problem. Good luck with it!

 

[alfilrey]

It will not work; it is advisable to reinstall the harness 91 to work with your pcm. Is different pcm settings. 1991-1992 models do not use the sensor position of the camshaft, at least not mine, from 93 and appears on engines which causes a change in the configuration of the PCM and therefore the wiring harness.

 

[FullBlownModz]

It will not work; it is advisable to reinstall the harness 91 to work with your pcm. Is different pcm settings. 1991-1992 models do not use the sensor position of the camshaft, at least not mine, from 93 and appears on engines which causes a change in the configuration of the PCM and therefore the wiring harness.

So you would recommend either putting in the old harness or a newer pcm?

 

[vq5speed]

When you put the 94 motor in you should of only needed to strip it down the to a long block. Put all your 91 stuff on to it. So your 91 wiring and connectors would all fit right back on. I did it with a 95 long block didn't swap anything else engine fired right up.

 

[FullBlownModz]

When you put the 94 motor in you should of only needed to strip it down the to a long block. Put all your 91 stuff on to it. So your 91 wiring and connectors would all fit right back on. I did it with a 95 long block didn't swap anything else engine fired right up.

Yeah i probably should have done that but i didnt realize there was a difference. I still have the old wiring harness but it is pretty messed up considering it was on a mud truck haha

 

[FullBlownModz]

So, i just put back on the old wiring harness and still no spark! It wouldnt even turn over by key so i had to jump the solenoid and still got nothing. Should i just go get pcm out of a junked 94 explorer and hook up the 94 wiring again?

 

[vq5speed]

Its not a PCM issue i'm pretty sure. The long block doesn't know what year truck its in if you put all the sensors and senders from the 91 onto the 94.

Do you hear the fuel pump prime up when you turn the key to ignition. Code 14 is Crankshaft sensor. I know you said you put one from a running motor but I would go buy a new one anyways since your getting that code. A bad crankshaft sensor would keep the motor from starting.

 

[FullBlownModz]

Its not a PCM issue i'm pretty sure. The long block doesn't know what year truck its in if you put all the sensors and senders from the 91 onto the 94.

Do you hear the fuel pump prime up when you turn the key to ignition. Code 14 is Crankshaft sensor. I know you said you put one from a running motor but I would go buy a new one anyways since your getting that code. A bad crankshaft sensor would keep the motor from starting.

Yeah it primes. I just put in a new pump. Ill go pick up a new sensor and a 91 wiring harness since the main connector is all spliced up now haha ill let yall know how it goes!

 

[Turdle]

How much of the "new 94" engine did you use? You really should use the 91 ecm,upper and lower intake, injectors, wiring and exhaust. Your 91 does not have the 2 oxygen sensors needed to use the 94 ecm.

 

[FullBlownModz]

How much of the "new 94" engine did you use? You really should use the 91 ecm,upper and lower intake, injectors, wiring and exhaust. Your 91 does not have the 2 oxygen sensors needed to use the 94 ecm.

I used the whole engine and just the main wiring harness that includes the injector, coil pack connector, cps, etc..

 

[FullBlownModz]

I picked up a 94 pcm and put back on the 94 wiring and im still getting no spark.. any suggestions?

 

[Turdle]

You added an 02 sensor?

did you connect the cam sensor?
Egr?

 

[FullBlownModz]

You added an 02 sensor?

did you connect the cam sensor?
Egr?

No 02 sensors are connected, not too sure of the cam sensor and egr but they should be connected

 

[Turdle]

Well, from what I remember from the 94 wiring is the crank sensor signal goes along with, and through the cam sensor signal.

You might check this. You'll also need an 02 sensor signal to run I think. 94 has 2 of them.

Seriously, I went through all of this on our 93. The previous owner had tried to eliminate the california (94 style) wiring using the california ECM, but it never ran quite right.
Thankfully, I had the time, and other members were more than helpful in getting it all back to the 93 style wiring it needed to run correctly. I still think you really need to change the 94 upper intake setup back to the 91 style and throw the 91 ecm and wiring back in for best results.

 

[FullBlownModz]

Okay so i put in the original 91 computer and got new wiring that isnt spliced from a 91 and im still not getting any spark. What am i doing wrong? Haha

 

[vq5speed]

Have you checked to see if you have spark from coil to plug wire. Pull a wire off the coil sit it a inch or so away see if a spark will jump across. Do this to each one.

 

[natenkiki2004]

For the 1991, it only uses the crank sensor as input to the ICM that controls spark. It's a very simple setup. Backprobe one of the yellow wires on the coil and watch for voltage while cranking. That will be your control for that coil. If you get absolutely nothing then the ICM isn't getting the info it needs or isn't being powered or is just faulty.

 

[FullBlownModz]

Have you checked to see if you have spark from coil to plug wire. Pull a wire off the coil sit it a inch or so away see if a spark will jump across. Do this to each one.

Ive already tried this at the coil and end of the plugs with no luck :/

 

[vq5speed]

So you had no spark from coil. So why not replace the coil