91-93 3.4 DOHC (LQ1) with OBD II PCM

[Series8217]

I'm considering upgrading to an OBD II PCM on my 3.4 DOHC V6 car. I have a 93 motor with 94-95 cam carriers so I have provisions for the cam position sensor. Not sure if I have the reluctor on the cam itself -- I need to check. I can add it if needed. Everything else is 91-93, including my throttle body and all engine sensors.

I have a manual transmission, but the 96-97 (OBD II) 3.4 DOHC V6 cars never came with manual transmissions... so there's no code for a manual trans.

The reason for this upgrade would be to permit datalogging with my lap timing / datalogging software, which has an OBD II interface.

A few points I know I need to deal with:
1) Cam position sensor -- I have 94-95 cam carriers so I have provisions for the sensor. I'm not sure if I have the reluctor on the cam; I'll have to check that.
2) SFI -- this will require a new injector harness. Not a big deal.
3) EGR -- if I recall correctly, the 96-97 EGR unit is PWM-controlled. I deleted the EGR on my custom intake manifold, but my smog-check intake has EGR on it. Can I control the 3-solenoid EGR or do I need to swap to the PWM EGR?

Questions:
1) Can I run the OBD II PCM in batch fire mode, in order to ditch the cam sensor?
2) Will my crankshaft position sensor work or do I need to add one on the harmonic balancer?
3) Should I use the 3.4 DOHC PCM or use something different? What if I want to run boost in the future?
4) Do I need to convert to MAF or is it still speed density? Is converting between MAF and speed density an option if not a requirement?
5) What other sensors do I need to add or replace? Second knock sensor? Post-cat O2 sensor? Fuel pressure?
6) What's the best tuning solution for the OBD II PCM?
7) What's the best way to permit good driveability with the OBD II PCM and a manual transmission? Is there a proven solution?

[The Dark Side of Will]

What datalogging package are you using?

Since you already have the BAR sticker, I assume you don't need to do anything special for emissions compliance except pass the smog check every 2 years.


3) You'll need the PWM EGR, unless you want to modify a lot of code. There might be an OBDII V6 app that uses the digital EGR, but probably not.

1) You can probably run the OBDII system batch fire by simply not connecting the cam sensor... but you'd have to disable the corresponding trouble code. I have no idea if that has further impacts to the system (limp home mode? Limited ignition advance?)

2) The OBDII setup uses both crank sensors... The ICM uses the in-block sensor. I'm not sure how dependent the PCM is on the ICM's crank sensor output or if it uses the 24x (18x) in the balancer exclusively.

3) EricJon262 may be able to help out here, as he's spent time figuring out a few things about interchangeability of the 60 degree V6, 3800 and Shortstar PCM's. You may be able to run coil per cylinder using the Shortstar code, for example.

4) AFAIK, anything GM made that has both MAF and MAP will run MAF or SD. It'll throw a code without either one, unless you disable that code. GM MAF's are straightforward to add to a system. The OBDII Northstar throttle body and the 3800 throttles have the MAF housing bolted directly to the throttle; I don't know if the OBDII DOHC throttle does the same or not.

5) You'll need OBDII knock sensor(s), as they have different impedance than the OBDI units. Not having post-cat O2's requires turning off the corresponding trouble codes... which means that the catalyst tests never pass and your car won't pass an emissions check... there may be a hack to make all the tests pass all the time. I don't think GM started using fuel pressure transducers until DI came out.

6) HPTuners or EFILive would be the most complete. There are various DIY efforts on the market, like TinyTuner.

7) Tune, tune, tune. Copying idle follower settings from the OBDI manual transmission tune would probably be a good start.

[ericjon262]

Questions:
1) Can I run the OBD II PCM in batch fire mode, in order to ditch the cam sensor?
2) Will my crankshaft position sensor work or do I need to add one on the harmonic balancer?
3) Should I use the 3.4 DOHC PCM or use something different? What if I want to run boost in the future?
4) Do I need to convert to MAF or is it still speed density? Is converting between MAF and speed density an option if not a requirement?
5) What other sensors do I need to add or replace? Second knock sensor? Post-cat O2 sensor? Fuel pressure?
6) What's the best tuning solution for the OBD II PCM?
7) What's the best way to permit good driveability with the OBD II PCM? Is there a proven solution?

I'm not as familiar with the LQ1 PCM as I am the 3800/60v6 pcm, so my answers will be in reference to the 98+ V6 PCM.

1)I doubt it would be that easy.
2)Ryan tried doing this, ditching the 24x crank sensor that is installed under the balancer and wasn't able to make it work.

Edit: if you are refering to the 7x sensor, it's fine, the problem will be if your timing cover has provisions for the 24x sensor installed under the balancer.

