94 Trans Sport 3.8 no power, stalls...

[scottd60]

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

[LMP]

Originally Posted by scottd60

.. 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.
; I think early '94 still had that configuration then changed and then it needs a scanner.

[scottd60]

Originally Posted by LMP

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.
; 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

[Jrs3800]

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 ....

[scottd60]

Originally Posted by Jrs3800

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.

[LMP]

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.

[scottd60]

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

thanks

[Jrs3800]

Originally Posted by scottd60

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?

[scottd60]

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...

[Jrs3800]

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

[scottd60]

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

[Jrs3800]

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


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..

[scottd60]

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

[Jrs3800]

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..

[LMP]

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.