Hi Everybody! I just finished the 3.4L swap in my '91 Firebird and I've got a rather unique problem: my engine runs too well.

It's been sitting for about a year since I began this project, but when I started it for the first time yesterday it fired right up and immediately revved to redline as if you've got the pedal pressed to the floor (scared the ******* out of me). With much difficulty, I've got the initial timing set to about 10* (which slowed the rev) but it will still get up to redline within 10 seconds of starting, even with the EST disconnected. I have verified that the throttle body is completely closed during these revs. There are no check engine codes (other than EST). Any thoughts on what might cause this? I haven't found anyone with an issue quite like this yet. The car ran like a dream prior to the engine swap

For reference, here's what I've done to the car so far:
3.4L F-Code Block, fully rebuilt and overbored
DIY ported heads (followed instructions on this forum)
Mellling MTC-5 camshaft
Mellling hydraulic lifters
Crane 99848 valve springs + retainers
Howards Cam 93010 +.050 locks
22# TPI Injectors from SouthBay
Stock rocker arms
Stock pushrods
Stock intake & throttle body from my original 3.1L MPFI
EGR delete
AIR delete
Canister delete
EBL-P4 ECM for tuning (I'm using the supplied 3.1L bin and so far I've adjusted displacement, injector size, smog stuff, filled main Injector voltage offset table with data from this forum, and filled slow injector voltage offset table with zeros).
Wideband o2 (not connected to EBL-P4 yet).

Any suggestions will be greatly appreciated...

 

When I read your post my first thought was ; Vacuum Leak .

 

I had this thought as well. Has anyone had any vacuum leaks around SouthBay's TPI injectors? They came with those flat o-rings and were a pretty loose fit in the intake manifold...

I'm going to try plugging the IAC valve and then the whole throttle body to narrow it down.

 

Update:
I pulled the injectors out again and they were way loose. I'm not sure if the TPI systems used a different diameter injector or what, but I replaced all the o-rings with the o-rings from my stock injectors and now they fit like they should.

Unfortunately that didn't solve the problem though.

Next, we partially covered the throttle body with a 2x4 to narrow down where the air is coming from and that did stop the revving, so the air is coming in through the throttle body. We pulled the IAC valve, cleaned the passage, and bought a new IAC valve; but the problem persists.

I'll post a datalog of one of the revs later today and maybe someone more experienced will see something amiss that I do not.

 

Here's a recent datalog and the bin I'm using. I bought a 1-bar map sensor to try out on the off-chance my $9.00 Chinese 2-bar was causing issues. I've also adjusted the AE PW tables for my 22# injectors per instructions I found on this forum. Neither resolved the revving problem. If anything, it revs faster now .


Does anyone know if the IAC valve can even flow enough air to allow the engine to get to redline?

 

I'm not sure if I read that right...you blocked off the whole tb and it still revved? If yes, then vacuum leak. Make or buy a cheap smoke machine (they can be diy made, google it) and check it. I'm pretty sure it's a leak and you need to find it, it's clearly getting too much air.

 

No, covering the throttle body stops the revving. By covering it partially with a piece of 2x4, we were able to manually achieve a rough idle.

 

I can't read the files right now but what are your iac counts? In other words, is the computer trying to shut the iac? Try blocking off the iac and just use the throttle blades? I still wouldn't rule out vacuum leak because no matter what, it won't rev without the air. I'm not very familiar with the v6 hardware but they pretty much all troubleshoot and operate the same.

 

IAC shows up in steps for me. It stays at a steady 99 steps until about 2200 RPM where it starts to drop. By 3487 RPM (when I shut it off) it had come down to 79 steps.

 

Your datalog above is titled for 1-Bar, your Bin file is set for 1-Bar, but the MAP sensor you're using in the Datalog is a 2-Bar (2.3 volts key on). Straighten that out first, then throw up another datalog if the problem continues....

- Rob

 

Gonna necro my own thread here:

My data logs show a different map sensor because I own both a 1-bar and a 2-bar map sensor. I had swapped them out and adjusted the flag in the bin just to see if it made a difference. You can use a 2-bar map sensor in an NA car as long as the bin flag is set for a 2-bar map sensor.

In case anyone is interested, I finally found the problem! One stud was out of place in the intake manifold which caused the lower intake plenum to be lifted up by about 1/8th of an inch

Corrected that and the car fired right up and idled fine. Thank you to everyone who lent their suggestions!

Let the tuning commence...