94 Trans Sport 3.8 no power, stalls...

My 94 Trans Sport has 150,000 miles on it and the current problem is it Idles high ~1800-2000, will not rev past 3800-4000 (acts like a rev limiter) and occasionally stalls at traffic lights, stop signs and some times when just letting off the gas at slow speeds. Just changed the plugs so they are new...ignition wires are about 60K old so probably need to be replaced as well. I'm thinking IAC from what I have read. The CEL is on but I have not had the codes read...my Haynes manual says I can access the codes by jumpering some terminals on the connector under the dash and viewing a sequence of flashing light on the dash. The problem is the concoctor does not match the one in the book and doesn't appear to have pins in the numbers they say to jump together.

Any suggestions?

Thanks,
Scott

.. I'm thinking IAC from what I have read. ......connector doesn't appear to have pins in the numbers they say ...

Yes IAC can be a problem but the drive from the computer can be too; may be some sensor is flawed and computer does not control correctly.
... about the RPM limiter, that is a fact.
Flashing the codes needs pins A and B.
http://www.avigex.ca/xport/plug.jpg; I think early '94 still had that configuration then changed and then it needs a scanner.

Yes IAC can be a problem but the drive from the computer can be too; may be some sensor is flawed and computer does not control correctly.
... about the RPM limiter, that is a fact.
Flashing the codes needs pins A and B.
http://www.avigex.ca/xport/plug.jpg; I think early '94 still had that configuration then changed and then it needs a scanner.

I pulled the IAC and it was real dirty and out of adjustment...manual calls for 1.125" from the mounting base to the tip of the pintle...it was 1.250". I adjusted it to 1.125", cleaned it and reinstalled. The idle was noticably better and more steady at ~900-1000 rpm but still stalls from time to time and still doesn't seem to have very much power...guessing the IAC is bad since it improved with the cleaning. Also thinking the throttle body may be real dirty as well considering how dirty (carboned up) the IAC was.

Now for the SEL and code issue...mine does not have the above pictured pinout on the ALDL, there is no pin in the "B" location...manufacture date on the door jam sticker is 03/94. I have a AutoXray XP240 scanner that I barrowed from a friend. It is not reading the data...keep getting "no engine data" ?

Any sugestions?

Thanks,
Scott

The 94-95 U Vans with the 3800 used the OBD1 Protocol but it used the OBD2 codes.... You could call it the Pre OBD2 PCM... We call it the Hybrid OBD1.5...And yes the Diagnostic pin is no longer in the ALDL for these vehicles..

You have to have a Scan Tool that is capable of reading the 94-95 Vin L's..

Does you van simply stall at random? No reason no rhyme? And when it does this will it restart every time? While you are roling along do the gages freak out before or when this happens?

Also if you can read the codes or get them read look for any code such as

P01361

Or

P0361 ....

The 94-95 U Vans with the 3800 used the OBD1 Protocol but it used the OBD2 codes.... You could call it the Pre OBD2 PCM... We call it the Hybrid OBD1.5...And yes the Diagnostic pin is no longer in the ALDL for these vehicles..

You have to have a Scan Tool that is capable of reading the 94-95 Vin L's..

Does you van simply stall at random? No reason no rhyme? And when it does this will it restart every time? While you are roling along do the gages freak out before or when this happens?

Also if you can read the codes or get them read look for any code such as

P01361

Or

P0361 ....

Yes it just stalls and then it will start back up...usually when I stop at light or even slow way down to turn into a parking lot for example. Never noticed the gages acting up.

The scanner I have does ask for the vin 8th number and "L" is an option. Tried it on '94 but not sure if I tried it for '95...did not read data for '94.

Just for a test, disconnect the plug from the EGR valve and run the car. . Some of the symptoms you describe are typical of failed EGR valve operation, which is a common failure at that age. It is quite possible the codes you are unable to read come from that unit. Report the results.
http://www.avigex.ca/xport/egrlin.jpg

I'll give that a try...will a bad EGR kill the power as well?

thanks

I'll give that a try...will a bad EGR kill the power as well?

thanks

I agree with LMP you can unplug the EGR and see if runs any better...

