# 1990 GMC 1500, 5.7 engine hard starting problems



## dlooking (Aug 9, 2009)

I have 2 stating problems.

Vehicle has Throttle Body Injection with only 83k miles.

1) Cold starting - when having set overnight or for at least 2-3 hours, it will start 1st lick, but may immediatly die or I might catch it with the throttle & keep it running. If it dies when cold, it will usually start again after considerable continueous cranking, but never on 1st lick as when totally cold. Once started and warmed up, it will run fine until I stop the engine.

2)Hot starting - after starting, warming up & shutting down, I can immediatly restart again with considerable cranking, not on 1st lick. If it sits 10 - 20 minutes, say shopping in a store or getting gas,it will start again with considerable cranking. If it sits 1-2 hours, it might start on 1st lick, then die or I might just crank with no hope of starting until I wait longer and have not drained the battery.

It had a surge problem at idle when 1st starting cold. The auto parts salesman said the surge meant the Throttle Position Sensor was going bad. For $30, I thought it might be a simple fix and might not have to catch the throttle on cold start to keep it running. The surge apppears to have ceased, but it will still die if I do not catch it.

It had code reading 44 which means it is or was running lean. The salesman said it needed a good fuel injector cleaning fuel additive. Again for $10-$20, I thought a simple fix, but no changes.

I also tried a can of Sea-Foam sucked in through the brake booster vacuum. No changes.

Does anyone have any ideas on how to troubleshoot and solve these problems.

Thank You


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## octaneman (May 13, 2009)

Hi dlooking


The computer has registered a code 44 which indicates the O2 sensor is not functioning properly. The O2 sensor measures the amount of oxygen going through it and it has to be removed and visually inspected for any deposits on it. A black color indicates that the engine is running rich, if it has a whitish color it means that engine coolant or silicone deposits are present, a brownish color means that its normal wear and tear. This can be verified by using a scanner and looking at the cross counts. The cross count voltages should be between 0.45 and .9v , if the readings are not within spec it would indicate a faulty O2 sensor which will have to be replaced.

Cleaning the fuel injectors was a good idea but if you have to keep the gas pedal pressed down when you start either hot or cold indicates a different problem. By your description, the problem lies within the fuel pump. The pump will work for a brief period, the windings will get hot or the impeller not working properly causing fuel pressure to drop. Hook up a fuel gage and test the pump with and without load. Turn the ignition on ( engine off) and listen for any abnormal noises such as wheezing or high pitch sound, that will indicate the pump is dying causing the intermittent hard starting.

post back your findings.


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## dlooking (Aug 9, 2009)

Hi Octaneman,

I thought you might be the one most likely to reply, after reading other threads trying to solve the problem without having to post a question.

As for the O2 sensor, I already had taken it out and visually inspected. It was a nice light brown like a well firing spark plug with no deposits. I did find a hole in the muffler past the cat converter. Will that produce the Code 44? Anyway, a new 1 was only about $20, so I replaced it. I do not understand what you mean by using a scanner. Do you mean a voltmeter? And what are cross counts? So far my cheap fixes have added up to around $100, but it still runs the same.

As for fuel delivery, if it starts when hot, I do not have to keep the gas pedal down. When cold, if I catch the engine before it dies, I only have to hold the pedal for 5-10 seconds. Then it will warm up on it's own. I have to start it with the gas pedal off and depress the padel once it starts. How and where do you hook up a fuel guage? Can the problem be in the fuel filter? Another cheap fix that keeps adding $ up, but much simpler than a fuel pump. R&R a fuel pump is a nasty job. I had to do it on a 93 Suburban with a fuel pump that just quit. It would be a simple job if GM had just put an access hole in the bed of the truck.

I have also read that there is a fuel regulator on the throttle body itself. Could that be the problem?

I do believe it is a fuel delivery problem, not an ignition problem, but I have read that the ignition control module takes it's signal from the TBI. Maybe I've just read to much.

Thank you for all your help.


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## octaneman (May 13, 2009)

A hole in the exhaust can set a code 44, depending on the size of the hole, it creates back pressure through the exhaust which the O2 sensor ( depending on its location) can pick up. 

A scanner is a tool that reads codes from the engine computer when the check engine light lights up, it's connected to the ALDL connector under the dash. You can rent a scanner at some auto parts suppliers or you can ask the person at the counter if they can retrieve the codes for you, it's usually done for a small fee. 

Cross counts are referred to the oxygen sensor's ability to switch from rich-to-lean at a specific time period in seconds. When the engine is running, the oxygen sensor oscillates from rich-to-lean, this is measured in voltages, these voltages are measured from a computer scanner as cross counts, the optimum range the O2 sensor has to operate is from 0.45 to 0.9v to determine if the oxygen sensor is switching from lean-to-rich according to engine performance. There is also a way to manually test the O2 sensor by using a cheapie propane torch and a DVOM. Connect the positive leed to the O2 wire the negative to the body of the O2, light the torch and place the tip on the hottest part of the flame and watch the meter voltages change by counting in a 5 second interval. If it doesn't change the sensor is not functioning. 

A blocked fuel filter can cause the problem you are experiencing, any restriction in fuel flow will have a direct effect on how the engine runs. To test the fuel system you will need a fuel pressure tester. Since the engine is a throttle body injection system, you will also require a T fitting to connect the fuel line to the gage and to the the inlet fuel port. On TBI's there are 2 lines, 1 is straight in , the other at an angle. The one thats straight in is the inlet, thats where you hook up the gage the other is the return. Once it's connected, you take readings to determine if it's the fuel regulator, or the pump itself. On throttle bodies the fuel regulator has a goldish color shaped like a cup under the injectors. 

To test the regulator, you will have to follow a certain test procedure to determine if it's at fault. If by some chance it is faulty, you will have to tear the TBI apart and buy the gasket kit for it. 

I can understand that changing the fuel pump is a hassle, but given the symtoms your describing, the fuel pump is the primary suspect IMO.


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## dlooking (Aug 9, 2009)

Hi Octaneman,
I am sorry it took so long to get back to you, but I got called out of town for work and just got back. I decided an easy and cheap fix might be the fuel filter, so I replaced it. The truck ran a little better than before, but still not right. I never did do a fuel pressure test. I was getting ready to hook it up when I got called out of town. While I was away, my 17 year old son, whose truck it is anyway, decided to put a fuel pump in after I told him I thought it was the fuel pump. He drove it until the tank was on empty before changing it out. Then he couldn't get fuel pressure to the tbi. He put 5 gallons of gas in the tank, but by that time he had discharged the battery. That's how it was when I got home. I charged the battery at 2 amps overnight. The beast started up 1st lick and runs fine. Thanks again for all your help. P.S. I don't think my son will ever change out another fuel pump, but maybe when he gets older and has more patience he'll realize that it wasn't all that bad.


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## octaneman (May 13, 2009)

Thanks for letting us know the problem is solved... Nice job. :4-clap:


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## 1990GMCVan (Oct 29, 2014)

octaineman, are you still on the site?


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