3) it may be your only option depending on if GM used a specific crank/cam sensor for them, I would find this hard to believe though.
4)of the obd2 PCM's I've looked at, they are primarily MAF based. there was a thread on 60V6 about converting to MAP based, but it never really took off.
5)the rear o2 can be deleted easy enough no fuel pressure sensor required.
6)I have several, and they all seem to offer about the same amount of tunable parameters, try and get a DHP cable and then download tiny tuner.
7)running the programming as close to stock as possible...

What are you trying to accomplish with the odb2 PCM? how fast do you turn your engine? you may exceed the bounds of the fuel and spark tables, they stop at 6400 RPM.

[Series8217]

What datalogging package are you using?

RaceChrono Pro with a Qstrarz 818XT GPS and Bluetooth OBDII interface

You may be able to run coil per cylinder using the Shortstar code, for example.

That would be nice!

[Series8217]

Edit: if you are refering to the 7x sensor, it's fine, the problem will be if your timing cover has provisions for the 24x sensor installed under the balancer.

I did replace my timing cover but I think its from an early motor. I don't rermermber seeing a place to mount a sensor.

7)running the programming as close to stock as possible...

There is no stock manual trans code.

What are you trying to accomplish with the odb2 PCM? how fast do you turn your engine? you may exceed the bounds of the fuel and spark tables, they stop at 6400 RPM.

7150 rpm redline. Possibly boost in the future.

[fieroguru]

I would suggest starting with the stock OBD2 ecm for the 3.4 DOHC application (even if its an auto) and wiring it up like is supposed to be (keep SFI). All of its tables will be very close to what is needed (like cold/hot start, timing map, fueling, knock, etc). You can then tweak the timing and fueling for the mods you have, turn off all the auto transmission codes, and then work on fixing the clutch in stalling issues. I have never looked at the OBD2 3.4 DOHC calibration, but generally speaking you can adjust the Base Running Airflow, the IAC park position while moving and/or the closed throttle timing to get it to be stall free when you push in the clutch. The OBD2 ecms are much, much faster than OBD1, so they can react to the clutch-in scenario and make the needed adjustments before it stalls out... even without the clutch pedal input.

The 3800's and LS4's never had manual factory calibrations either, but it doesn't take much work for the auto calibration to work well w/o stalling with the manuals.

[ericjon262]

I did replace my timing cover but I think its from an early motor. I don't rermermber seeing a place to mount a sensor.

the obd2 LQ1 uses a second crank trigger, much like the 31/3400, I am unsure whether the sensor is the same between the two, you'll have problems without it.

There is no stock manual trans code.

are you sure? 3.8 F-bodies PCM interchange and were offered with manual transmissions. there's a flag in the 31/3400 bin files for transmission type, manual being an option. There's also a flag for crank trigger type, and offers 24x/24x(shortstar), 7x/24x(31/3400), and 3x/18x(3800). I think more than just the hardware interchanges between them.

7150 rpm redline. Possibly boost in the future.

the 7150 redline would be my biggest concern, in the programming every table only goes up to 6400 RPM. right now, you'd be exceeding that by 750 RPM. It's a problem I spent some time trying to figure out how to correct for a while, and never found a valid solution. I'd like to give it another try, just need to find more time to work on it.

[ericjon262]

The 3800's and LS4's never had manual factory calibrations either, but it doesn't take much work for the auto calibration to work well w/o stalling with the manuals.

Factory manual 3800 calibrations exist, in fact, the "base tune" for my Fiero is partially based on one. 1996+ Fbody 3800 was offered with a five speed, 98+ PCM's interchange between them and the other GM V6 PCMs.

I would suggest starting with the stock OBD2 ecm for the 3.4 DOHC application (even if its an auto) and wiring it up like is supposed to be (keep SFI). All of its tables will be very close to what is needed (like cold/hot start, timing map, fueling, knock, etc). You can then tweak the timing and fueling for the mods you have, turn off all the auto transmission codes, and then work on fixing the clutch in stalling issues. I have never looked at the OBD2 3.4 DOHC calibration, but generally speaking you can adjust the Base Running Airflow, the IAC park position while moving and/or the closed throttle timing to get it to be stall free when you push in the clutch. The OBD2 ecms are much, much faster than OBD1, so they can react to the clutch-in scenario and make the needed adjustments before it stalls out... even without the clutch pedal input.

If I was a betting man, I would bet on the LQ1 running the same controls as the 31/3400, the obd2 LQ1 PCM interchanges with many other V6 applications (including the 3.8 V6 Fbody...) I would bet there are calibration options for manual transmission operation under the same PCM.

[The Dark Side of Will]

The 3800's and LS4's never had manual factory calibrations either, but it doesn't take much work for the auto calibration to work well w/o stalling with the manuals.