It depends on weather or not the EGR is Open when commanded closed... You have to have a certain engine Temp, Have the engine in gear and have Load( Via TPS ).... At that point it will actuate the EGR... If it runs better with it unplugged then you may have found your issue..

At the same time, Have you checked all of the Vac lines to the top of the intake plenum?

Ok...pulled the PCV, don't know if it has ever been changed, I didn't have a new one handy so I just cleaned it for now...didn't really make a difference.

I unplugged the EGR...no change. The scanner I mentioned earlier set to both '94 and '95 vin "L" I get "no engine data" on the display. I seems to idle smoth and rev smooth but if you rev it up quick and let off it will stall out every time when the throttle returns back to its starting position...still stalls while driving...mostly when slowing down to turn or stop. Idle goes up and down from 2000 rpm to 1500 rpm and sometimes drops to 800-1000 rpm but usually doesn't stay. The idle improved breifly when I cleaned the IAC.

no what...replace the IAC, why won't my scanner work ?

also checked the vaccum lines but seemed to be ok...

The more you describe the more I think that the TPS sensor may be at fault.... But its hard to say without the data to back it up..

On the Scan Tool, Does it have coverage for the 94-95 3800 Transport?

I read my 95 Bonne and Transport with my Old Actron CP9110 and the GM card and 12 Pin ALDL cable( OBD 2 Cable for the 95 Bonneville, Just a different connector, exact same PCM )... Never have any issues viewing codes or data..

If there is anything else we can help you answer please let us know:smile:

The scanner I have "AutoXray XP240" only asks for GM, Ford or Crysler, the year and the 8th vin when I enter '94 or '95. I enter: GM, '94 and VIN "L"...same with '95. Guess I'll have to find another scanner ?

Shouldn't I be able to test the TPS with a volt meter ?

Thanks,
Scott

Not sure why the Scanner will not read the van...

Yes you should be able to test the TPS...

iirc it should be between .36-.42 or so close throttle plate... And should be 4.5 or so at Wide open throttle..

You should fall near or within the ranges, as you open the throttle plate slowly the numbers should go up and in a smooth manner, if you have any sudden drop out then I would say the TPS is not happy.. Let us know what you find:smile:


And being curious, have you checked for Vac leaks? These engine get very unhappy if they get any air that has not gone by the MAF as there is more air there then the PCM has determined to be there and this can cause issue with idle and stalling as well.... Just more for you to check out while you are there..

So I finally found a scanner that will work. I picked up from Amazon.com a Actron CP9145 Super Auto Scanner $99, GM ALDL cable kit CP9127 $23 and hard shell carry case $28 (free shipping) then minus a 1st time purchase on Amazon Visa $30 rebate for a total of $120. Best deal I could find...all brand new in the box.

I started the van up...haven't started it for about 3-4 weeks and it goes to high idle ~2500-3000 rpm (would not kick down) then after about 5-10 min. it dropped down to ~800-900 rpm. I hooked up the scanner and read the codes...this is what I got:

Current Code P0401
Linear EGR Flow Failure (DTC lookup EGR Flow Insufficient)
Current Code P0640
Quad Driver Module, QDM 1 Fault (DTC Lookup Intake Air Heater Control Circuit)
Current Code P0670
Quad Driver Module, QDM 4 Fault (DTC Lookup Glow Plug/Heater Module Control)
History Code P0123
Throttle Possition Sensor (TPS) Signal High (DTC Lookup TPS/Pedal Position Sensor A Circuit High Input)
History Code P0406
Linear EGR Pintle Position, Position Error (DTC Lookup EGR Flow Sensor A Circuit High Input)

Guessing the last 2 were from when it was stuck on high idle when I started it up and then went away when the idle finally kicked down.

I then cleared all codes with the scanner and read the codes again...the SEL went off shortly but then came back on. Idle was normal...EGR and TPS errors are gone. These codes returned...

