OBDI vs. OBDII ECU's - Timing Advance/Retard or Other Benefits?

3162 Views 33 Replies 7 Participants Last post by Steve Jarvis, Feb 1, 2002

Spool

Discussion Starter · Sep 17, 2001 (Edited)

What are the differences between an OBDI vs. OBDII ECU in the way they each handle timing advance/retard and other engine control functions?

I find that I need to reset the ECU to restore the car to full power after a day running in hot temps...it's an OBDII '97.

When the ECU takes out timing, does it store these settings and use them indefinitely until the ECU is reset in both OBD I & II?

The real question is...what benefits are there in swapping my OBDII to an OBDI ECU? Would a swap actually improve the performance of the car or would it negatively affect the way my car runs since it came with the OBDII ECU.

I would appreciate any feedback on this one.

Thanks for the help!

1 - 20 of 34 Posts

Grant

· #2 · Sep 17, 2001

Ask Andi B. about problems with swapping.

As for the differences, no one knows.... The OBD2 does give timing back, it just takes some time.

Spool

Discussion Starter · #3 · Sep 17, 2001

Grant:

Sounds like a bad idea...

ANDI:

What's the word on the ECU swap?

Thanks!!!

G

· #4 · Sep 17, 2001

I swapped my OBDII ECU for an OBDI ECU and the only problem I had was the TRAC light flashing and TRAC not functioning. I unplugged the TRAC ECU connectors and that cured the TRAC light problem. So basically everything functions properly, but the OBDI swap will eliminate the TRAC.

Andi

· #5 · Sep 17, 2001

QuikSilverTT said:
I swapped my OBDII ECU for an OBDI ECU and the only problem I had was the TRAC light flashing and TRAC not functioning. I unplugged the TRAC ECU connectors and that cured the TRAC light problem. So basically everything functions properly, but the OBDI swap will eliminate the TRAC.

Do you have an EGT gauge?

When I tried an OBD1 ECU in my '98TT, my car ran much leaner as if it were staying in closed loop (13:1 on the wideband o2, on boost, like Scott Smith's car). EGT's went from ~650C at the top of the DP on a long pull to ~710C at the top of the DP on a long pull.... not good.. I couldn't change the AF at all even by modifying the MAF signal w/ various fuel computers.

Some '98s seem to do this, others don't... that's why I'm asking...

Andi

G

· #6 · Sep 19, 2001

I've got an EGT guage, but I have not tried it with the OBDII ECU. With my OBDI ECU, I've never seen anything above 1200F(~650C). But I also do not have an aftermarket fuel computer to try and play with a/f ratios.

The OBDI ECU I have is a used G-Force I purchased from a friend with a 94TT T04R. He called G-Force and had them burn 2 new PROMs for stock timing and stock fuel with the exception of speed cut, boost cut, and rev limit at 7600rpm. Since I had heard mixed opinions on G-Force tuning, I decided to have them put everything back to stock except for necessary items(i.e., fuel cut, boost cut and speed cut.

Andi

· #7 · Sep 19, 2001

QuikSilverTT said:
I've got an EGT guage, but I have not tried it with the OBDII ECU. With my OBDI ECU, I've never seen anything above 1200F(~650C). But I also do not have an aftermarket fuel computer to try and play with a/f ratios.

The OBDI ECU I have is a used G-Force I purchased from a friend with a 94TT T04R. He called G-Force and had them burn 2 new PROMs for stock timing and stock fuel with the exception of speed cut, boost cut, and rev limit at 7600rpm. Since I had heard mixed opinions on G-Force tuning, I decided to have them put everything back to stock except for necessary items(i.e., fuel cut, boost cut and speed cut.

650C is okay. That means your car is running pretty close to optimal IMHO.. (I'm assuming the 650C is at the end of a long pull to 150mph, not a short 3rd gear blast to 90 or a 4th gear romp to 120)...

Back when I had an OBD1 ECU, I could easily see 700C by the end of a 40 to 120 pull. The wideband o2 said I was running 13:1. Not cool.

