• Dave
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  • From: PGH PA
  • Registered: 2009-10-09
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Topic: HELP with Fooling OBDII Computers

The stork just dropped a crashed 1998 Olds 88 3.8L(vin K) Supercharged at our parking lot. (I have the best customers!) We need help with fooling the PCM into believing the transmission is in drive and the downstream O2 is working correctly. The motor will be mated to a manual transmission, and there will be NO downstream O2. (Cat) I am pretty good with OE stuff but aftermarket I'm in the dark. Any help would be greatly appreciated. big_smile
                  Dave

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  • From: Mentor, OH
  • Registered: 2010-02-22
  • Posts: 207

Re: HELP with Fooling OBDII Computers

Search ebay/google for the correct resistor to put in the wiring for the O2 sensor.  They sell these all the time for the LS1 guys.  As far as fooling the tranny, you may need to check the wiring while the car is in drive and see what kind of signal the computer is receiving and then try to duplicate that.

Maybe try to swap the harness and ecu over to the pre 96 version?

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3 Reply by EyeMWing (edited by EyeMWing 2010-10-29 07:03 AM)

  • From: Baltimore, MD
  • Registered: 2010-05-20
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Re: HELP with Fooling OBDII Computers

The downstream O2 is easy - you can buy one (zzperformance.com has one from what I recall - check under Grand Prix) or, even better, you can just ignore it. It has no effect on anything except the cute little lightbulb.

The trans, not so much. That's going to be a wiring diagram job (I don't have time to look now, unfortunately) - your best bet is going to be to take your Olds diagram and compare it to a diagram for a Holden VX Commodore. Bastard Aussies got the engine mounted the proper way around and with a manual transmission and everything.

I can't wait to see what the hell you're going to put that motor in and will need to track you down and talk shop when it shows up on the track.

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  • From: Gilbertsville, PA
  • Registered: 2009-12-22
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Re: HELP with Fooling OBDII Computers

I think stuff can be programmed out w/ EFI live software and a few others that I'm not thinking of right now.

Most Dyno shops either have this software or they'll know who has it.  Then you could sweet talk your way around whatever fee they'd charge to do it for you.

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  • BoB
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Re: HELP with Fooling OBDII Computers

I know some people swap out the ecu's in the olds for one out of something a little sportier like the grand prix.  They typically do it since the grand prix had a tune with a bit more power.  If you find one with a manual trans and take the ecu from that car it might save you some trouble.

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  • From: Safety Harbor, FL (Tampa)
  • Registered: 2009-04-30
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Re: HELP with Fooling OBDII Computers

As for the O2, most ECU's (probably all on cars that are of typical Lemons vintage) only use the O2 for warm idle and cruise.  When the engine is cold, it doesn't use the O2 feedback, and when you're WOT, it doesn't use the feedback.  So, for racing, ignore the CEL and don't worry about the O2 sensor.  When you're full throttle, it's not going to matter.

To get past the transmission thing, I like the "switch to a manual ECU" idea.  Though there's probably some simple switch in the auto trans that you could simulate with a jumper wire.

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7 Reply by Team Infinniti (edited by Team Infinniti 2010-10-29 02:27 PM)

  • From: WPB Fl.
  • Registered: 2010-10-27
  • Posts: 1,571

Re: HELP with Fooling OBDII Computers

Really simple, unbolt the neutral safety /range switch and leave it plugged in(placed in the correct range) then tie it up to keep it safe, if you loose it the computer will limit revs to 4000 or so. Do the same to the downstream o2 sensor if you like but it is not needed as the computer uses the upstream sensor for all mixture decisions. Downstream sensors are only there to monitor catalyst efficiency.

You better check that VIN code (k)  is the 3.8 WITHOUT the supercharger, you want to see a VIN code (1) to get the 40 extra pony's .

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8 Reply by DaveH (edited by DaveH 2010-10-29 02:55 PM)

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Re: HELP with Fooling OBDII Computers

Do it right.  Search around the web, you can ship off your ECU and have it reflashed for less than $100.  Then there's no wiring or resistors to deal with.  The newer cars with electronically controlled transmissions are hard to fool.  Generally if you talk to the shop and let them know exactly what you're doing with it they can do a custom flash and turn off what needs to be turned off.  (Bonus, extra power!)

Also, if your speed sensor from the trans isn't compatible with the ECU (or didn't exist) it will cause problems.  Get aftermarket ones here:

http://www.dakotadigital.com/index.cfm/ … prd109.htm

If the car didn't have an 8000 pulse per mile sensor (I think nearly all GMs do), it can be reflashed to be compatible.  Again, let the reflash shop know what you're installing.

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Re: HELP with Fooling OBDII Computers

totally different car obviously but we just shorted the leads to the neutral safety switch on our 240sx. works like a champ.