Current Code P0640
Quad Driver Module, QDM 1 Fault (DTC Lookup Intake Air Heater Control Circuit)
Current Code P0670
Quad Driver Module, QDM 4 Fault (DTC Lookup Glow Plug/Heater Module Control)

So now what...what is the Quad Driver Module ?

Thanks,
Scott

I'll have to do a little more digging to see what is on the QDM circuits... If there is an issue with anything on those QDM circuits then you can set the codes when it see a problem with an actuator...

so we need to figure out why those codes are there..

Does this Van have the 3800? Or is it the 3.1?

I'll look more into this for you... If I forget Please drop me a PM..

QUad driver faults just says the voltage condition at driver output is out of normal range. Drivers (grouped in pack of four in a single module, hence QUAD) are transistor acting as switches that are used to ground a circuit fed by 12V . Voltage condition at driver is high (12V) when circuit is unenergized hence not grounded, and falls to near ground voltage, like 0.5 V, when driver is energized.

so..either the circuit (generally a solenoid coil) tied to the unergized driver is open and no 12V is seen at driver input

or driver is "thought" to be energized hemce voltage should be 0.5V, and driver transistor is shot (rare..in fact almost unheard of) and does not ground the circuit, hence voltage stays high.

QDM error does not tell the driver is faulty, just that the voltage condition read at QDM is not what it should.THe first condition is generally the one that prevails in most faults .

BOth definitions for the codes you have are mindboggling though. THe only "heater" I see in this engine is the O2 sensor heater.....but other codes would reveal that in a more explicit way...and this would not act on a cold engine idle...

Drivers are used to control the step motor that sets Idle (Idle AIr Valve) ....I'd be tempted to look in that direction. www.avigex.ca/xport/fuelcontrol_iac.jpg Faulty air idle valve operation could cause high idles as well as stalls ...
ALso notice that vacuum leaks cause high idle.

I have the 3.8 by the way if you didn't figure that out :wink:

If you remember back in my earlier post I cleaned the IAC and had to adjust it since it was pretty far out of adjustment...it did improve but was only short lived. The EGR was replaced a few years ago, the IAC has never been replaced...maybe it's time. Not too expensive and couldn't hurt even if it's not the main problem. Somthing hangs up in the idle control when it is 1st started after sitting a long while but usually frees up after 5-10 minutes but still is not 100% and will still occasionally stall.

Thanks,
Scott


QUad driver faults just says the voltage condition at driver output is out of normal range. Drivers (grouped in pack of four in a single module, hence QUAD) are transistor acting as switches that are used to ground a circuit fed by 12V . Voltage condition at driver is high (12V) when circuit is unenergized hence not grounded, and falls to near ground voltage, like 0.5 V, when driver is energized.

so..either the circuit (generally a solenoid coil) tied to the unergized driver is open and no 12V is seen at driver input

or driver is "thought" to be energized hemce voltage should be 0.5V, and driver transistor is shot (rare..in fact almost unheard of) and does not ground the circuit, hence voltage stays high.

QDM error does not tell the driver is faulty, just that the voltage condition read at QDM is not what it should.THe first condition is generally the one that prevails in most faults .

BOth definitions for the codes you have are mindboggling though. THe only "heater" I see in this engine is the O2 sensor heater.....but other codes would reveal that in a more explicit way...and this would not act on a cold engine idle...

Drivers are used to control the step motor that sets Idle (Idle AIr Valve) ....I'd be tempted to look in that direction. www.avigex.ca/xport/fuelcontrol_iac.jpg (http://www.avigex.ca/xport/fuelcontrol_iac.jpg) Faulty air idle valve operation could cause high idles as well as stalls ...
ALso notice that vacuum leaks cause high idle.

