Engine revving high??

[92gmcsierra]

I do not have a chip. But the shop I took it to took a computer from a junkyard and put it in.


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[great white]

So, to back this up, an intake manifold gasket was changed and then it started with higher rpm?

Is this during idle only?

Is this with it in park or drive or both?

Very unlikely it's the ECM since all they did was change an intake gasket.

It's far more likely something is unhooked or pinched around the intake manifold area.

Do you have the original ECM? MEMCAL is the "chip" that plugs into the board. It carries the calibration information for the truck. Each truck has it's own calibration stored on the MEMCAL and the actual ECM is universal to all the trucks that use that part number. If they moved your MEMCAL into a new (IE: junkyard) ECM it might not be seated properly, could have a bent pin or worst case scenario: they static shocked it.

The MEMCAL is under a plate on the ECM. Looks like this:

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Either way, changing out the ECm for an idle problem right after you did an intake gasket change is one hell of a bonehead move and makes me question their competency.

Given that, they may have done something else bonehead like pulling off the TBI and causing a vacuum leak at the base, or pissing around with the IAC pintle and messing it up.

At this point in the game (IE: they've mucked around with it) it's hard to say what it is.

Start at the beginning and make sure there is nothing unhooked or pinched (IE: vacuum lines, electrical wires, etc) in the engine bay....

 

[BoxerPitMix]

Hmm I remember dealing with that at one point with a buddy's truck.
Here's some stuff I found through google.. Dunno if it'll help or not.

http://repairpal.com/gm-obd-code-51

http://www.fullsizechevy.com/forum/...92-z71-trouble-code-51-prom-memcal-error.html

 

[92gmcsierra]

I had them do an intake manifold gasket and about a week and a half earlier it started doing this. It is a manual and I idles high and is also giving it gas when I am in any gear. Not sure if they kept my original MEMCAL or not. All three times they worked on it it stopped idling high for about a week and a half then started it back up again.

Now when the check engine light comes on and I give it gas it kind of sputters.


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[great white]

I had them do an intake manifold gasket and about a week and a half earlier it started doing this. It is a manual and I idles high and is also giving it gas when I am in any gear. Not sure if they kept my original MEMCAL or not. All three times they worked on it it stopped idling high for about a week and a half then started it back up again.

Now when the check engine light comes on and I give it gas it kind of sputters.


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Ah, so it was "surging" BEFORE the intake gasket change. That's a little bit different scenario.

Now that sounds like it could be a MEMCAL problem.

Likely corrosion on the pins or worst case it could be an actual fault with the MEMCAL. It doesn't take a lot of oxidation to cause problems in these types of connections.

You also have the added possibility of an insertion error since they would have remove/installed it with the ECM change.

If you're comfortable with it, disconnect the battery and access the ECM behind the glove box. Open the plate on the ECM by removing the two screws. Remove the MEMCAL and check for bent pins. Take a bit of rubbing alcohol and a q-tip and carefully clean the pins. Alternatively, you can use a spray called "de-oxit". A pink eraser also works, it's just a little rough for me the way most guys go at it. Then reinsert the MEMCAL into the ECM. Push evenly across the two ends, making sure it is seatly firmly.

Close it all up and then hook up the battery. I follow this procedure when "restarting" a cold ECM (since the power was removed): turn the key on but not the engine for about 60 seconds. Then turn the key off and let it sit for 5 mins. Then turn the key on and wait 60 seconds, then start the truck.

That is not strictly required, but it gives the ECM a chance to run any systems tests and poll any modules it needs to before you try and get it to run.

Make sure you touch your hand to bare metal on the chassis to equalize any static potential differences between yourself and the truck before opening the ECM and mucking around with the MEMCAL.

It's also worth checking your ECM ground to make sure there is no corrosion there either. Bad grounds cause all kinds of problems. On my 1998 diesel, the ECM harness ground is on the passenger side rear intake manifold bolt. Likely the same for yours.

 

[92gmcsierra]

No it was running perfectly fine before the intake manifold gasket.


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[great white]

No it was running perfectly fine before the intake manifold gasket.


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OK, your post #14 says something different....

 

[92gmcsierra]

Sorry I meant to say later not earlier.


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[DCorvin]

I think that's got to do with the computer they replaced. If you want something done right you have to fix it yourself. Shops don't care about your truck bat all they just want your money and get it out the door. Trust me.

I HATE having to take my truck to these places. Something always comes back messed up.