FYI I tried 4 different combinations with the same results: MAF with no fuel computer, S-AFC with MAF, VPC by itself, and VPC with a SFC-R. None of these combinations changed the results at all; it was as if the OBD1 computer was ignoring the MAF reading and staying in closed loop! Weird shit....

This was with a stock '94 ECU. Same results when I tried it with a different OBD1 ECU, this one being a EuroX modified ECU.

Then I put the '98 ECU back in, didn't change anythign else, and EGTs were back to maxing out at 650-660C at the end of a long pull.

I guess my '98 is one of the few that really just doesn't like OBD1 ECU's.... and my guess is that Scott Smith's '98 is another...

Andi

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The Pikey

· #8 · Sep 19, 2001

Andi said:
650C is okay. That means your car is running pretty close to optimal IMHO.. (I'm assuming the 650C is at the end of a long pull to 150mph, not a short 3rd gear blast to 90 or a 4th gear romp to 120)...

Back when I had an OBD1 ECU, I could easily see 700C by the end of a 40 to 120 pull. The wideband o2 said I was running 13:1. Not cool. FYI I tried 4 different combinations with the same results: MAF with no fuel computer, S-AFC with MAF, VPC by itself, and VPC with a SFC-R. None of these combinations changed the results at all; it was as if the OBD1 computer was ignoring the MAF reading and staying in closed loop! Weird shit.... This was with a stock '94 ECU. Same results when I tried it with a different OBD1 ECU, this one being a EuroX modified ECU.

Then I put the '98 ECU back in, didn't change anythign else, and EGTs were back to maxing out at 650-660C at the end of a long pull.

I guess my '98 is one of the few that really just doesn't like OBD1 ECU's.... and my guess is that Scott Smith's '98 is another...

Andi

Don't Jinx me Andi

I'll know at 4pm today if this is true.

Scott

Peace

Steve Jarvis

· #9 · Sep 19, 2001

I changed my 97 ecu for a 95 ecu and it's a different car. It idles a little higher (about 500rpm) and much smoother. M car used to miss just a little bit when shifting from 2nd to 3rd. It acted as if the traction control was still on even though I had it switched off. After changing to the 95 ecu, it "barks" the tires 95% of the time on a hard shift from 2nd to 3rd. This car had the ignition timing advanced and the fuel leaned out. It made 438rwhp on pump gas through the stock MAF. I reset all the settings to 0 and the car did feel down on power. After I put the 95 ecu in it felt as if all the power had returned and all the aftermarket fuel and timing computers were still at 0. And of course it got rid of all those check engine lights. If I tried to start the car in TTC mode with the ETTC mod, the check engine light would always come on. It does disable your traction control and cause the light to flash, but I always had the trac fuse pulled on my 95 and removing the bulb got rid of the flashing light.

Later, Steve

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G

· #10 · Sep 19, 2001

Andi,

The highest I've taken the car is ~120mph when finishing the 1/4 mile. The 1200F reading was the peak value reached during those runs.

I guess I'll find out more once I install an aftermarket fuel control system. Most likely I'm going to purchase a VPC/GCC combo.

I have noticed the car idles higher on cold starts compared to the OBDII ECU, but settles down to normal once at full operating temperature.

I'll try a pull tonight running through the gears and see what I come up with just to make sure my memory is serving me correctly.

Grant

· #11 · Sep 19, 2001

1200F sounds high to me. Thats 649C. The highest I see at the end of the 1/4 is 600C on my GReddy gauge. And that was with the car a leaned out a tad too much and some timing retard (About 1 degree). I'd shoot for 580-590 at the end of the 1/4, but tuning via EGTs is probably a very bad idea.

Of course on the street, with the probe in the DP heat soak plays a huge roll. I'll see 640C at the end of 4th if the car had been left at a high RPM prior to the run. IMO the only use of an EGT gauge is to tell you if something is wrong, you can't really tune by it.

