1994 chevy silverado starting problems.

[jcb428]

My 1994 chevy silverado was running just fine until a couple of days ago. It's driven every day. I parked it and went out of town for 5 days. When I returned home, I went out to start my truck, but it wouldn't start. It cranks very strong, but doesn't start. I tried starting it several times. I sprayed a little starting fluid in the carburetor to see if the truck was getting spark and not getting any gas. The truck cranks and runs with no problems, and it runs until i turn it off. I try to crank it again and the same problem occurs. I spray just a little starting fluid in the carburetor and it cranks right up again. I drive the truck for 30 minutes and it did not give me any problems. I did not notice anything abnormal. I go back home and turn the truck off and guess what, my problem is back again. I don't know where to go from here. Any help will be appreciated. My truck has a 5.7 liter engine and is 2wd. The only thing I have done is change my air filter.

[rambler]

check your fuel filter, check your fuel pump, have they ever been replaced? replace the pump with a AC/DELCO only,, and get the sock filter that fits the end of the pump as well... it is sold seperately do not get a aftermarket fuel pump or you'll do it again in 12-18 months...

of course, may be new plugs and wires would hurt either...

any check engine codes?

[tommie]

I had worked on one of these trucks do this a long time ago after the engine had been detailed. water had damaged the TPS (throttle position sensor) and the computer thought that the driver was holding the gas pedal to the floor in "clear flood mode" and the computer had turned off the injector drivers, and was waiting to see a lower TPS voltage....

The TPS is a 3 wire sensor, one wire is a ground, one wire is a 5 volt reference signal sent from the ECM, and the last wire is the feedback wire from the TPS that varies from about .5-.75 vlots at closed throttle to 4.5-5 volts at wide open throttle.

this can be easily checked with a volt meter after removing the air cleaner. (with the sensor plugged in)

or you could simply unplug the tps and see if the truck starts. when the sensor is unplugged, the ECM uses a default value to operate the engine

this is where i would start, since you said it runs fine after you start it by spraying some starting fluid in the TBI.


there could be other problems like listed above... but I would check this first, then check the fuel system/fuel pressure....

[ChevyTech]

It sounds like your fuel pump relay is not working.

When you turn the key to the on position without cranking the engine you should here the fuel pump run for a few seconds.

The ECM controls the fuel pump relay.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.


When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through an oil pressure sensor/sender. Once the engine has oil pressure the fuel pump will get power even is the relay has failed. This is most likely why it will run if you use starting fluid to start it.

If the fuel pump relay is bad the computer should have store a trouble code 54.
A code 54 happens when the computer does not see power on the circuit from the fuel relay to the fuel pump, when the computer is sending power to the relay to apply the relay.

Here are some web sites with the basics on retrieving codes without a scan tool or code reader.

Poor drawing of ALDL but ok instruction + codes
http://www.cfm-tech.com/gm_tbi_trouble_codes.htm

OBDI terminal identification
http://robertpowersmotorsports.frees.../ALDL_plug.jpg

OBDI illustration and instructions
http://www.troublecodes.net/GM/

I see it’s your first post. Welcome to the message board.

[jcb428]

Thanks for the replies. I have not had time to get out today and check anything else because it have been raining all day. I did check the fuel pump when the problem first began and I can hear it come on once the ignition is turned on.

[ChevyTech]

If the fuel pump does run when you turn the key on, then the relay is working, and you should do the following:
Replace the fuel filter
If the problem is still there
Test the fuel pressure
If the fuel pressure is good see if the injectors are being triggered which is often done with what is called a “noid“ light.

Another posibility is the coolant temp sensor has failed and it giving a hot reading so to little fuel is being injected to start the engine. When the sensor fails it usually goes the other way and reads to cold all the time.

The coolant sensor may not set any trouble code unless the reading is off the end of the specification chart. I can post specifications if you have an ohm meter to test the coolant sensor.

[jcb428]

I have figured out that my tps(trottle positioning sensor) and iac(idle air control valve) are working. The fuel pump is also working fine. When the truck is having problem starting no fuel is being sprayed from the injectors. I removed the gas line from the carb and gas came out with good pressure. Therefore, my injectors are not being trigger at times. I am trying to figure out why. I may end up replacing them. I am still needing help on this issue if anyone has any information that will help me. If i solve this problem I will let you all know what fixed it. Thanks again.

[ChevyTech]

The computer needs to receive a distributor reference pulse from the distributor module to trigger the injectors.
It is possible for the module to produce spark without the computer getting a reference pulse. A bad distributor module or wiring between the module and the ECM/PCM can cause this.

With the key on there should always be power at the injectors. The ECM grounds the other side of the injector, to make the injector open.

Many stores like NAPA in my area will test the module for free if you bring it in.

Make sure when you install or reinstall the distributor module that you use heat sink compound/grease under it. The grease helps dissipate heat from the module. Without it, the module will fail.

[jcb428]

I haven't been online in a few days, but I replaced the module and I think the pulsator(i think that's what it is called. it was a white ring with wire coiled around it and it was connected to the module.) and my problem is now fixed. Thanks for all the help.

[ChevyTech]

Glad you got it repaired.

Thanks for the update.

(i think that's what it is called. it was a white ring with wire coiled around it and it was connected to the module.)

Pick up coil.

It is very common for the modules to fail.

The pick up coils do not fail very often and are much more work to change.

[mitch1965]

I did the same T/S scenario, loosened fuel line, observed good flow, thought pump was ok, on my '96. I finally tested the pressure at the fuel rail, and found the pressure to be 50psi instead of the recommended 60+. I replaced the pump and it fired right up.