OBD 1.5 w/ Mods

[Canyonero]

Hey guys, I'm getting out of one 60º project and into another and I'd like a little advice pertaining to the use of an OBD1.5 ECU on a modified engine.

I'm going to be selling my 1990 Isuzu Trooper with a 3.4L swap. I'm most likely going to be selling it to a friend and I want it to behave like a normal daily-driver car. Right now it's pretty aggressive at low throttle and it's a bit choppy when started in the cold. I could probably re-tune the engine and ECU to get it nearer to a stock configuration for hopefully a more linear and "normal" experience, but I'm thinking of doing something else - reinstalling the SFI/MPFI setup.

Quick sum-up of the current configuration:
3.4L Iron-head
4.3L TBI/Injectors (intake bored to match)
DIS
Crane H260 Cam
Comp 1.6 ratio rockers
Comp springs
Manifold-back free-flow exhaust (3" cat and flowmaster)

It's currently running TBI with a tweaked chip in the original '8062 ECU. I do have BPC adjusted for the change in displacement and injector flow, where most 3.4/TBI swappers just compensate using an adjustable fuel pressure. If I sell it with TBI, that's what I'll do (and re-install a dizzy so I can run a stock chip).

The other option is to reinstall all the Camaro SFI bits. When I first did the swap, I was running the engine with SFI and loved how it drove - but that was before the cam and rockers were installed. Will the OBD1.5 system fuss over the hotter cam and rockers and loss of the cam position sensor? I do have an original camaro cam that I could reinstall if I do want to get proper SFI back.

Or, I could use a '7727 - I'd just have to buy another one for my other 60º project.

I know the OBD1.5 isn't ideal for tuning, but with the mods I have, do you think it would it work acceptably?

[robertisaar]

the P66 V6 does NOT like it when there is no cam position signal...

that being said, there is a LOT of open space on the E-side, so a patch COULD be implimented to either force it into MPFI mode or fake the cam signal and have it attempt to run SFI....

no guarantees on how well either would work though.

if the MC were getting driven with any regularity, i would disconnect the cam position sensor and disable the DTC to see how it reacts.



otherwise.... if that cam had a cam signal, i wouldn't see any problems with it after a little bit of tweaking in the calibration.

[Canyonero]

I have the L32 engine from a 94 Camaro engine, not sure what the P66 you're talking about is. I don't know off the top of my head what OBD1.5 ECU they came with though. I thought I had read that the ECU would default to MPFI if there was no cam position. I'd prefer it not throw a CEL. I guess the question is if my cam, rockers and exhaust would be in the range of variance where the stock ECU would be able to perform normally and not throw a CEL.

[robertisaar]

I have the L32 engine from a 94 Camaro engine, not sure what the P66 you're talking about is. I don't know off the top of my head what OBD1.5 ECU they came with though. I thought I had read that the ECU would default to MPFI if there was no cam position. I'd prefer it not throw a CEL. I guess the question is if my cam, rockers and exhaust would be in the range of variance where the stock ECU would be able to perform normally and not throw a CEL.

the 93-95 3100/3.4 PCM is unique in that it is OBD1, uses two Delco P6 processors and has a flash PROM, which is why i just refer to it as the P66 V6(though GM called it the SFI-66U, which is still a unique identifier).

with no cam signal, the factory documentation states that it will still operate in SFI mode, only that it will guess at which cylinder is actually requiring fuel and inject based on that. whether or not it actually does this, i don't know, i've never had the opportunity to test it out and GM has been known to distribute half-factual information before.

with no cam pulse, it WILL trigger a SES light.