Factory manual 3800 calibrations exist, in fact, the "base tune" for my Fiero is partially based on one. 1996+ Fbody 3800 was offered with a five speed, 98+ PCM's interchange between them and the other GM V6 PCMs.

If I was a betting man, I would bet on the LQ1 running the same controls as the 31/3400, the obd2 LQ1 PCM interchanges with many other V6 applications (including the 3.8 V6 Fbody...) I would bet there are calibration options for manual transmission operation under the same PCM.

The last year of LQ1 production was '97. However, it sounds like the basic systems (crank triggering, etc.) persisted and became more homogeneous after LQ1 production stopped...

Do the manual trans 3800 applications have a clutch switch?

So it sounds like the "best" thing that could be put together for Steven would be 7x/24x crank triggering from the 60 degree V6, coil per cylinder from the ShortStar and manual transmission "awareness" from the 3800. It may even be possible to turn these options on in the stock LQ1 program... ?

As for the higher redline... The OBDI tables top out at fairly low RPM, but they have "adders" that change the top row table values linearly when the engine RPM is off the top of the table. I @$$ume that the OBDII systems work similarly. As long as the LQ1 peaks below 6400, such that the changes in airflow and ignition advance requirements with RPM are fairly linear and monotonic, it should be tunable via adders.

OBDI tables typically stopped at (I *think*) 4800 RPM. The only engine GM ran at the time that peaked higher was the Quad 4... it had a second set of "high RPM" VE tables to handle 4800+ elsewhere in the code. Obviously that was a software workaround not conceived when the original code base was written.

Actually... the MAF won't care about RPM, so it will take care of the fueling just fine. The ignition advance curve is typically flat above peak power, so the adders shouldn't have any problem with that.

Sounds doable *IF* all the stuff is built into the code.

What's the max RPM in the tables for the stock LQ1 calibration?

[fieroguru]

The 3800's and LS4's never had manual factory calibrations either, but it doesn't take much work for the auto calibration to work well w/o stalling with the manuals.

Factory manual 3800 calibrations exist, in fact, the "base tune" for my Fiero is partially based on one. 1996+ Fbody 3800 was offered with a five speed, 98+ PCM's interchange between them and the other GM V6 PCMs.

I was referring to the 3800SC's... they never had a stock manual calibrations (at least not in the US) and there are lots of them running a manual with the auto calibration.

[Sinister Fiero]

You can use the OBD2 PCM to run a 3.4 DOHC engine and a manual transmission. But I'm afraid you are going to need both the 1x Cam sensor AND the 24x crank sensor that resides behind the balancer. My testing on another OBD2 V6 (3100) revealed that when the 24x sensor was disconnected and even if all related trouble codes were disabled in the tune for it, it still had issues running correctly. So you're going to need that 24x sensor and I'm not sure how easy it is going to be to install that.

I also wouldn't advise trying to run an OBD2 SFI PCM without the cam sensor (ie: forcing it into batch fire mode) because I'm sure (as is with the case of disconnecting the 24x crank sensor), other aspects of operation are going to be impacted.

Only 2 OBD2 PCMs were used with 3.4 DOHC engines. 1996 model year and 1997 model year. Since 1996 PCMs aren't widely supported by the aftermarket, I would avoid using one. You can use the 1997 PCM instead. These same PCMs were used with most all other V6's in 1997 (ie: 3100s, 3400s, 3800s, etc).

Both 96 and 97 OBD2 PCMs use both a MAF and MAP sensor. The MAP sensor didn't do much unless the MAF sensor failed. But if you run boost, you'll need to keep the stock 1-bar MAP (since that is all the 3.4 DOHC OS will work with) and just use an appropriately sized or scaled MAF sensor to work with the amount of boost you are running. Tuning a MAF-based system (as these PCMs are) is easy to do and involves much less work than trying to tune speed density.

I believe the OBD2 PCMs require different knock sensor(s) than the OBD1 systems used. You will also need to make sure you get the correct knock interface module for the OBD2 PCM (which are replaceable). I'm not sure what part number knock interface module you need and if it is different than what was used with the 3100 and 3400 V6s, because I don't have that information. But if you can find a 97 3.4 DOHC car in the junkyard and get the PCM out of that car, it should have the correct knock module already in it.

I believe HP Tuners VCM Suite supports the 97 3.4 DOHC PCM (but don't quote me on that). I do know it can at least glean scan data from it.

I do have custom tuning software (TunerCat OBD2) which works with the 96 and 97 3.4 DOHC PCMs.

