sudden unexpected acceleration

[Van]

The 97 suburban experiences "SUA". Sudden unexpected acceleration.At random, and now more frequently: Rpm increases , blows black smoke, and if in drive , takes off like you stomped on it. Also happens in park or reverse & with cruise control de-fused. R&R of the APP had no effect. Codes 0236 & 0753 have shown when scanned. I'm stumped. Any ideas?

[cesguz]

Hi Van, did you already check your booster, maybe that

[charliepeterson]

I would say your Injection Pump has failed. You are covered under GM's Special Policy #00064D for 11 years or 120,000 miles with NO deductable.
This Injection Pump is drive by wire all electronically controlled. There is no way this truck should speed up with no additional accelerator movement. This condition can occure without setting any trouble codes. The problem is inside the Injection Pump.
Just make sure the lift pump is working before you bring the truck to the dealer. At the front of the truck next to the thermostat find a "T" valve with a rubber hose. Put the hose into a bucket and open the valve with the truck running. This is the water bleed hose from the fuel filter housing. You should see a steady stream of fuel coming out, this confirms lift pump operation. If the truck stalls the lift pump is dead. Power to the pump comes from the oil pressure switch after the truck is running. The switch is down behind the fuel filter housing.


Good Luck

[Van]

Thanks all for the info. have checked lift pump allready.
wiring harness and connections... fuel filter... water in system...some sensors (by connect and disconnect)...the basics... suspected an injection pump or pmd problem...and was hoping for some confirmation before shelling out the big bucks. Whats the special tool to rotate the pump to remove it, is it necessary? easily fabricated? the 'burb has 156,000 on it and original inj. pump and injectors so I'm not complaining. Anyone else had this problem, it's pretty hairy in a crowded parking lot!

[ucdavis]

Van,
I agree w/Charlie. First code is boost related & could happen w/cracked or leaking vacuum tubing, etc.
Second is tranny which isn't related to acceleration.
That leaves no failure related codes, & therefore probably fuel delivery trouble.
Special tool isn't req'd if you have the sense not to use the FSO solenoid for leverage in rotating the IP. Alternatively, use a magnum set of channel-lock pliers that can grab the whole IP to rotate it.
If you are trying to get the new IP properly timed, look @ the IP flange on top left by the bolt, there is a fold or angle in the otherwise curving edge of flange. Measure dist from that fold to the alignment mark on the block side & install the new IP w/exactly that same distance & you shouldn't even need to retime the new IP.

[Van]

ucdavis,
Looks like I'm swapping an IP this weekend. Thanks for the pointers.

[Turbine Doc]

Van,
when you say takes off a lot or a little, something that happened to me last weekend while swapping PCM's engine accelerated for no reason and stayed high, I finally found out what those 2 unidentified wires coming out of center PCM plug were. They are the fast PTO speeds, in center connector B7 1360rpm & B8 1070rpm shorted to ground engine steps up, probably not related to your problem but it is a quick check behind glove box see if you have 2 loose wires bare connector on it that could be intermittently grounding out and accelerating your engine on it's own

[n3qik]

The higher PTO RPMs are disable when foot is on brake or truck is in drive.

[lupey6.5]

my 94 did that just as the crank position sensor was going bad it set a slew of codes also but just think if the computer doesn't know where the crank is or its speed---nothing with the electronic injection works right. that sensor is on the driver side front of the block near crank.
the wires on mine pulled out b4 the sensor did so i had to thread a screw into the sensor to pull it out.