Andi

· #12 · Sep 19, 2001

Grant,

FYI my best runs in the 1/4 (121mph) were with a peak EGT of 620C.

And trying to find out if something is wrong by using EGT is exactly what we're doing here.... not tuning, just seeing if the car likes the ECU...

Andi

G

· #13 · Sep 20, 2001

Here are the results from my run tonight:

Started in [email protected] - 825F(426C).
Top of 4th - 1175F(621C)
Mid 5th - 1225F(649C).

I stayed in 5th for ~3 seconds. Don't ask me mph because I was too busy watching the road! I've only got country roads to do this on!

Andi

· #14 · Sep 20, 2001

QuikSilverTT said:
Here are the results from my run tonight:

Started in [email protected] - 825F(426C).
Top of 4th - 1175F(621C)
Mid 5th - 1225F(649C).

I stayed in 5th for ~4 seconds. Don't ask me mph because I was too busy watching the road! I've only got country roads to do this on!

Sounds like your car is tuned ok.

Andi

G

· #15 · Sep 20, 2001

Andi,

Too bad we live so far from each other. I would like to try my OBDI ECU in your car to see what the results would be. Strange that it works in my car but not yours or Scott's.

Unfortunately I don't have a BCC, otherwise I'd try my OBDII ECU to compare the results.

I don't know if this matters, but my peak boost was in 5th @18psi. Mostly 16-17psi throughout most of the run.

G

· #16 · Sep 20, 2001

guys,

see if you can help me out a bit on my EGT situation.
I am 94 BPU running 18psi on stock MAF and stock fuel and FMIC. recently after I installed my Omori EGT gauge with probe on top of DP, I have been geting EGT reading up to 750C

on a hard pull to 130+ on 5th gear.
I know its running way too hot, can you guys help me identify what could be the problem?
I just ordered the HKS AFR hoping to dial more fuel into the engine and make it run extra rich, other than that I am suspecting the problem originates from our shitty california 91 octan pump gas.
Also, my fuel filter was changed around 20,000miles ago.

thanx

Jonas

Andi

· #17 · Sep 20, 2001

Zerosoul said:
guys,

see if you can help me out a bit on my EGT situation.
I am 94 BPU running 18psi on stock MAF and stock fuel and FMIC. recently after I installed my Omori EGT gauge with probe on top of DP, I have been geting EGT reading up to 750C on a hard pull to 130+ on 5th gear.
I know its running way too hot, can you guys help me identify what could be the problem?
I just ordered the HKS AFR hoping to dial more fuel into the engine and make it run extra rich, other than that I am suspecting the problem originates from our shitty california 91 octan pump gas.
Also, my fuel filter was changed around 20,000miles ago.

thanx

Jonas

that's hot! WAY too hot! When Mohd had the same problem as you, he found out his fuel pressure regulator was bad.... I'd replace that first.. the FPR is crucial to getting the fuel pressure increase with boost.... w/o it you can run lean the way you are, so that'd be my first supicion.... then, also change the fuel filter, and possibly install a fuel pressure damper bypass (Jarrett at Powerhouse sells these now)...

Andi

G

· #18 · Sep 21, 2001

Andi, read your bio, you received your Masters degree when you're 18?! wow, smart dude....thanx for helping out on my EGt problem. gonna have fuel filter replaced, HKS AFR installed, and aftermarket FPR installed next weekend, hope it will solve my EGT problem.

Jonas

G

· #19 · Sep 21, 2001

QuikSilverTT said:
Here are the results from my run tonight:

Started in [email protected] - 825F(426C).
Top of 4th - 1175F(621C)
Mid 5th - 1225F(649C).

I stayed in 5th for ~3 seconds. Don't ask me mph because I was too busy watching the road! I've only got country roads to do this on!

Looks like I have some calculation errors.

825F = 441C
1175F = 635C
1225F = 663C

Sorry.

G

· #20 · Jan 29, 2002

do you guys think by doing ECU upgrade (ex. G-Force upgrade)
it would solve this close loop problem?

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