Very intermittent no start

fishEH

Well-known member
Jan 26, 2009
6,333
8
Lake Villa, IL
Just got back from 2 weeks in Colorado in my '94 manual D1. Only real issue was a no start on 2 occasions.

First was at about 12,000ft. Parked at the upper 4wd trailhead for Mt Lincoln. Hiked to the summit and came back down. No start. It would crank fine and the fuel pump was running. Couldn't check pressure at the rail due to no schraeder valve. Reset the inertia switch bit still wouldn't start. Fortunately I turned around and parked facing down the trail before hiking. I was able to release the handbrake, give it a slight push downhill, and pop the clutch to get it started.

Second time was about 20 minutes after pulling into a campground. Went to start the truck to run my air compressor and no start. Waited about 40 minutes and it fired right up.

Any thoughts?
 

jymmiejamz

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Callsign: KN4JHI
Dec 5, 2004
5,387
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30
Los Angeles, Ca
Coolant temp sensor would probably be one of the first things I would look at as well as the stepper motor. When I have a crank and no start with 14CUX I like to unplug the inertia switch and try cranking it with the pedal to the floor. If it starts for a second you know you have an overfueling problem or not enough air to the engine.
 

fishEH

Well-known member
Jan 26, 2009
6,333
8
Lake Villa, IL
So both times it sorta started/caught but not quite, with me pumping thw pedal slightly. So overfueling/air starvation sounds possible.
 

jymmiejamz

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Callsign: KN4JHI
Dec 5, 2004
5,387
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Los Angeles, Ca
The best way to confirm the coolant temp sensor is to look at the live data. Most of the time when they fail it will read really low which makes the engine run full rich. sometimes the connectors get corroded or crack. Next time it happens, you can just unplug the sensor. Mine failed in Utah and I made it all the way to California with it unplugged.
 

fishEH

Well-known member
Jan 26, 2009
6,333
8
Lake Villa, IL
The best way to confirm the coolant temp sensor is to look at the live data. Most of the time when they fail it will read really low which makes the engine run full rich. sometimes the connectors get corroded or crack. Next time it happens, you can just unplug the sensor. Mine failed in Utah and I made it all the way to California with it unplugged.
I've been meaning to put together a RoverGauge for it. Stock gauge read ok, but we all know how that can be.
 

Jimmy

Well-known member
Apr 10, 2006
547
0
Aurora, CO
It's been awhile for me, but I've occasionally had a tough time restarting at altitude. What usually does it for me is to release the pressure in the gas tank via the cap.

EDIT: Noticed my sig is gone. Have the same - '94 D1 manual.
 

jymmiejamz

Well-known member
Callsign: KN4JHI
Dec 5, 2004
5,387
20
30
Los Angeles, Ca
I've been meaning to put together a RoverGauge for it. Stock gauge read ok, but we all know how that can be.
There are two coolant temp sensors on your truck. One is for the gauge and one is for the fuel injection ECU. The connector that looks like a fuel injector connector on the intake is the one for the fuel injection ECU.
 

XCELLER8

Well-known member
Sep 21, 2009
210
0
my 95 has a similar hot start issue and usually stepping on the gas pedal gets it going.....with mine anyway I'm leaning toward the temp sensor / too rich mixture cuz when it fires up there is a strong smell of partially burnt fuel....flooded
 

discostew

Well-known member
Sep 14, 2010
4,524
11
Northern Illinois
It wouldn't start while you cranked it but started right up when you push started it? I wonder if that was just a coincidink or a clue. The coil if I remember correctly gets full on 12 volts when cranking to boost the spark, then gets a lesser voltage thru a resistive wire once its running. I think the module also switches and does something different when cranking.

That's full on puzzle palace shit though.
 

kk88rrc

Well-known member
Coolant temp sensor would probably be one of the first things I would look at as well as the stepper motor. When I have a crank and no start with 14CUX I like to unplug the inertia switch and try cranking it with the pedal to the floor. If it starts for a second you know you have an overfueling problem or not enough air to the engine.
Along with the CTS, check the fuel temp sensor. Helps to control fuel mixture on hot starts.
 

Grenade

Well-known member
Oct 8, 2015
86
0
Vegas
So, I have been battling somewhat of a similar problem, but mine has a problem of the Fuel Relay dropping in and out. I have trouble shot the issue to the Ground from the ECU is not able to hold the load on the coil side of the relay. This can happen at almost any time and its somewhat frustrating. Sometimes it is hard to restart but then other time it starts right up with zero problem afterwards.

I have a newer GM fuel pump in it that runs great, I wonder if the load on the fuel pump is more than the relay can hold. I've swapped the relay with others that are known to be good, but it seems the problem just follows it over. I have a new Bosch 40 amp relay that I will try but its been good lately since I installed a waterfall diode on the relay. `

Mine is a 95 which should be close but if you have any questions just PM me and ill be glad to answer.
 

BDM

Well-known member
May 23, 2005
234
5
East Coast
Have ever replaced the whole fuel sensing unit? I’ve had the same trouble recently. Replaced the pump and still didn’t help. Talking to Will Tillery, sounds like it might be a bad return valve in the sending unit itself. Going to test out a whole new unit next week to see if it fixes.

Btw my fuel pressure would drop off immediately after turning off which lead us to believe the above. Hope that helps
 

fishEH

Well-known member
Jan 26, 2009
6,333
8
Lake Villa, IL
I haven't. Outside of Colorado last year I've driven it less than 500 miles on the last two years. I can hear the pump running, but unfortunately there's no valve on the rail for checking fuel pressure.
 

discostew

Well-known member
Sep 14, 2010
4,524
11
Northern Illinois
Check spark when it does it. The coil or the distributor is more likely to be the problem. Since you hear the pump run, seems a stretch to think it doesn't make pressure intermittently.
 

fishEH

Well-known member
Jan 26, 2009
6,333
8
Lake Villa, IL
So went out yesterday evening. Wouldn't start the first couple times but sounded close. Loosened the fuel cap but nothing hissed out. Found the ECU Coolant Temp sensor and the plug was really loose. Pulled the plug off. Tried starting and this time it fired up. It was really chugging and rough at first. CEL popped immediately, Code 14 - Coolant Temp Sensor. Not a big surprise since it was unplugged.

I drove the truck around the neighborhood and it seemed fine. Parked it, shut it off, and restarted it a few times without issue.

So I still have no idea what the problem was/is.

How do I clear the CEL on a 14CUX truck?