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GMC 5.7 no spark/no fuel

K

kswillie

Member
93 2500 5.7 TB. Been setting for four days. Cranks but will not start. I can not hear the fuel pump when the key is on. Sprayed a little starting fulid in the TB with no results. Put a spark plug tester between the coil and the dist. cap no spark. Can a bad fuel regulator or pump keep the dist. from making spark? The fuse for the pump is good. Or can a bad ecm prevent the fuel pump form coming on? Kind or hard to belive they would go bad at the same time. I hate throwing parts at it.
 
When the key is initially switched "on", the 'puter energizes the fuel pump relay for about 3 seconds to prime the system.

Then, when you crank the engine, the 'puter senses pulses from the pickup coil in the distributor and turns the fuel pump back on, fires the sparkplugs, and pulses the injectors.

Start by determining for sure if the fuel pump relay is being activated at "key on", and if the fuel pump runs for 3 seconds.

If NOT, check all fuses related to the ECM and fuel system.
 
Start with dia. the no spark. You say you have no spark at the coil wire between the coil and the cap. Two possible problems. One you have a bad coil or a bad ignition module in the dist. The other problem in the dist. could be the pickup coil on the dist. shaft. I have seen very few with that problem. most are a coil or module. Fix the no spark first then look at the fuel. The ecm looks for spark to fire the injectors.
 
I would start by checking the fuses since there are in fact a fuse for both the ignition system and the fuel pump and maybe even a relay or 2. Seen problems like that and be a simple burned out fuse
 
usually is ign module or sometimes pickup coil ,I a lot of the time install new complete dist if things are looking bad they are pretty cheep and you can get them with cap and rotor and be all new
 
There are fuse links on the left side of the fire wall connected to a terminal strip. The fuses can corrode. Happened to my '94 2 winters ago. The terminal strip is in the engine compartment.
 
One other thing: The computer looks for an oil pressure signal from the sender behind the distribuitor (at least I think a '93 still has a distribuitor) and the engine will not start until the computer is satisfied.

I tried that on my '88 and sure enough, if the plug is off the sender it will not fire.
 

Not to create an argument but the only relation between the oil pressure switch and fuel pump is the oil pressure switch serves as a back up power supply to the fuel pump in case the fuel pump relay fails. It does not shut the fuel pump down, but can turn it on. The oil pressure switch can turn on the fuel pump once sufficient oil pressure is achieved ( approx 4 psi ).

If you have one of these trucks that has a intermittent or constant long crank to start, it might be due to the fuel pump relay or circuits. The long crank results from the time it takes to build up oil pressure and energize the FP circuit through the oil pressure switch.
 
At cranking and low idle speeds the ECM does not control the spark. That is all controlled by the ignition module until the engines reaches 600 rpm.
 
(quoted from post at 01:15:31 07/15/15) At cranking and low idle speeds the ECM does not control the spark. That is all controlled by the ignition module until the engines reaches 600 rpm.
Click to expand...
ots of interesting suggestions here, but not the one we experienced on our '92.
Put a code reader on it & it threw a temperature sender code. Replaced & it started.
 
(quoted from post at 02:37:23 07/15/15)
Not to create an argument but the only relation between the oil pressure switch and fuel pump is the oil pressure switch serves as a back up power supply to the fuel pump in case the fuel pump relay fails. It does not shut the fuel pump down, but can turn it on. The oil pressure switch can turn on the fuel pump once sufficient oil pressure is achieved ( approx 4 psi ).

If you have one of these trucks that has a intermittent or constant long crank to start, it might be due to the fuel pump relay or circuits. The long crank results from the time it takes to build up oil pressure and energize the FP circuit through the oil pressure switch.
Click to expand...

This is true.
 
(quoted from post at 05:47:31 07/15/15)
(quoted from post at 01:15:31 07/15/15) At cranking and low idle speeds the ECM does not control the spark. That is all controlled by the ignition module until the engines reaches 600 rpm.
Click to expand...
ots of interesting suggestions here, but not the one we experienced on our '92.
Put a code reader on it & it threw a temperature sender code. Replaced & it started.
Click to expand...

The ECM uses the temperature signal to determine the injector pulse width at cranking. If it was sending a signal that showed a hot engine there would not be enough fuel injected to easily start a cold engine. Likewise if you have a cold engine signal and the engine is warm it will probably flood when trying to start.
 
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