What would cause a speed surge??

[leenigen]

Usually I'm cruising along at a steady speed (between 50 and 65 or so) and will suddenly get a drastic surge in speed like I just floored it. Most of the time I'm holding the throtle steady or even slightly letting off when the surge happens. After completely letting off the gas then getting back on it the engine will stay reved up for a while before settling back down (like it just downshifted then upshifted again - but didn't). I'm thinking maybe its a lift pump problem but am bafled at the moment. Any ideas?

'94 4 door hard top. 6.2L NA (jasper)

[NoMoGMPG]

Check your fuel tank vent first (located behind the overflow container), then air filter, then the fuel filter. After those, then I would look at the lift pump, pinched or deteriorated fuel lines, and injection pump condition.

[leenigen]

The air and fuel filters were just replaced about 1000 miles ago. I'll check the vent line. Thanks

[EXH1X5]

Originally posted by leenigen:
Usually I'm cruising along at a steady speed (between 50 and 65 or so) and will suddenly get a drastic surge in speed like I just floored it. Most of the time I'm holding the throtle steady or even slightly letting off when the surge happens. After completely letting off the gas then getting back on it the engine will stay reved up for a while before settling back down (like it just downshifted then upshifted again - but didn't). I'm thinking maybe its a lift pump problem but am bafled at the moment. Any ideas?

'94 4 door hard top. 6.2L NA (jasper)

If your '94 is VIN # 156048 or higher AND has factory installed cruise control, you may want to contact your friendly local HUMMER Dealer to find out if the applicable "Cruise Control Safety Recall" has been performed.

[NoMoGMPG]

Originally posted by EXH1X5:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by leenigen:
Usually I'm cruising along at a steady speed (between 50 and 65 or so) and will suddenly get a drastic surge in speed like I just floored it. Most of the time I'm holding the throtle steady or even slightly letting off when the surge happens. After completely letting off the gas then getting back on it the engine will stay reved up for a while before settling back down (like it just downshifted then upshifted again - but didn't). I'm thinking maybe its a lift pump problem but am bafled at the moment. Any ideas?

'94 4 door hard top. 6.2L NA (jasper)

If your '94 is VIN # 156048 or higher AND has factory installed cruise control, you may want to contact your friendly local HUMMER Dealer to find out if the applicable "Cruise Control Safety Recall" has been performed. </div></BLOCKQUOTE>

Good call, Jim.

[leenigen]

Well I don't have cruise so thats not the problem. I checked the fuel vent line and thats okay too. How often should that filter on the vent line be replaced though? I can't remember that ever being replaced. I'll keep poking around but I'm not too sure what to look for.
This problem occured just after replacing the glow plugs and controller. I think thats probably just a coincidence but maybe its pertinant info.

[NoMoGMPG]

The fuel tank vent looks like a filter but it is a check valve, it needs to be cleaned out occasionally. You may need to have the injection pump checked out, possibly the fuel solenoid malfunctioning.

[leenigen]

What do you mean by the fuel solenoid?

[NoMoGMPG]

Originally posted by leenigen:
What do you mean by the fuel solenoid?

On the injection pump, there is a fuel shutoff solenoid that controls fuel flow and a cold advance solenoid.

[leenigen]

Okay, I've located the run solenoid which I assume is aka the fuel shut off solenoid and the cold adance solenoid. Is there any method to test these. Obviously I'd like to avoid bringing it in if at all possible. The manual only helps for replacement not testing and thats not first on my list of things to do.

[leenigen]

p.s. how much faster is the idle when cold or what is the differance in engine behavior. I've had a suspicion that the cold advance wasn't working well before. I've heard that the solenoid isn't powerful enough to pull the throttle itself but if you push the peddle and let off before starting it's able to hold it. I haven't ever noticed any differance, although now that i have new glow plugs it does start better in colder weather but no idle differance besides the usual diesel cold clatter.

[NoMoGMPG]

The cold advance should net you about 900-1000 RPM when cold. I don't know the test method, sorry. But you might want to contact Dave Breggin at BlueHummer.com. He's pretty good with the older N/A's.