Code P0123 Throttle Position Sensor Circuit( Signal High Voltage )

Circuit Description
The throttle position sensor provides a voltage signal that changes relative to throttle blade angle.. Signal voltage will vary from .2 to .74 at idle and 5v at WOT.. Throttle Position Signal is one of the most important inputs used by the PCM for fuel control and for most of the PCM control outputs

Trouble Code P0123 will set when
Throttle Position Voltage is greater than 4.8v at any time or
Engine is running and air flow is less than 15 gm/sec
TP sensor signal voltage is greater than 1.1 volts
DTC P0101 Not present
All conditions met for 5 seconds

PCM will default with code P0123 set and not allow cruise control, 4th gear or TCC operating



Code P0401 Exhaust Gas Recirculation Flow Test Failure
The PCM tests the exhaust gas recirculation valve by momentarily commanding the vale ON while monitoring engine RPM.. If the expected drop is not see for a calibrated number of tests, the PCM will set the Check Engine light

The PCM will run the EGR tests when the following conditions are met
Codes P0122,P0123, or P0501 not set
Engine coolant temp is over 185 F
Throttle angle is over 1%
Brake has been applied
Vehicle speed above 25 Mph
Engine speed between 900 and 1100 Rpms


Code P0406, For this Van there is no code 406... The is a Manufacture specific code P1406

Exhaust Gas Recirculation Valve Pintle Position Error

The PCM constantly monitors the EGR valve pintle position sensor to ensure that the valve is responding properly to commands from the PCM

P1406 will set when
EGR pintle position indicates a voltage out of the normal range of the pintle position sensor, or a signal that is 10% greater or less than the PCM's commanded position

Either condition for up to 20 seconds



Code P0640 is actually P1640

This is Quad Driver Circuit #1, There are only 2 things on this circuit, this would be the TCC Solenoid and the EVAP Purge Solenoid..



Code P0670 is actually P1670

This is Quad Drive Circuit #4

The AC Relay
Fan #1( Puller Fan, Radiator side )
Fan #2( Pusher Fan, Condenser side )

Are on the QDM #4 Circuit


I hope this gives you a little bit of a direction to go in..:)

Ok I changed the IAC...probably a waste of money since it didn't really change anything. Idle is high then low...still stalls out a lot. I checked the TPS and it didn't look good...on the scanner while viewing conditions it didn't seem to respond. Checked with VOM as well pretty much no responce and looking across B & C the resistance was way high not 1.5K-4.5K but 80K or better. I changed the TPS and all looks good the power is back, idle is good and so far no stalls. I reset/erased all the codes with the scanner and after about a minute or so the SEL came back on and the same 2 codes came back.

P0640 Quad Driver Module QDM 1 Fault
P0670 Quad Driver Module QDM 4 Fault

The van is running great...these codes must have to do with something else. I didn't mention this before but the AC is not working...I'm pretty sure the clutch assembly/bearings are shot and it is locked up. It spins and sounds nasty but the clutch is not cycling.

Any ideas...

Thanks,
Scott

Car runs great....great!
THe remaining codes have no references in the books for that car.

JRS3800 suggested they were 1640 and 1670 instead:
Code P0640 is actually P1640
This is Quad Driver Circuit #1, There are only 2 things on this circuit, this would be the TCC Solenoid and the EVAP Purge Solenoid..
Code P0670 is actually P1670
This is Quad Drive Circuit #4
The AC Relay
Fan #1( Puller Fan, Radiator side )
Fan #2( Pusher Fan, Condenser side )
Are on the QDM #4 Circuit
and with the info you have just added about the A/C , I think this is plausible.
I'd check refrigerant pressure when spring comes. (not relevant to check that in the cold as pressure would be much below specs anyway).
IN the mean time, I'd bypass the a/c compressor with a shorter belt:
With A/C the serpentine belt is 102.5", PN 1025K6. With out A/C the belt is 72.5", 30" shorter, PN 725K6.
http://www.avigex.ca/xport/serpentinebelt.jpg

thanks for the info on the belt...I'll swap that out and see what happens.

My main concern was to get it running and get my emissions test done and hopefully pass. No such luck, while it seems to be running very good it did fail the emissions test with high NOx...read 5.1517 GPM (state standards 2.6000 GPM) all other test passed. I have until July 2nd to get it tested again or come up with $300 worth of receipts to get a waiver.

The test station told me to look at the following for failed NOx:
A/F mixture may be too lean
Oxygen sensor bad
Faulty EGR
Malfunction of engine spark advance system
Air intake temp too high
cooling system not functioning properly
carbon deposits on intake valves
catalytic converter partially clogged or not functioning properly

Any ideas?

