Truck runs rough

[94singlecab350]

Hi,I have a 1994 obs with a 5.7 truck runs rough.when the weather get extremely hot,like right now it’s 115 she has trouble starting and staying on she will crank hood but jsut doesn’t want to start.she always surges and it’s so frustrating.sometimes when I drive her and turn her off I leave her sitting for about 30 mins to 2 and a half hours and I try to start it and she will start run terrible I have to step on the gas for to stay on and when I step on the gas she rev limits like at 3000 rpm’s.CAN SOMEBODY ON HERE PLZ HELP ME FIGURE THIS OUT.thank you

 

[HotWheelsBurban]

Hi,I have a 1994 obs with a 5.7 truck runs rough.when the weather get extremely hot,like right now it’s 115 she has trouble starting and staying on she will crank hood but jsut doesn’t want to start.she always surges and it’s so frustrating.sometimes when I drive her and turn her off I leave her sitting for about 30 mins to 2 and a half hours and I try to start it and she will start run terrible I have to step on the gas for to stay on and when I step on the gas she rev limits like at 3000 rpm’s.CAN SOMEBODY ON HERE PLZ HELP ME FIGURE THIS OUT.thank you

Check all your electrical connections, could be a bad (corroded)battery cable or terminals. Also could be the fuel pump giving you a heads up that it's not gonna be working too much longer.
My trucks are Vortecs, not TBI, but I've had a similar problem on them that, the first time was the cables and a problem with the starter, second time was the fuel pump.

 

[HotWheelsBurban]

Another thing to look into: when was the last time up and what was replaced? Worn out cap and rotor will create a lot of issues and if left unreplaced long enough, can take out the coil or module.

 

[94singlecab350]

Don’t think it’s the starter she cranks nice and strong but when she turns on she runs rough.also she doesn’t throw any codes.thank u for replying

 

[97K1500Silverado]

I have a similar issue with my 97 k1500 vortec 5.7. Runs great and never misses a beat until it’s over 90 out and when you go to restart after the engine is at normal operating temp it will start, run for a second then die. Only way to keep it running is to immediately give it gas and keep rpm about 1500 or more then it will run fine until you shut it off for a few mins and go to restart.

After replacing the coil, ignition module and checking all the grounds and connections still the same issue only when it’s very hot outside.

I think I may have finally solved it! The Vortec trucks and possibly the TBI trucks as well, Have two coolant temperature sensors the one on the side of the block that is a single wire connection at the sensor is only for the temperature gauge. The two pin sensor that screws into the water neck on the intake is for the computer and this is what a scan tool will read.

When the truck wouldn’t start, and it was hot out, I had my scan tool and no codes at all even when it fired up and died. The temperature on the scan tool was reading correctly, but then I saw -40 flash for a few seconds and then it went back to reading over 200. I’m going to replace the temperature sensor that goes into the water neck. Hopefully that finally solves my hot start problem and yours as well!

 

[94singlecab350]

I have a similar issue with my 97 k1500 vortec 5.7. Runs great and never misses a beat until it’s over 90 out and when you go to restart after the engine is at normal operating temp it will start, run for a second then die. Only way to keep it running is to immediately give it gas and keep rpm about 1500 or more then it will run fine until you shut it off for a few mins and go to restart.

After replacing the coil, ignition module and checking all the grounds and connections still the same issue only when it’s very hot outside.

I think I may have finally solved it! The Vortec trucks and possibly the TBI trucks as well, Have two coolant temperature sensors the one on the side of the block that is a single wire connection at the sensor is only for the temperature gauge. The two pin sensor that screws into the water neck on the intake is for the computer and this is what a scan tool will read.

When the truck wouldn’t start, and it was hot out, I had my scan tool and no codes at all even when it fired up and died. The temperature on the scan tool was reading correctly, but then I saw -40 flash for a few seconds and then it went back to reading over 200. I’m going to replace the temperature sensor that goes into the water neck. Hopefully that finally solves my hot start problem and yours as well!

So I disconnected the sensor next to the neck and she runs at a high and won’t die should I just replace it??

 

[97K1500Silverado]

So I disconnected the sensor next to the neck and she runs at a high and won’t die should I just replace it??

It’s an inexpensive part to replace. When the coolant temp sensor goes bad, it will read -40°. This causes the computer to add a crap load of fuel because it thinks it’s super cold outside when your truck is running like crap do you smell a bunch unburnt of fuel out the exhaust?

Disconnecting the sensor is different than the sensor reading the incorrect temperature. The computer knows when the sensor is disconnected and the computer will go into a fail safe open loop mode where it uses preprogrammed tables for air / fuel delivery.

Next time your truck doesn’t want to start when it’s hot unplug the coolant temp sensor. Does it run fine then? If so, definitely replace the sensor.

 

[Schurkey]

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
   
2. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Make sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.
   
3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle. The service manual set can be downloaded from the links in the Sticky thread section of the Engine forum on this web site.

 

[94singlecab350]

U

UPDATE, so I notice that when the truck surges and is about to stall when I spray starting fluid into the filter she will stop surging and stop tryna stall.Is it safe to say it’s a fueling issue.