1997 GMC 350 Truck wants to stall on quick accelleration after initial start u

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  #1  
Old 06-17-12, 09:14 PM
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1997 GMC 350 Truck wants to stall on quick accelleration after initial start u

Help. I have a 97 gmc with a 350. The problem is after initial startup and I back out of the driveway the truck feels like it is stalling out under quick acceleration. It is fine the rest of day. I have replaced fuel filter, plugs, wires cap , rotor, egr with oe, cleaned MAF sensor, checked for vacum leaks. I don't have any codes set, the vehicle idles fine. It just bothers me to start my day off that way. Any help would be appreciated. It never dies or stalls out completely.
 
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Old 06-18-12, 07:24 PM
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One possible issue could be with the fuel pump operation. A cold pump could be acting up, because it is getting weak, and there is also a known issue with fuel pump wiring harnesses on that vehicle along with the pump. If there is a valve on the fuel rail, one approach would be to take a pressure reading on the cold engine, and later on a warm engine. The pressure should be the same in both cases and likely around 50 pounds. A failing pump system will not show a fault code in most cases. Not saying this is what it is, but something else that should be eliminated or confirmed.
 
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Old 06-19-12, 05:19 AM
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In addition to nox's fuel pump suggestion, I would suggest you get a scanner on it that can read real time data. Couple of things come to mind - coolant temp sensor and O2 sensor, but I wouldn't go throwing parts at it without getting a read on how they are performing first. I'm thinking it's running lean when cold instead of slightly rich until it warms up. Weak fuel pump would be sort of same symptoms.
 
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Old 06-19-12, 04:39 PM
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Normally when a coolant sensor is faulty it does not move from the higher resistance 'closed loop' when the coolant is cold into 'open loop' as the coolant warms, and so maintains a higher level of resistance affecting the voltage sent to the PCM. When in closed loop mode the default program in the PCM calls for the engine to run rich rather than lean, and hence most people find problems once warmed up as the engine starts to show performance signs of running too rich including poor fuel economy. While a fault code does not always show up unless the sensor is out of operating range, and the OP mentioned that there were no codes coming up, my guess is still around fuel pump performance that needs to be confirmed. The OP might also want to try and clean the injectors with something like the Seafoam additive as if they are not providing enough fuel when the engine needs to run rich at cold start similar problems could also occur.
 
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Old 06-19-12, 05:50 PM
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Yeah, that's why I was suggesting a real-time data look-see to check what things are doing.
 
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Old 06-20-12, 08:18 AM
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update 97 gmc sierra 5.7

I checked fuel pressure on truck. with key on pressure is 52. With engine running at idle the pressure holds at 55. When I turn the key off the pressure slowly drops. after about 30 min the pressure has gone to 34. Is this normal and how long should the pressure hold before bleeding off.

I don't have a scanner just a code reader and the forums. What would you recommend and would a novice be able to use one?
 
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Old 06-20-12, 04:46 PM
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To me it still sounds that your pump is on the way out but that is still only my best guess. Normally with the key on the pressure should read 60 to 65 lbs. and when running should read over 50 Below 50 and the engine will not start. After 5 minutes the pressure should hold between 40 to 45 lbs. If it is lower than that, though you didn't mention if it was after 5 minutes you either have a leaking pressure regulator or a leaky injector. Fuel pumps on these trucks generally do not have a long life especially if the vehicle has run with a low tank a few times.
 
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Old 06-27-12, 10:34 PM
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The operating fuel pressure for 1997 gm V6 and V8s was 45 to 48 lbs/sqin if you were reading 52 then your problem is possibly being caused by a bad fuel pressure regulator. With the fuel pressure that high then the engine would be so rich that the pulse time on the injectors may not be able to get short enough to get to an except-able fuel ratio and is basically forcing the engine to run in a rich condition and that would cause a stumble on acceleration. The OBD2 system in 1997 didn't have the most advanced diagnostics as that was the 1st generation of the OBD2 and requires a much more extensive diagnostics tree to isolate the faults.
 
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