Thanks,
Scott

ABout the A/C, also disconnect the pressure valve near radiator passenger side. THis is just to avoid having another code if pressure is oK and it tries starting the compressor while is has no belt.

FOr the rest:
A/F mixture may be too lean...that would be a consequence of the next.
Oxygen sensor bad..???....or out of scale....possible
Faulty EGR..would definitely have a code for that; dismissed
Malfunction of engine spark advance system....relevant...but improbable, I think..other codes would pop , like knock sensor..
Air intake temp too high...irrelevant in the conditions you operate
cooling system not functioning properly...doubtful..you would have other symptoms
carbon deposits on intake valves....long shot...wow..not going to lift the heads for that...dismissed
catalytic converter partially clogged or not functioning properly...well..this is a possiblity
Not mentioned, failed injector(s)....would push computer control range to limits and would propably pop a code...but a possibility anyway, or compensation might lean or richen ALL the injectors to acheive average O2 contents, but some would be lean, some rich...and Nox does not average....THis is easy reach....personnally, I would check that just to be sure not to have dismissed something easy..
There is an aluminum smelter here pouring 1.3 million tons of CO2 + xxx in the atmosphere every year...and they peek in my exhaust....:screwy:

Scott, just a small question for you..

For the Scan Tool that was used for the van, Will this Tool read the Live Data?

as the Miles on these 3800's add up the O2's get really sluggish and will not trip a code until the O2 is almost DOA.... We have seen a lot of the 94-96 3800's run 60k and have the sensors slow down causing a rich condition of sorts.. Keep in mind you will want to see what the sensor is doing before calling it bad..

In some cases a scan tool can be a great thing to have when working on these 3800's or any car for that matter..:)

Scott, just a small question for you..

For the Scan Tool that was used for the van, Will this Tool read the Live Data?

as the Miles on these 3800's add up the O2's get really sluggish and will not trip a code until the O2 is almost DOA.... We have seen a lot of the 94-96 3800's run 60k and have the sensors slow down causing a rich condition of sorts.. Keep in mind you will want to see what the sensor is doing before calling it bad..

In some cases a scan tool can be a great thing to have when working on these 3800's or any car for that matter..:)

Yes, my scanner reads live data...I was able to look at the TPS and verify it was bad and also that the new one was working properly (also looked at it with VOM as well). Here is a link to the owners manual...I have the Actron CP9145 Super AutoScanner http://www.actron.com/publish/2005/07/22/pdf_english_16150.pdf All the live monitor points are listed in the last couple pages of the manual.

You are right...having a scanner is a great tool and well worth the money. The one I purchased was a great deal and is also good to use on all the cars in my family so that is a plus. I also have an on-board Scanner permanently mounted in my 1989 Pontiac Turbo Trans Am (20th Anniversary/Indy Pace Car). It is a Scanmaster...taps into the diagnostic port and displays pretty much everything. I use it to adjust IAC, TPS and minitor AIT, RPM, ect. and mainly degrees of knock, the main killer of head gaskets and engines on these turbo engines especialy when turning up the boost!!! By the way the engine is the (if you didn't know) Buick 231 (3.8L) Turbo V6...same engine used in the Grand National currently running about 18# boost and soon to be 25-28# but that's another story and big new turbo :wink:

Scott

I have that Tool Too Scott... Its comes in really handy for the 95 and under GM cars... I also have the older CP9110.... But I would like to have the CP9190, I think it is.. It will do Generic and Enhanced OBDII which is good..

Cant tell you how many times the tool has come in handy.. Heck it has even shown me the cylinder that was misfiring on the 94-95 3800's...lol


And Ahhh yes, we love the GN 3.8's as thats where GM learned a lot about the 3.8 and developed the 3800.. I think this is one of the reasons 3800's were such a good engine... Still are

back again...the TPS (aftermarket) I replaced back in Feb has failed...car never passed emissions...have a extension till Oct now. Replaced the AC belt like suggested and unplugged the pressur valve (I think). No more squealing AC compressor clutch bearings...no AC either. Still throwing the Quad Module code ? Getting a replacement TPS from autoparts store...they are going to do it under a warranty. Also what should the O2 be reading on the live data mode in my scanner...I would think a good O2 would be around .750-.850...mine is reading ~.450 ? If that is bad I'm hoping this is the cause of emissions failure?

