3.4L SFI/MPFI in Trooper, again...

[Canyonero]

Yeah, I know, it's been in there for like seven years. But I'm going to start fiddling with it again so that I can make my Trooper reliable before I dig into another car. I've been having an electrical issue, which I suspect is just a loose ground somewhere, but I liked how the Trooper felt with SFI and I want it back.

A few things are different from last time I had the SFI installed: I have a crane H260 cam, comp springs and 1.6 ratio rockers now (no cam sensor lobe). I would like to keep my mechanical fan, which won't clear the 3.4L intake - backup plan is to do what I did before, running two 10" fans mounted low.

I still have a full harness set up for the original 1994 OBD1.5 ECU, but I also have a harness made up for a '7727 (or whichever is the underhood version) which I had tested-started previously before I reinstalled my TBI (I wanted to get my Trooper back on the road for snowboarding season, but I always intended to return to MPFI).

I now have a variety of parts from 2.8/3.1 RWD that I may be able to use to make things fit better. I had them test-fit before I reverted.

Here are a couple old pics, I'll try to do better about taking pictures this time around...

[Canyonero]

I'm kind of tempted to re-install the Camaro cam and run the regular OBD1.5 ECU as SFI. I know the OBD1.5 isn't ideal from a tuning perspective, but I'd kind of like this truck to just run like a factory engine (not to say that couldn't be done with a 7727).

[robertisaar]

could be done with either and run equally well. i've never tried running the P66 V6 PCM in non-SFI mode, so i don't know how it would react with no cam signal.

[Canyonero]

Back when I did this the first time, someone said that it would revert to MPFI and not throw a CEL if the cam sensor were missing, but I can't confirm or deny that. Seems that it would be an issue for any of the 94-95 Camaro owners if didn't work. I first had it running as a bone-stock 3.4L with SFI, since I've installed the cam/springs/rockers it's only been run with TBI.

It's kind of a hassle to pull the cam. Troopers have a smallish engine bay so the radiator, AC condensor and grill have to come out to pull the cam. BUT, my other Opel which is getting a Gen2 60º from a Cavalier Z24 may benefit more from the hotter cam. Gen1 and Gen 2 can use the same cams right?

[Guest]

Yes, the same cam will fit in both gen1 and gen2. The only issue, is as you've discovered in the 3.4 gen1, that loses cam sensor with most aftermarket cams.

Personally, I'd leave the cam, and run MPFI. SFI is really only an emissions device.

[Canyonero]

I think the Cavalier engine is only MPFI anyway. But it probably is more trouble than it's worth to swap the cam back.

[Guest]

Yes, genII is MPFI only.

[robertisaar]

with 1 exception, yes.

i've confirmed the existance of a 1993 only(probably W-body only at that as well) california emissions LH0 that uses a PCM similar to that used on the 93-95 3100s and indeed has a cam sensor and operates in SFI. at the same time, there were also 93 3.1s built with california emissions that used a 16149396(ala the 91-93 3.4) or compatible.

[Canyonero]

Where is the ECU on a Cavalier anyway?

[robertisaar]

in-cabin. i want to say behind/under the glovebox area.

[Canyonero]

Cavalier should have a '7730 right? I have a '7727 already, I'll probably use that on the Trooper if I don't go with the OBD1.5.

[robertisaar]

yes, cav would be 7730.