Bonestocks 88GT 3800sc w/ Getrag swap

Series8217 · Post by **Series8217** » Fri Oct 10, 2008 6:13 pm

For the idle problem:

The ECM will not command the IAC until it sees 0% throttle position from the TPS. The ECM determines where 0% throttle is by recording the LOWEST voltage it has seen from the TPS that isn't 0.00volts. The highest voltage it has seen is also recorded, and this is 100% throttle. This way the ECM can adapt to sensors that may have slightly offset resistances.
Anyway, if one or more of your TPS wires or connections along the way are not perfect, sometimes the voltage will drop slightly when the wires vibrate, and the ECM will record the new low voltage... but then the voltage bounces back up to the original value and now the ECM thinks you're at like 5% throttle.
Since this is happening right at startup, it's probably a ground fault or a problem with the reference voltage. When you're cranking your motor the voltage is probably getting pulled down a bit, and the ECM is recording it as the zero position.

Both Blue Shift and I had this problem with our DOHCs.. seems to be pretty common.

Bonestock · Post by **Bonestock** » Fri Oct 10, 2008 8:17 pm

Series8217 wrote:For the idle problem:

The ECM will not command the IAC until it sees 0% throttle position from the TPS. The ECM determines where 0% throttle is by recording the LOWEST voltage it has seen from the TPS that isn't 0.00volts. The highest voltage it has seen is also recorded, and this is 100% throttle. This way the ECM can adapt to sensors that may have slightly offset resistances.
Anyway, if one or more of your TPS wires or connections along the way are not perfect, sometimes the voltage will drop slightly when the wires vibrate, and the ECM will record the new low voltage... but then the voltage bounces back up to the original value and now the ECM thinks you're at like 5% throttle.
Since this is happening right at startup, it's probably a ground fault or a problem with the reference voltage. When you're cranking your motor the voltage is probably getting pulled down a bit, and the ECM is recording it as the zero position.

Both Blue Shift and I had this problem with our DOHCs.. seems to be pretty common.

I dont know then because my wiring harness is an Injection Technology one and thats all new and not spliced together. I hope its just a faulty sensor. I am going to pick and pull and grab a few since 3800 na and sc are the same.

darkhorizon · Post by **darkhorizon** » Sat Oct 11, 2008 12:55 am

You could try a TPS relearn, its easy and only takes a min.

foot off pedal, key on, 10 seconds, key off
pedal to the floor (ensure WOT at throttle body), key on, 10 seconds, key off

Repeat 4 times.

Exhaust looks real good, simple quick, cheap, high flow, should perform well.

Series8217 · Post by **Series8217** » Sat Oct 11, 2008 3:03 am

I've seen off-the-shelf harnesses that are miswired. You might want to double check the wiring for that circuit and make sure its not putting 12 volts or something equally wrong for the TPS reference voltage. Also make sure the sensor ground is actually going to the ECM pin for it, and not something on the chassis or engine..

darkhorizon wrote:You could try a TPS relearn, its easy and only takes a min.

foot off pedal, key on, 10 seconds, key off
pedal to the floor (ensure WOT at throttle body), key on, 10 seconds, key off

Repeat 4 times.

Same effect by just disconnecting the TPS which he has already done. When the ECM sees 0.00 volts from the TPS, it sets an error code. When it sees a non-zero voltage again, it resets its TPS values and starts over..

Bonestock · Post by **Bonestock** » Sat Oct 11, 2008 3:47 am

Just a few things to sort about the harness. Jim didnt pin the CEL so I have to go in and add a wire. He is used to making Ed Parks 4.9 harness and they leave the CEL out for some reason. Also my trunk release has stopped working. I can hear the relay under the dash click but nothing happens. I need to spend some time and figure that one out.