Thanks,
Scott

back again...the TPS (aftermarket) I replaced back in Feb has failed...car never passed emissions...have a extension till Oct now. Replaced the AC belt like suggested and unplugged the pressur valve (I think). No more squealing AC compressor clutch bearings...no AC either. Still throwing the Quad Module code ? Getting a replacement TPS from autoparts store...they are going to do it under a warranty. Also what should the O2 be reading on the live data mode in my scanner...I would think a good O2 would be around .750-.850...mine is reading ~.450 ? If that is bad I'm hoping this is the cause of emissions failure?

Thanks,
Scott

The Voltage should swing.... You should be in the .100 - .900 area with the swing and see see the O2 cross counts... Something like this... Your van uses the exact same O2 as my Car..

http://img.photobucket.com/albums/v294/Jr3800/th_O2Toggle.jpg (http://smg.photobucket.com/albums/v294/Jr3800/?action=view&current=O2Toggle.flv)

I almost forgot.... If you do buy an O2 sensor... Stay far far away from Bosch...

Either get the Denso, or AC Delco AFS-75

I almost forgot.... If you do buy an O2 sensor... Stay far far away from Bosch...

Either get the Denso, or AC Delco AFS-75

Too late for me ..just changed the front one with ..Bosch..:disappoin

I almost forgot.... If you do buy an O2 sensor... Stay far far away from Bosch...

Either get the Denso, or AC Delco AFS-75

Too late for me ..just changed the front one with ..Bosch..:disappoin

same for me...only have a upstream O2 and it has been replaced with a Bosch as well :uhoh: O2 numbers look good on the scanner.

Installed new TPS and O2...seems to be running pretty good again...still getting the Quad Driver Module codes P0640 & P0670...can't figure out what they are?

i bet it's the iac. have you tested fuel pump or maf?

Installed new TPS and O2...seems to be running pretty good again...still getting the Quad Driver Module codes P0640 & P0670...can't figure out what they are?
fwiw ..don't have a PO670 code showing in Haynes & a quick google of 'gm (or pontiac) code PO670' brings up Glow Plug Module Control Circuit..

Haynes also shows PO650 (no PO640) for Quad Driver Module Circuit.

I didn't realize 94 was OBD II compliant as well, as 95 models. The following applies to 95 model but I suspect may very well apply to your 94. Code 1640 is QDM #1 fault, and the manual states the following symptoms:
TCC inoperative
rough or high idel due to evap purge solenoid being "on" all the time.
This driver permits the PCM to allow higher current devices ( solenoids ) to be controlled by the pcm. Power is supplied to the circuits from the hot key side, and is grounded through the pcm. Check for shorts on the dark green/white wire from the evap solenoid ( located on a bracket located on the rear on the engine just beind the fuel injectors) or the tan/black wire on the TTC apply solenoid loacted inside the transaxle. If it were to be shorted to ground the tcc will be contastantly trying to engage, and will result in sluggish performance.
Code P1670 is QDM # 4 fault, and controls A/C relay, and pusher and puller fan relays. You say you have AC problems, again check the dark green/white wire off the ac relay for shorts or opens.
The evap canister solenoid problem is emission related and could be the reason for your failure in testing. Check for 12V at the solenoid, it should be cycling but I suspect it is staying on, allowing lots of air into the engine, hence the high idle. However, tha manual also goes on that is there is no short to ground in the circuit, replace the pcm.
Good luck
Jeff

The 94-95 3800 Powered U Bodies are not OBD2 compliant... They are full on OBD1 but they use OBD2 codes... These PCM's were the step before GM went to OBD2 in 1996.. So its sort of a mixed computer..

But with the code presented, do as the poster above has stated... The PCM is seeing an issue with one of the items on that circuit:)