My truck does not start sometimes

[RayInAlaska]

I am having a weird problem with my truck, a 1988 GMC Sierra step-side. The motor is a 350 TBI that was rebuilt at a local shop a few years ago, but the truck is not driven very much, and the motor now has around 25,000 miles of driving.

This past winter on a very cold night I drove my truck around 20 miles, an turned it off after parking at one of the local stores. When I came back about 15 minutes later and turned the key to start the motor, the starter turned the motor as usual, but it did not start. I tried several times without success, so I had the truck towed home. About a week after, I decided to recharge the battery and then tried starting it again, and it started without any trouble.

Today I replaced the battery because the one in the truck is very old and it does not seem to hold a charge very long. I also checked the alternator’s power output, which was a tad over 14 volts (the motor started just fine). I left it running for a couple of minutes, and then drove around 10 miles. I noticed that when turning the turn signals on, all the gage indicators (white bands) would move down and up with the flasher (same speed), but I made it home fine, parked it, and replaced the oil and filter. Then I started the motor to check for oil leaks, but the motor stopped running when dropping from high to low idle. It did that two times. On the third try it started again, and I held the gas pedal to keep the RPM around 1,500, but then died about 5 seconds after releasing the gas pedal. Now the motor won’t start, just like it happened when I drove it to town in February.

When trying to start the motor in this condition, it feels as if there is either no fuel, or no spark, or the timing is off, or there is no compression (the motor turn at a fast speed, but does not start).

a. What would cause the gage indicators to drop almost all the way down and then back up at the same speed as the flasher?

b. Any ideas on why the motor does not want to start now, then starts and runs fine maybe in a day or two?

[b454rat]

Does the fuel pump come on? If it doesn't, kick the tank, sometimes that knocks em back to life. Least then you will know what it is.....

[ChevyTech]

Start testing things to eliminate possible problems.

As stated, see if you can hear the fuel pump run for a few seconds when you turn the key on.

See if it has spark when it won't start.

See if the injectors spray fuel when it won't start.

Take a look at this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=669201

[RayInAlaska]

Originally Posted by ChevyTech

Start testing things to eliminate possible problems.

As stated, see if you can hear the fuel pump run for a few seconds when you turn the key on.

See if it has spark when it won't start.

See if the injectors spray fuel when it won't start.

Take a look at this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=669201

Thank you for the link. I guess I will have to figure what's going on with the truck. At least it's just about summer and I have another vehicle to drive. But it will probably take some time before I figure things out, since I am tackling several projects at the moment.

[RayInAlaska]

Just went outside, and had my wife listen for the fuel pump when I turned the key, one click before cranking the motor. The pump came on, and then I turned the key and the motor started and ran normal high idle.

Something else, the battery voltage indicator stayed on 14 volts, unlike yesterday when I turned ON the turn signal. I will explain further what happened:

a. The battery voltage gage-when the motor is running without any trouble-points right at the 14-volt mark. But when I drove the truck yesterday and turned the turn signal on, the all the gages were bouncing up and down at the same speed as the turn signal flasher, and when turning the signal off at the end of the turn, the voltage gage stayed somewhere below 13 volts, and all the other gages stayed below their normal place. For example, instead of 3/4 tank full, it was indicating perhaps 1/2 full tank of fuel. But the digital voltage gage at the column always stays a tad over 13 volts (I have a 3-pack set of digital gages at the column), even when the volt gage shows less than 13 volts.

b. Close to home all the gages, including the voltmeter, jumped to their normal place.

c. I also checked the voltage from the alternator at the battery (yesterday when I replaced the battery). This is an over powerful 220-amp alternator (was there when I bought the truck). I checked the voltage with a Fluke multimeter.

I do have a Viper RPN 474V electric door opener and FOB, and this system has an engine immobilizer tied in. However, as far as I can tell, all it does is to prevent to motor from starting if the door is manually unlocked. But in this case all I have to do is to turn the key to ACC, and then press the unlock button on the FOB, at which point the alarm's warning light goes out. So I don't think that the motor no start condition, or just turning itself off has to do with the alarm, but something to do with maybe a power loss to the fuel pump.

I will be checking other things in the near future (in a week or two), and will keep you posted. Right now I am so busy with chores at home and at work that it's somewhat ridiculous

Thanks for your help.

[speedygonzales]

I have encountered many alarm/disabler problems in the past. Including one that had partially been removed and we never knew it till ten years later, when we couldn't start our family SUV.

I highly recommend you remove it before doing anything else.

When your gauges pulsate with the blinkers, that indicates you are not getting enough current to the entire electrical system. You said you checked the battery voltage over 14 when the engine is running so we at least assume the alternator has enough output.

I suggest you check the connections for power and ground to the engine and the frame. I added electric fans to mine and needed more current. My 140 Amp alternator did the same thing until I added another ground from the battery to the engine and just for good measure, I added another line from battery positive to the alternator.

Once you have eliminated those known issues (even the alarm), then you can be on the look out for odd occurrences. If the engine acts up again, do as chevy suggested, check for loss of spark and then loss of fuel spray at the TB injectors.

One thing I despise about TBI is no fuel pressure port. If I had a TBI, I would install either a permanent gauge (which I currently have on my Vortec) or an easily accessible schrader valve(which Vortecs have anyway).

With a permanent gauge mounted on the A pillar indicating pressure was fine, I was able to quickly diagnose a bad cap and rotor the day after christmas. I pulled the coil wire and saw plenty of spark and immediately knew the cap was bad. 20 minutes later and $40 lighter, we were on the road to the relatives. Funny how the day before it started and ran fine.

[RayInAlaska]

Originally Posted by speedygonzales

I have encountered many alarm/disabler problems in the past. Including one that had partially been removed and we never knew it till ten years later, when we couldn't start our family SUV.

I highly recommend you remove it before doing anything else.

When your gauges pulsate with the blinkers, that indicates you are not getting enough current to the entire electrical system. You said you checked the battery voltage over 14 when the engine is running so we at least assume the alternator has enough output.

I suggest you check the connections for power and ground to the engine and the frame. I added electric fans to mine and needed more current. My 140 Amp alternator did the same thing until I added another ground from the battery to the engine and just for good measure, I added another line from battery positive to the alternator.

Once you have eliminated those known issues (even the alarm), then you can be on the look out for odd occurrences. If the engine acts up again, do as chevy suggested, check for loss of spark and then loss of fuel spray at the TB injectors.

One thing I despise about TBI is no fuel pressure port. If I had a TBI, I would install either a permanent gauge (which I currently have on my Vortec) or an easily accessible schrader valve(which Vortecs have anyway).

With a permanent gauge mounted on the A pillar indicating pressure was fine, I was able to quickly diagnose a bad cap and rotor the day after christmas. I pulled the coil wire and saw plenty of spark and immediately knew the cap was bad. 20 minutes later and $40 lighter, we were on the road to the relatives. Funny how the day before it started and ran fine.

Thanks for all the hints. I will taking care of some of them in about two weeks. This week and next I am getting another old truck (1981 F-150) for the fast approaching salmon season. I plan to be gone for four days at the end of next week, but when I come back the first thing I will do is to loosing, clean, and re-instal any negative ground connections on the negative side of the battery.

I do have a set of electric fans on my truck, but this is the only time in a couple of years that I have seen the gages, including the volt gage, drop so much when I turn the turn signal. The 220AMP alternator, Stinger Model 7861, does a great job when the electric fans come on.

Thank you again. I sincerely appreciate it.