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  • From: Baltimore, MD
  • Registered: 2010-05-20
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Re: HELP with Fooling OBDII Computers

BoB wrote:

find one with a manual trans and take the ecu from that car it might save you some trouble.

Not a single car was sold in the US with that engine and a manual transmission. NONE. The only ECUs preloaded for use with a manual trans are going to have to come from Australia.

I'm almost certain that, other than the neutral safety switch, there is no output from the transmission to the ECU, meaning you can just unbolt the damned transmission, fake the neutral safety switch, and have a grand 'ol time - but that comes with a huge "I'm drunk off my face and the lines on this diagram are blurrrrryyyyy" disclaimer until tomorrow.

If I remember I posted this tomorrow.

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  • From: Santa Margarita, CA
  • Registered: 2009-06-03
  • Posts: 177

Re: HELP with Fooling OBDII Computers

Be glad its not a really new OBDII (+canbus) car as the transmission and engine have a chat about torque requests and tons of shit.

Regarding the oxygen sensor, I don't even run it. ECU is so ancient (89) that it only uses it for cruise and being an unheated unit means its not used for idle.

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  • From: Gilbertsville, PA
  • Registered: 2009-12-22
  • Posts: 3,251

Re: HELP with Fooling OBDII Computers

djcommie wrote:

Be glad its not a really new OBDII (+canbus) car as the transmission and engine have a chat about torque requests and tons of shit.

Regarding the oxygen sensor, I don't even run it. ECU is so ancient (89) that it only uses it for cruise and being an unheated unit means its not used for idle.

98 and up fbodies have torque management too.

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  • From: St Louis, MO
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Re: HELP with Fooling OBDII Computers

I heard about some guy trying to convert his 3.8 Olds (I think, or maybe it was a Bonneville) to a manual. Far as I know he gave the project up. I'm not even sure if the 3800 was paired with a manual in Australia, here in the F body it was still stuck with an automatic. While I'm sure a swap would be possible given enough time and money, I don't know if it could be done on a Lemons budget or if it'd be reliable.

How banged up is the Olds? If it's salvageable I'd patch it back together and run it as is.

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  • From: Baltimore, MD
  • Registered: 2010-05-20
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Re: HELP with Fooling OBDII Computers

Yeah, just verified (sober-style) that the transmission itself is only outputting to the PCM via a temperature sensor. I don't know what the hell it'll do if it doesn't receive a temperature (probably throw another code you can ignore - it's the yellow/blk line from the ECU if you want to tap it and analyze it to produce a convincing fake)

Everything else is an output from the ECU to solenoids and a pressure valve override switch (probably for the paddle shifter kit). Other than that, you just have to fake the neutral safety switch. Let me know if you want me to email you the diagram.

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Re: HELP with Fooling OBDII Computers

Alright here is what I know about OBDII at this moment in time (I'm sure I've forgotten more than I can remember) The goal is to have the air flow ratio meet the magic 14.7 to 1 (statiometric) The PCM takes the information from various sensors such as but not limited to, engine coolant temp, air temp,manifold vacuum, air density(flow)Knock sensor,up & down stream o2, vss & rpm. When a sensor is missing or malfunctioning the PCM will "look" at the the other sensors and substitute a "value"that it should be and then turn on THE LIGHT. When operating correctly and the PCM recognizes a load put of the engine it will richen up the a/f mixture and adjust the timing to compensate for the load.
On this OLDS the PCM also takes input from the transmission & BCM I have contacted a PCM reprogramer who claims they can help me out. I will send out the PCM  later this week. I should have the project up and running by the first of the year. Thanks for all the help & suggestions. I will keep every one posted as work progresses.
         Thanks again, Dave 


PS. How about a Supercharged Bradley GT wink

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  • From: Mentor, Ohio
  • Registered: 2010-04-19
  • Posts: 208

Re: HELP with Fooling OBDII Computers

Dave wrote:

PS. How about a Supercharged Bradley GT wink

YES!

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  • From: Gilbertsville, PA
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Re: HELP with Fooling OBDII Computers

What could possibly go wrong?

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Re: HELP with Fooling OBDII Computers

rpone605 wrote:
Dave wrote:

PS. How about a Supercharged Bradley GT wink

YES!

Absolutly!

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Re: HELP with Fooling OBDII Computers

Team Infinniti wrote:

Really simple, unbolt the neutral safety /range switch and leave it plugged in(placed in the correct range) then tie it up to keep it safe, if you loose it the computer will limit revs to 4000 or so. Do the same to the downstream o2 sensor if you like but it is not needed as the computer uses the upstream sensor for all mixture decisions. Downstream sensors are only there to monitor catalyst efficiency.

You better check that VIN code (k)  is the 3.8 WITHOUT the supercharger, you want to see a VIN code (1) to get the 40 extra pony's .

Best solution.