Intermittent starting issues

[bossbob]

So, we've had this truck for about a year now, when I first got it it would quit running whenever it decided to, then no run at all. I replaced the ECM and it has been running great for about 6 months. Now we're kind of right back there. It will usually start when cold, run a few minutes or maybe a few miles then quit running again and won't restart. Spray starting fluid in it and it may or may not start. It has a full tank of gas, plenty of fuel pressure, and a 2nd ECM replaced last week thinking it might be the culprit again.

No change in performance, so where do I look next. When it does start it runs great, it just wants to shut down unexpectedly, almost like something is getting hot or something.

What do you guys think I should look into.

It's a 86 2.9 5 spd. Are there some electrical gremlins I need to look into.

Thanks again,

 

[RonD]

Common issue was TFI module on the side of the distributor, would quit or cause rough running when it warmed up

TFI info here: http://www.therangerstation.com/how...iv-electronic-engine-control-troubleshooting/

 

[bossbob]

Just brought it home on a tow truck, wouldn't start a couple hours ago. Now it fires right up and runs great??????

This is my kids truck, he doesn't tell me anything unless it doesn't run. Get in it and can't figure why the dash lights are on, apparently the brake lights don't work but when you press the brake pedal the dash lights come on......

 

[RonD]

Yes, intermittent is a pain

If you get a spray can of Quick Start(ether) you can do a 50/50 test at the next No Start
Spray ether into the engine and see if it starts
If it does and then dies, Spark is OK but fuel delivery is not working
If it doesn't start then no Spark
50/50

 

[Curious Hound]

Get in it and can't figure why the dash lights are on, apparently the brake lights don't work but when you press the brake pedal the dash lights come on......
Last edited by bossbob; Today at 01:02 AM.

What does it do when you use the turn signals or hazard flashers? How about when you turn the headlights on? I think I would start by checking the multi-function switch and flasher modules. Possibly a loose ground connection somewhere also.

 

[bossbob]

I was looking at it again this morning, It started right up and about 5 minutes later it just shut down and wouldn't restart. I depressed the valve on the fuel rail and it has pressure. I'll pick up a fuel pressure tester today and see what it's really doing. I'll check spark at the plugs later today too.

Didn't get a chance to check the turn signal switch, I'll do that tonight when it gets dark.

 

[bossbob]

I put a fuel pressure gauge on it, with the pump on its reading 35-36 psi, while running its reading 28-30 psi, the pressure gauge was leaking at the valve so it would probably have a bit higher pressure if the connection was sealed. (Autozone Rental)

Runs for about 5 minutes and dies, pulled the spark plug and it had spark. Waited 10 minutes and did the whole thing over with similar results, however I pulled the plug again and had no spark. Waited 20 minutes or so, and still no spark. I put the coil wire to ground and I might get 1 good spark and then no more.

What do you think is the coil toast????

 

[dirtymike]

I believe you have a bad pick up coil. Under the rotor cap there is a module with the three leads that the TFI module plugs into. It is pressed on. Dirty

 

[bossbob]

Dirtymike,

If I put a spark plug in the coil wire and ground it out I'm only getting one spark only, then nothing it goes dark. Is that normal for an ignition coil or should it spark multiple times?

If it is supposed to spark multiple times, then wouldn't that eliminate the pick up coil as if the spark is not getting to the distributor cap?

If the ign. coil is okay only sparking once, then I can see the problem being under the cap at the pick up coil.

Just thinking out loud.......

 

[RonD]

If an ignition coil has 12v on "+" and a Ground on "-", nothing happens

If you remove the Ground it will Spark, or remove the "+"
Each time you "power up" and then remove the power it will spark

That is what "points" did in the older distributors, unground the coil then ground it again
In electronic ignitions that is done by a Transistor like device, and electronic switch that grounds and ungrounds the Coil

Powering up the Primary Coil creates a magnetic field around the Secondary Coil, when power is lost the magnetic field collapses, which sends out the spark on the Secondary coil

 

[bossbob]

Good explanation RonD, so then the ignition coil is good, and the secondary (pickup coil) would be bad like DirtyMike mentioned....?
/

 

[RonD]

Primary and Secondary are both inside the coil

image here: https://nationalmaglab.org/images/education/magnet_academy/tutorial/ignitioncoil.jpg

 

[dirtymike]

Pick up coil not secondary coil. The pickup coil under the rotor sends a signal to the TFI and on to the ECU for engine management.

 

[RonD]

Pick up coil not secondary coil. The pickup coil under the rotor sends a signal to the TFI and on to the ECU for engine management.

Just a difference in the wording

The Hall Effect sensor is inside the distributor and it is, in real terms, a coil of wire, but haven't heard of it being referred to as a pick up coil, but it could be, because that is what it does, it uses a coil of wire to "pick up" a signal each time a vane passes by it.
This signal is called the PIP(profile ignition pickup)

TFI diagrams here: http://www.therangerstation.com/how...iv-electronic-engine-control-troubleshooting/

 

[dirtymike]

hall effect vane stator switch