Series8217 · Post by **Series8217** » Sat Oct 11, 2008 3:58 am

This may sound stupid, but are you testing it with the decklid closed? It has to be closed so the solenoid can ground through it. This has fooled me both times I've swapped regular latches to power latches... first test I was scratching my head wondering why I was getting power but the solenoid wasn't firing.
The circuit is pretty simple, the output from the relay goes straight to the solenoid. The next connection after the relay connector is the weatherpack connector going to the decklid; I doubt anything is busted between it and the relay.. but the weatherpack connector often gets heavily damaged from engine bay heat and starts to fall apart when manipulated. The terminals also get corroded especially if left open. You may need to repin it.

darkhorizon · Post by **darkhorizon** » Sat Oct 11, 2008 9:58 am

Series8217 wrote:I've seen off-the-shelf harnesses that are miswired.
Same effect by just disconnecting the TPS which he has already done. When the ECM sees 0.00 volts from the TPS, it sets an error code. When it sees a non-zero voltage again, it resets its TPS values and starts over..

I think you are mistakeing it for something else..

The relearn sets what 0% and 100% are according to the pcm... on his car .034v might be fully closed, and on others it might be .037.. so it just takes that variance out and sets whatever his fully closed voltage is as 0% tps.

Series8217 · Post by **Series8217** » Sat Oct 11, 2008 2:20 pm

darkhorizon wrote:
Series8217 wrote:I've seen off-the-shelf harnesses that are miswired.
Same effect by just disconnecting the TPS which he has already done. When the ECM sees 0.00 volts from the TPS, it sets an error code. When it sees a non-zero voltage again, it resets its TPS values and starts over..
I think you are mistakeing it for something else..

The relearn sets what 0% and 100% are according to the pcm... on his car .034v might be fully closed, and on others it might be .037.. so it just takes that variance out and sets whatever his fully closed voltage is as 0% tps.

Excuse me? Did you read my post?

The ECM will not command the IAC until it sees 0% throttle position from the TPS. The ECM determines where 0% throttle is by recording the LOWEST voltage it has seen from the TPS that isn't 0.00volts. The highest voltage it has seen is also recorded, and this is 100% throttle. This way the ECM can adapt to sensors that may have slightly offset resistances.
Anyway, if one or more of your TPS wires or connections along the way are not perfect, sometimes the voltage will drop slightly when the wires vibrate, and the ECM will record the new low voltage... but then the voltage bounces back up to the original value and now the ECM thinks you're at like 5% throttle.

I know how it works. I've looked at the actual software code. Disconnecting the TPS sets a TPS low voltage error which unsets a flag so the ECM will re-determine the TPS range when it sees a non-error voltage again.

Bonestock · Post by **Bonestock** » Sun Oct 12, 2008 3:04 am

Did a little diagnostic work but nothing solved the high idle problem.

Swapped 3 different TPS- all ranged to 4.5v full throttle but the lowest at closed was .98v.

Swapped MAF- no change

Swapped original PCM- no change

Wiggled wire at C500 and the trunk release worked for a bit- HMmmm may be on to something here.

Tried TPS reset- idled at 500rpm and sounded like a diesel tractor going to explode.

Fumes from the exhaust were so strong in my garage (even with the door up and fan on) burnt my eyes.

Unplugging the TPS once running and let the idle settle to 900rpm and replugging it still solves the high idle until you turn the car off.

Noticed a bit of a hesitation/stumble at part throttle on my 20 min trip tonight... fuck, not that again.

Still didnt get to hook the MODEUS to it. Will do that tomorrow.

Put some fresh 93 octane in it since it was filled with 87. Man it pulled MUCH better.

Series8217 · Post by **Series8217** » Sun Oct 12, 2008 3:27 am

That's weird that the C500 would affect the trunk solenoid. The solenoid wire doesn't go through a connection there; it branches off of the bundle of wires for the chassis harness before they reach the C500.

Are you using a scanner to watch the ECM datastream or just measuring the TPS voltage with a multimeter?

darkhorizon · Post by **darkhorizon** » Sun Oct 12, 2008 4:38 am

Put some fresh 93 octane in it since it was filled with 87. Man it pulled MUCH better.

How could you tell? If you actually romped on it wide open with 87 in there... and no tune as it is... I wouldnt even want to know what sort of KR you were seeing.

Bonestock · Post by **Bonestock** » Sun Oct 12, 2008 7:17 am

Trunk release does go throught the C500, B1 IIRC.

Dark, the PCM was tuned by Brunton Automotive, they are the makers of the Stalkerv6 kit car here in Fl. I was quoted to have about 250-260whp. It starting to feel that way once I put good fuel in it.

