Cold start

[DeanWest]

I've been working on a 1994 K1500, 5.7, auto, 98,000 miles that has been sitting on the ranch for over a decade without running.

I've managed to get the old truck running but I'm still having some problems.

Primarily, when I try to start it after sitting overnight, she refuses to start, only cranking over. When I squirt starter fluid in the carb (TBI), she fires right up. During the day, I can fire her up at any time.

I've tested and replaced fuel pump, injectors, fuel filters, temp sensor, a new computer (old one burnt). I have not replaced the fuel regulator and don't know how to test the same. Pressure is good, getting good spark.

Any suggestions would be appreciated.

[Blue Bowtie]

If the TBI feel line pressure is 11-13 PSIG, the regulator is probably O.K. Since priming with external fuel will permit a cold start, cold enrichment is in question. You've reportedly replaced the CTS, but what does the ECM think the coolant temperature is? Also, is the IAT sensor functioning? Any error codes?

[DeanWest]

Thanks for the quick response.

I'll check to see if I can run a test on the IAT. That makes a lot of sense. Especially since I didn't know that the sensor existed.

I can't seem to run a diagnosis on my truck. Some have told me that it's not supported. I even bought another cable that would fit the underdash connection but nothing appears...so, I cannot connect to the ECM.

Thank you again...much appreciated.

[Blue Bowtie]

1994-95 PCMs (probably 16197427) are somewhat unique. Communication usually requires a Tech II or similar bi-directional scanner to retrieve data. Short of that, the sensor itself can be tested with an ohmmeter.

In researching this further, it appears that some '94 TBIs did not have an IAT/MAT sensor, whereas the '94 PFIs did.

[DeanWest]

Thanks.

I did discover that the old truck doesn't have an IAT but it does have a MAP. I'm going to check the voltage on that sensor this morning. If it's defective, one of the results is a no start in the morning.

Thanks again.

[Schurkey]

Originally Posted by DeanWest

when I try to start it after sitting overnight, she refuses to start, only cranking over. When I squirt starter fluid in the carb (TBI), she fires right up.

1. Does the fuel pump prime when the key is turned from "Off" to "Run"? The pump should run for two seconds. If it doesn't, there's trouble in the ECM, the fuel pump relay, or the wire harness connected to the fuel pump relay.

2. Verify that the fuel pump runs when cranking (before you have oil pressure.)
If the fuel pump relay system isn't working right, the truck will have to crank long enough to build oil pressure. Then the oil pressure switch bypasses the relay to power the fuel pump.

3. How old is the gasoline? Old gasoline will not vaporize properly, it'll be hard to start especially when cold.

[DeanWest]

When I turn key on, I can hear the fuel pump running but instead of a short two second run, the pump continues to run. That has me concerned. I installed a new pump relay when I installed the new pump so that should be good to go.

I tested the MAP this morning and it gets 5volts. Just to check, I disconnected the MAP and tried to start but same results, crank but no start until I added starter fluid. After she started , she ran a little rough.

I found another sensor next to the carb (left of carb facing truck) that I don't know what it does.

That sensor has two vacuum lines coming out, one to the EGR and the other to the barrel of the carb.

I wasn't able to drain all of the old fuel but have added approx 10 gallons new. Maybe I should add some alcohol to the fuel?

[Schurkey]

Originally Posted by DeanWest

When I turn key on, I can hear the fuel pump running but instead of a short two second run, the pump continues to run. That has me concerned.

Yes, that is concerning. A few vehicles have a "Hot Fuel Module" that provides an extended prime--about twenty seconds. The pump must not run continuously; that'd be a safety hazard if the vehicle were in a collision. It'd pump fuel creating a fire hazard. Except for the two (or twenty) second prime, the pump should shut off if there's no oil pressure (engine stalled) or if the distributor isn't providing an RPM signal to the ECM.

Originally Posted by DeanWest

I found another sensor next to the carb (left of carb facing truck) that I don't know what it does.

That sensor has two vacuum lines coming out, one to the EGR and the other to the barrel of the carb.

Not a sensor. It's an EGR solenoid. It allows (or blocks) vacuum to the EGR valve.

Originally Posted by DeanWest

I wasn't able to drain all of the old fuel but have added approx 10 gallons new. Maybe I should add some alcohol to the fuel?

I'd be driving--or at least running--the truck to burn all the old fuel. Verify that the fuel filter doesn't plug up as the last of the old fuel is depleted.

You'll want to start running Top Tier (high detergent) fuel in the future.

Connect a scan tool, verify the outputs of all the sensors--coolant temperature, MAP, TPS, RPM, O2 voltage, alternator voltage, etc.

Originally Posted by DeanWest

I tested the MAP this morning and it gets 5volts. Just to check, I disconnected the MAP and tried to start but same results, crank but no start until I added starter fluid. After she started , she ran a little rough.

The ECM supplies 5 volts to the sensor. The sensor signal should be about 1/2 volt (0.5) back to the computer. It's the signal that's what you're looking for, not so much the power supply.