[Series8217]

You can use the OBD2 PCM to run a 3.4 DOHC engine and a manual transmission. But I'm afraid you are going to need both the 1x Cam sensor AND the 24x crank sensor that resides behind the balancer. My testing on another OBD2 V6 (3100) revealed that when the 24x sensor was disconnected and even if all related trouble codes were disabled in the tune for it, it still had issues running correctly. So you're going to need that 24x sensor and I'm not sure how easy it is going to be to install that.

I also wouldn't advise trying to run an OBD2 SFI PCM without the cam sensor (ie: forcing it into batch fire mode) because I'm sure (as is with the case of disconnecting the 24x crank sensor), other aspects of operation are going to be impacted.

Thanks for the input! I was hoping you'd chime in.

For the cam sensor pickup, do I need a different cam or did they all have flats for the sensor? I already have the correct cam carrier, so I can bolt in the sensor after modifying my valve cover or switching back to the original rectangular one.

It sounds like the first thing I need to do is look into the 24x sensor, as that is going to be the hardest thing to implement.

[The Dark Side of Will]

The 24x sensor is really just a matter of finding the parts. You'll need the front cover, balancer and sensor from an OBDII engine. If you find a '97 car in a junk yard and get the PCM from it, you can get the sensor, cover and balancer at that time also.

Swapping them onto your current engine is just bolts... A little more involved than just wires, but not bad.

[Series8217]

The 24x sensor is really just a matter of finding the parts. You'll need the front cover, balancer and sensor from an OBDII engine. If you find a '97 car in a junk yard and get the PCM from it, you can get the sensor, cover and balancer at that time also.

Swapping them onto your current engine is just bolts... A little more involved than just wires, but not bad.

Front cover is not "just bolts". It's an entire timing job, which can't easily be done with the motor in the car. Actually I don't think I can pull the front cover with the motor in the car even if the timing belt can be done. If I pull the motor I'm throwing in a 2.8T...

[The Dark Side of Will]

Timing belt has to be done every other week anyway, right?

I know it involves draining coolant and a lot of difficult access. My point was that it's straightforward and you don't have to make anything.

[draven]

I believe most of this may have already been answered but I've been researching and laying out plans for a haltech e11v2 in lieu of my 96 DOHC / 97 OBDII ecm..

From what I've been able to find out the 24x crank sensor is only used for low speed emissions, the 7x to the ICM and the 1x cam sensor are used primarily.
(fyi the 7x crank cannot be used against HalTech ECUs as quoted by their NA tech/sales rep, have to us the 24x with the 1x CAM on home)

I've got my 24x sensor and harmonic off but timing cover installed and can grab some upclose pics, etc... LMK

The 97 ECM was used on 3100s, 3400s, 3800s, and lq1s.

The 97 ECM can be tuned by HPTuner however only limited table access. TunerCat or its current relicensed incarnation can access most all of the 97 ECM functionality.

MAP is used as a backup for a failed MAF.

MAP only is capable but only after disabling the limp code. (hearsay only)

The Post cat O2 sensor can be disabled as it is on mine, by Sinister if I'm correct or maybe it was that guy in texas, lyle ? lloyd? whichever...

EMC209 did in fact replace his timing cover while still in the car.. gotta be a PITA though... I'd drop the engine as after thinking about everything bolted to that monstrosity while sitting on my engine stand..

mine runs ("ran") on a stick after recoding by one of the two above and is "ok" with a few glitches. While the clutch is engaged and decelerating from mid to high rpm, once the the clutch is engaged and the revs come down it cannot maintain idle and shuts down.. Idle shoots up to 2k often while putting around between gears. both could probably be tuned out..

If I had the hardware I'd be happy to give you an image of the code in my ECM. Couldn't justify ordering TunerCat or HPTuner for 600$+ when an E6X or E11v2 could be had for only 2-3 hundred more.. Hell I'd be happy to part with my 97ECU however I plan on using that to start and break in my current 96DOHC rebuild currently under assembly and I operate slower than a herd of turtles in a river of peanut butter..

FYI, I do have a haltech E6X and harness for sale, 2nd owner out of a turbo IS300 with a current test bench receipt from Haltech

[ericjon262]

Do the manual trans 3800 applications have a clutch switch?

Yes, I have a pinout, and it is labeled as a "clutch anticipate switch"

http://www.gearhead-efi.com/Fuel-Inject ... CM-pinouts

I would just copy the info over, but the formatting gets lost...

also, FWIW, the L67 bin files have the manual transmission flags as well. and the each bin, be it shortstar, 31/3400 L36, L67 has an "engine type" flag, along with a crank sensor flag, to change sensor type. I assume "engine type" changes the ignition style between each engine.

[ericjon262]

just thought about this, and you could probably run ignition coils from a Vortec 4200 with the shortstar programming. ditch the plug wires altogether.