1995 Chevy Truck TBI and /or DIS issues

Tiny
KALANIKAAU
  • 1995 CHEVROLET TRUCK

Engine Performance problem
1995 Chevy Truck V8 Two Wheel Drive Manual 150K miles

Bone stock code H (305) engine mated to a 5 spd. Manual trans.
About 6 months ago, during a severe thunderstorm here, the truck suddenly and un-expectedly starting running badly, no power off of idle, increasing throttle opening further would cause it to stall.
This truck is used infrequently so I just ignored the problem.
Now the problem has progressed to the point where I need to manually prime the TBI bores with carb. Cleaner just to start it Once it does run, I need to feather the throttle just to keep it running. Also, a huge amount of air bypasses the IAC, creating a massive vacumn leak.
So far I have checked fuel pump pressure (12 psi)
Read codes from ECM, besides the normal code 12 a code 33 was displayed. This points to the MAP sensor, which I have replaced, I even cleaned out the vacumn source for this sensor, it's attaching hose is intact.
I do not usually replace engine management sensors at will, but the IAC, coolant, MAP and TP sensors are new also, I am desperate.
Evidently there is an issue now with the injectors not firing during startup, can anyone give insight as how to diagnose this? Perhaps no signal from distributor?
Also. What would cause the IAC to allow a huge amount of air bypassed?
Getting back to the TP, I believe I have installed it properly, just to verify resistance varies from.5 volt to 4.5 at WOT, what should resistance readings be for idle to WOT?
Hope someone can help !

Do you
have the same problem?
Yes
No
Friday, June 5th, 2009 AT 5:43 AM

16 Replies

Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

Hi
Think you may need an Ignition control module located in distributor. Must signal PCM engine is cranking to fire injectors on start up.
Hope this helps
Thanks for donate

Was this
answer
helpful?
Yes
No
Friday, June 5th, 2009 AT 1:33 PM
Tiny
KALANIKAAU
  • MEMBER

Thanks for the advice on the ign. Module, I can surely see how that would affect injector operation.
Can you offer insight as to why the IAC is allowing such a huge amount of air to bypass too?

Was this
answer
helpful?
Yes
No
Saturday, June 6th, 2009 AT 12:37 AM
Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

Maybe carbon deposits. Remove and clean pentil, passage ways. Then plug in turn key on observe pentil does it move? If no then newIAC

Was this
answer
helpful?
Yes
No
Sunday, June 7th, 2009 AT 3:08 PM
Tiny
KALANIKAAU
  • MEMBER

I've already removed an replaced the IAC motor, while I had it out I also cleaned the needle seating area, some how the ECM is telling the motor to open fully (counts)? Or pretty much close to full open because it creates a massive vacumn leak. While I do understand the entire concept of bypassing air around the throttle plates to increase the idle, this leak is simply huge
This is with the engine cold, as it warms up the valve closes somewhat and the engine will actually idle then.
The coolant temperature sensor is new also.

Was this
answer
helpful?
Yes
No
Sunday, June 7th, 2009 AT 6:34 PM
Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

Check out the IAT intake air temp sensor. Located top right center of intake manifold. Check resistence across terminals should be 3400 ohms at 70 deg. Resistence drops as air temp goes up.
Do you get injector spray at start up?

Was this
answer
helpful?
Yes
No
Wednesday, June 10th, 2009 AT 9:01 AM
Tiny
KALANIKAAU
  • MEMBER

Will try to locate the sensor (IAT) you describe, do you have a picture of it?
No, the injectors do not spray at startup, would this be caused by this sensor?
I was thinking that the DIS module may be at fault for the no spray problem, do you concur?
Thanks for your time and effort !

Was this
answer
helpful?
Yes
No
Wednesday, June 10th, 2009 AT 12:46 PM
Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

Did you have the ignition control module checked?
Not sure what you mean by DIS the PCM grounds injectors when it receives dist. Rotation from ICM

Was this
answer
helpful?
Yes
No
Wednesday, June 10th, 2009 AT 1:45 PM
Tiny
KALANIKAAU
  • MEMBER

By DIS I am referring to the distributor assy. Itself.
Are you certain of a IAT (Intake Air Temperature) sensor on this engine?
There is a coolant temperature sensor screwed into the intake manifold (water jacket) adjacent to the t/stat hsg.

Was this
answer
helpful?
Yes
No
Wednesday, June 10th, 2009 AT 4:00 PM
Tiny
KALANIKAAU
  • MEMBER

By DIS I am referring to the distributor assy. Itself.
Are you certain of a IAT (Intake Air Temperature) sensor on this engine?
There is a coolant temperature sensor screwed into the intake manifold (water jacket) adjacent to the t/stat hsg.[/Quote:ad2bc5e5f9]

Well, it's been a week since my last question, with no response at all.
Guess you've given up on my problem, I have'nt
Thanks anyway for the tips

Was this
answer
helpful?
Yes
No
Wednesday, June 17th, 2009 AT 6:56 PM
Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

Did you have the module checked inside distributor?

Was this
answer
helpful?
Yes
No
Thursday, June 18th, 2009 AT 9:49 AM
Tiny
KALANIKAAU
  • MEMBER

The module has been replaced with a new unit, the problem still persists

Was this
answer
helpful?
Yes
No
Thursday, June 18th, 2009 AT 10:14 AM
Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

O.K. Test light on injector harness check for battery voltage to harness both should have power key on.
Let me knoe results

Was this
answer
helpful?
Yes
No
Thursday, June 18th, 2009 AT 10:39 AM
Tiny
KALANIKAAU
  • MEMBER

By DIS I am referring to the distributor assy. Itself.
Are you certain of a IAT (Intake Air Temperature) sensor on this engine?
There is a coolant temperature sensor screwed into the intake manifold (water jacket) adjacent to the t/stat hsg.[/Quote:e674e1c946]

Well, it's been a week since my last question, with no response at all.
Guess you've given up on my problem, I have'nt
Thanks anyway for the tips[/quote:e674e1c946]

Problem solved, it was the fuel pump after all, at times it would supply 12 psi, yesterday it could barely muster 2 pounds.
Good lesson learned here, in tank pumps don't always fail completely, this one was just plain tired
Thanks for the help !

Was this
answer
helpful?
Yes
No
Sunday, July 12th, 2009 AT 4:10 PM
Tiny
DOCFIXIT
  • EXPERT
  • 19,035 POSTS

Glad you found problem lucky you rechecked pressure and pump was acting up. Hope it's smooth trucking from here on out.

Was this
answer
helpful?
Yes
No
Please consider a donation if we helped you
Monday, July 13th, 2009 AT 1:14 PM
Tiny
COLEGAGE2001
  • MEMBER

I changed everything he did and my tbi still want spray.
But it runs great for a while then when I kill it have to wait bout 24 hrs to crank back up

Was this
answer
helpful?
Yes
No
Thursday, January 26th, 2012 AT 9:55 PM
Tiny
RIVERMIKERAT
  • MEMBER

Colegage, have you check your fuel injection fuse and relay?

Was this
answer
helpful?
Yes
No
Saturday, January 28th, 2012 AT 9:44 AM

Please login or register to post a reply.

Related OBD1 Code 12 Questions

Recommended articles