The Dark Side of Will · Sun Oct 12, 2008 8:46 am

Bonestock wrote:Trunk release does go throught the C500, B1 IIRC.

Not according to the '88 shop manual. The solenoid power comes from the CTSY/LID fuse, goes through the switch and the secondary of a relay. The relay primary is energized by the parking brake switch in manual cars and the transmission range selector switch in automatic cars. In automatic cars, the wire passes through C500-A4... but that's your crank wire. If you have problems with that, your car wouldn't start.

The supply to the trunk release is the CTSY/LID fuse which is supplied by fusible link A right from the battery junction block *next to* the C500 connector.

Series8217 · Post by **Series8217** » Sun Oct 12, 2008 2:47 pm

Bonestock wrote:Trunk release does go throught the C500, B1 IIRC.

It will not go there if you have a manual transmission. Did/do you have an automatic? If so, you have to change the wiring in your car. The chassis harnesses are different. You need to remove the big yellow wire going to the relay, and replace that terminal connection with a splice to the brake warning system wire going to the steering column. It's tan with black stripe if I remember correctly. Check the wiring diagram.

I guess for the automatic, the selector switch grounds the solenoid wire when you're in park or neutral, thus providing a ground path for the relay. With a manual transmission, the e-brake switch is used instead. When the e-brake is applied, the switch on the handle provides a ground path for the "BRAKE" light in the instrument cluster. This is used as the ground path for the trunk release relay.

Bonestock · Post by **Bonestock** » Sun Oct 12, 2008 3:10 pm

The Dark Side of Will wrote:
Bonestock wrote:Trunk release does go throught the C500, B1 IIRC.
Not according to the '88 shop manual. The solenoid power comes from the CTSY/LID fuse, goes through the switch and the secondary of a relay. The relay primary is energized by the parking brake switch in manual cars and the transmission range selector switch in automatic cars. In automatic cars, the wire passes through C500-A4... but that's your crank wire. If you have problems with that, your car wouldn't start.

The supply to the trunk release is the CTSY/LID fuse which is supplied by fusible link A right from the battery junction block *next to* the C500 connector.

Got ya. Yeah my car is and always has been a manual. So I wonder why my brake light will flicker when I hit the release and it doesnt pop?

Bonestock · Post by **Bonestock** » Sun Oct 12, 2008 9:36 pm

Codes:
P0753
P0123
P0132
P0502
P0121
P0140
P0530
P1673

darkhorizon · Post by **darkhorizon** » Mon Oct 13, 2008 4:51 pm

Codes:
P0753 - transmissin = programming error
P0123 - TPS = wiring issue
P0132 - O2 b1s1 = wiring issue
P0502 - vss = wiring issue
P0121 - tps = wiring issue
P0140 - rear o2 = programming error
P0530 - air conditioning pressure = programming error if you specified no ac, or wiring issue if you have it.
P1673 - engine temp idiot light = bad wiring, you should have this

Thats one TERRIBLE wiring harness job, thats at least 5 errors right there!

Who did the tune on the pcm? They did a horrid job on that too!

Bonestock · Post by **Bonestock** » Mon Oct 13, 2008 7:13 pm

Actually before you start ripping into people you should wait and see what the problems are.

We found that I somehow forgot to plug in the front 02 sensor while adding plug wires! Sweet! I knocked the vac line off the MAP as well. We got those sorted and the car starts and idles fine 60% of the time. For some reason we can get 100% throttle angle and 4.5v @ WOT but can NOT get throttle position to less than 15% or 1.2v @ idle.

I need to talk with Brunton about a few of the other codes because they were suppose to shut off the rear 02, and any auto trans codes etc.
The a/c one is there simply because I dont have the system connected and charged yet.

Series8217 · Post by **Series8217** » Mon Oct 27, 2008 4:03 am

So you gave up on the swap or what?
I heard you sold the car.

MstangsBware · Post by **MstangsBware** » Mon Oct 27, 2008 10:27 pm

Series8217 wrote:So you gave up on the swap or what?
I heard you sold the car.

Feel sorry for whoever buys the car. Like most swaps there are bugs that need to be worked out as miles get put on the car. This car was thrown together and then SOLD. I hope the buyer is close by so the seller can help when the issues start to come up.