Jump to content

1986 Comanche No Start Condition


Recommended Posts

Let's keep this simple. 

 

TBI, ECU will prime fuel pump for 2-3 seconds when you turn the key to on or ignition. After it primes it will shut the pump off. 

 

ECU, when ECU senses that the engine is turning over, signal from CPS, it will run the pump and send a pulse signal to the injector and allow spark. 

 

CPS, if no signal to ECU, ECU will shut down pump and end pulse signal to injector and end spark. 

 

If your injector is not pulsating- no signal from CPS to ECU. Or you have a wiring issue or you have a bad ECU. 

 

 

It's that simple. 

 

What ECU did you get to replace the original and why did you replace it?

Link to comment
Share on other sites

Right now, I've got this Comanche that a man is trying to get running for his son as a first vehicle. He's in way over his head in the amount of money he's spent on this thing. In addition to that I've got a 99 Chevy Suburban with a 5.7L vortec that is pushing antifreeze into the crankcase and a 96 Ford explorer that is throwing O2 sensor codes after replacing the exhaust system and a 77 Jeep CJ7 complete rebuild project going on all at the same time! I'm stretched a little thin at the moment. 

Link to comment
Share on other sites

3 minutes ago, Jeep Driver said:

Let's keep this simple. 

 

TBI, ECU will prime fuel pump for 2-3 seconds when you turn the key to on or ignition. After it primes it will shut the pump off. 

 

ECU, when ECU senses that the engine is turning over, signal from CPS, it will run the pump and send a pulse signal to the injector and allow spark. 

 

CPS, if no signal to ECU, ECU will shut down pump and end pulse signal to injector and end spark. 

 

If your injector is not pulsating- no signal from CPS to ECU. Or you have a wiring issue or you have a bad ECU. 

 

 

It's that simple. 

 

What ECU did you get to replace the original and why did you replace it?

YES!!!! This is what I needed!!! Thank You!!! Ok... I think we can go from here. Jeep Driver, YOU ARE THE MAN!!!! CPS or wiring issues. Thank you! 

Link to comment
Share on other sites

13 minutes ago, Jeep Driver said:

Let's keep this simple. 

 

TBI, ECU will prime fuel pump for 2-3 seconds when you turn the key to on or ignition. After it primes it will shut the pump off. 

 

ECU, when ECU senses that the engine is turning over, signal from CPS, it will run the pump and send a pulse signal to the injector and allow spark. 

 

CPS, if no signal to ECU, ECU will shut down pump and end pulse signal to injector and end spark. 

 

If your injector is not pulsating- no signal from CPS to ECU. Or you have a wiring issue or you have a bad ECU. 

 

 

It's that simple. 

 

 

Well said.

Link to comment
Share on other sites

1 hour ago, wclegere said:

Engine has plenty of spark. Yes it will fire when gas is dumped into the TB but that really doesn't help much with the solution, does it? 

 

Of course it helps.

 

An internal combustion engine needs three things to start and run: fuel, air, and spark. If all you know is that it won't start, you don't know what to check first. If you can pour gas into the throttle body and it starts, that verifies that the ignition system isn't a problem. So you DON'T worry about CPS, ECM, coil, or distributor. Also, it's getting air so you don't worry about valves or camshaft.

 

So you're down to a fuel delivery problem. Focus your attention on troubleshooting the fuel system.

Link to comment
Share on other sites

  • 2 years later...
On 2/14/2019 at 9:09 PM, wclegere said:

YES!!!! This is what I needed!!! Thank You!!! Ok... I think we can go from here. Jeep Driver, YOU ARE THE MAN!!!! CPS or wiring issues. Thank you! 

 

Having the same issue with my 86 Comanche.  It will start and then die after two seconds.  Replaced the CPS, fuel pump, Map, relay.  Did the new ECU fix your issue? 

Link to comment
Share on other sites

40 minutes ago, Nick Walker said:

 

Having the same issue with my 86 Comanche.  It will start and then die after two seconds.  Replaced the CPS, fuel pump, Map, relay.  Did the new ECU fix your issue? 

 

wiring is a big issue with these old trucks.  :(  have you accomplished all of Cruiser's MJ tips?  should be like the first link in the link in my signature :L:  

 

you wouldn't happen to have this little guy somewhere in the engine bay, would you?  it's white-ish and like 3" long.  it wouldn't have been there from the factory, but could have been added later on. 

 

280978134.jpg

Link to comment
Share on other sites

8 minutes ago, Pete M said:

 

wiring is a big issue with these old trucks.  :(  have you accomplished all of Cruiser's MJ tips?  should be like the first link in the link in my signature :L:  

 

you wouldn't happen to have this little guy somewhere in the engine bay, would you?  it's white-ish and like 3" long.  it wouldn't have been there from the factory, but could have been added later on. 

 

280978134.jpg

 

From what I think I have read, the 2.5 doesn't have the resistor.

Link to comment
Share on other sites

I know.  86 shouldn't have it and the 2.5 shouldn't have it.  but dying repeatably after 2 seconds is exactly what a failed resistor would do so I figured I'd ask just in case a previous owner had it installed.  :L: 

 

what are you getting out of the CPS?  is that signal getting past the connector?  does the truck keep running if you put gas or starter fluid in the TB? 

Link to comment
Share on other sites

11 minutes ago, Pete M said:

I know.  86 shouldn't have it and the 2.5 shouldn't have it.  but dying repeatably after 2 seconds is exactly what a failed resistor would do so I figured I'd ask just in case a previous owner had it installed.  :L: 

 

what are you getting out of the CPS?  is that signal getting past the connector?  does the truck keep running if you put gas or starter fluid in the TB? 

 

What do you mean what am I getting out of the CPS?  Sorry I'm not the most mechanically inclined person but I am learning.  I can keep it running if i continuously apply the throttle but it runs very rough.  It will come close to stalling then I can get it to rev but will die if i do not keep in the throttle.  

Link to comment
Share on other sites

7 minutes ago, Nick Walker said:

 I can keep it running if i continuously apply the throttle but it runs very rough.  It will come close to stalling then I can get it to rev but will die if i do not keep in the throttle.  

 

that's a huge clue there.  that tells me the CPS is working and the computer is working. 

 

do you have a multimeter?

Link to comment
Share on other sites

7 minutes ago, Pete M said:

I know.  86 shouldn't have it and the 2.5 shouldn't have it.  but dying repeatably after 2 seconds is exactly what a failed resistor would do so I figured I'd ask just in case a previous owner had it installed.  :L: 

 

what are you getting out of the CPS?  is that signal getting past the connector?  does the truck keep running if you put gas or starter fluid in the TB? 

 

Yes i do. 

Link to comment
Share on other sites

41 minutes ago, Pete M said:

the link in my signature has threads on testing the various sensors.  I would test the TPS and idle controller.  :L: 


Oddly enough the TPS has never been plugged in to my Knowledge. The connector is melted and I think it was set manually to where the throttle is resting against the throttle. It had always ran fine so I never messed with it 

Link to comment
Share on other sites

1 minute ago, Pete M said:

um, what?  :thinking:  how can it run without the throttle position sensor plugged in? 

I mean it will run. The ECU has default readings to get the engine running but as soon as you throttle it the engine sputters and dies due to the demand and the ECU can’t compensate with no TPS. I’ve tried it before but Nick definitely does need it plugged in and adjusted per the factory specs. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...