I have a '93 GMC 1500. It has recently had a tune up and is still having problems. Service Engine light is on and they said it is a code 42 which I'm told is a transmission code. when im driving it seems to not want to shift or increase at the rate it should right away when i first hit the gas. it will also sit at a high rpm until i let off the gas and then it will shift. the scan originally showed that the injectors were working great as well. i could use any help that is offered. thanks.

SOURCE: 2000 GMC Jimmy slow acceleration until 3000 rpms

you could check the fuel pump i recently had some problems with my punp after i replaced it where i would get to 3k rpms and it would sorta shut down and wouldnt go past it untill i let off the pedal

SOURCE: 1997 transmission Slow Acceleration

not sure if this is the answer yet but i have the same problem with the same codes i work at an auto parts store and a few of the techs that are customers have lead me in the direction of changing the ignition switch, i am doing it today will let you know if it solves the problem

SOURCE: i have 93 gmc 1500 truck with throttle bodey

Check for fuel pump operating, if running check the pressure. Fuel pressure springs are likely to fail in these TBI units.

SOURCE: my GMC Envoy 2004 .... RPM goes over 10 i

probably a problem with TPS sensor ot electronic pedal sensor

Jeffrey Turcotte

• 8991 Answers
• Posted on Nov 20, 2010

SOURCE: Hi I have a 98 gmc sierra 1500 with 5.7 vortec,

It's hard to find these small leaks. If you have a vacuum pump, there are a few tests you can run on the components of the system. See below.

TESTING

Vapor Canister
See Figure 1

1. Apply a length of hose to the lower tube of the purge valve assembly and attempt to blow air through it. There should be little or no air should passing into the canister.

1. Using a hand-held vacuum pump, apply a vacuum of 15 in. Hg (51 kPa) to the control vacuum (upper) tube. If the vacuum does not hold for at least 20 seconds, the diaphragm is leaking. Replace the canister.
2. If the diaphragm holds vacuum, attempt to blow air through the hose connected to the PCV tube while vacuum is still being applied. An increase of air should be observed. If no increase is noted, the canister must be replaced.

Fig. Fig. 1: Cross-section of the vapor canister


Fuel Tank Pressure Control Valve

1. Attach a length of hose to the tank side of the valve assembly and try to blow air through it. Little or no air should pass into the canister.
2. Using a hand-held vacuum pump, apply vacuum equivalent to 15 in. Hg (51 kPa) to the control vacuum tube. If the diaphragm does not hold vacuum, the diaphragm is leaking. Replace the valve.
3. If the diaphragm holds vacuum, attempt to blow air through the hose connected to the valve while vacuum is still being applied. Air should pass. If no air is noted, the valve must be replaced.

1. With engine temperature below 100°F (38°C), apply vacuum to the manifold side of the switch. The switch should hold vacuum.
2. Start and continue to run the engine until the engine temperature increases above 122°F (50°C). The vacuum should drop off.
3. Replace the switch if it fails either test.