Missing When hot
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Joined: Apr 2005
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Car: 86 Z28 camaro t/tops
Engine: 305TPI stock
Transmission: turbo 700
Missing When hot
I have a 86 tpi which runs well until i have been driving for about 30min than it starts to miss the more i drive the worst it gets .Code 33 comes up my tpi as a maf sensor which i think is playing when it gets hot.I was wondering if i was on the right track
Brett
Brett
Joined: Jul 2003
Posts: 10,521
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From: NYC / Jersey
Car: 1990 Trans Am GTA
Engine: Turbo 305 w/MS2
Transmission: 700R4
Re: Missing When hot
Originally posted by ausZ28.I have a 86 tpi which runs well until i have been driving for about 30min than it starts to miss the more i drive the worst it gets .Code 33 comes up my tpi as a maf sensor which i think is playing when it gets hot.I was wondering if i was on the right track.
Run a search with the name "Vader", as he has written thousands of posts relating to both the causes and effects of Code 33....
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If you buy a new MAF, send your old one to me. I could use a good spare.
A DTC 33 means the MAF sensor indicated an air flow of 45 gm/sec or more for 1 second when TPS was less than 25% and the engine RPM was below 2,000.
It is frequently caused by a TPS voltage that is too low, or is reporting low voltage due to poor connections. If the MAF is reporting too much intake air flow, that means it is reporting air flow. That's all a MAF is supposed to do. It is probably working just fine.
Another possible cause is that the ECM is not getting all reference pulses from the HEI module in the distributor, but that would normally be accompanied by misfire or lean backfire due to missed injector firings.
The third possibility on your '86 is addressed in the TSB (Technical Service Bulletin) issued by GM regarding all 1986 TPIs for a faulty PROM. I had the same thing on my '86, and got the replacement "calibrator" from GM for about $60. I had previously tried a HyperTech CALPAK in my '86 and it solved some of the issues, but the factory replacement was even better. My custom programming is far better yet.
That low TPS could also explain some of your other driveability issues, creating a lean tendency whenever you drive. These same issues are addressed in that TSB:
A DTC 33 means the MAF sensor indicated an air flow of 45 gm/sec or more for 1 second when TPS was less than 25% and the engine RPM was below 2,000.
It is frequently caused by a TPS voltage that is too low, or is reporting low voltage due to poor connections. If the MAF is reporting too much intake air flow, that means it is reporting air flow. That's all a MAF is supposed to do. It is probably working just fine.
Another possible cause is that the ECM is not getting all reference pulses from the HEI module in the distributor, but that would normally be accompanied by misfire or lean backfire due to missed injector firings.
The third possibility on your '86 is addressed in the TSB (Technical Service Bulletin) issued by GM regarding all 1986 TPIs for a faulty PROM. I had the same thing on my '86, and got the replacement "calibrator" from GM for about $60. I had previously tried a HyperTech CALPAK in my '86 and it solved some of the issues, but the factory replacement was even better. My custom programming is far better yet.
That low TPS could also explain some of your other driveability issues, creating a lean tendency whenever you drive. These same issues are addressed in that TSB:
Code:
PONTIAC ROUGH IDLE, CHUGGLE, LOW SPEED. Page: 1
86-6(GAS)-66 Issued: 10/17/86
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1986 FIREBIRD VEHICLES WITH 5.0L LB9
TPI ENGINE (ENGINE CODE F)
New service calibrators (Ref: Called Mem-Cal In Shop Manual) have been
released for the 1986 Firebirds with the 5.OL TPI engine. These new
calibrators will address the following customer comments:
1. "Rough Idle" on both hot and cold engine - the idle speed is raised to 650
plus or minus 50 RPM.
2. "Chuggle or Shudder" at low speeds - torque converter clutch (TCC)
engagement speed is raised to 41 MPH.
3. "Hesitation" on light acceleration with a hot engine.
4. "Cold Driveability" - New calibration eliminates light to moderate sag on
cold driveaway.
5. "Service Engine Soon” Lights - Eliminates the following false Codes:
A. Code 32 - EGR System failure
B. Code 33 - Mass Airflow Sensor Voltage High
C. Code 34 - Mass Airflow Sensor Voltage Low
D. Code 43 - Electronic Spark Control
E. Code 44 - Lean Exhaust Indication
If normal engine diagnostics and repair do not correct the above conditions,
it will be necessary to replace the calibrator in the ECM. Below is a listing
of the new calibrators and their usages.
ON AIR CONDITIONING (C-6O) FIREBIRDS
With QYZ (P215/65 R 15/N 15" Tire) Use - 1228290 Calibrator
With QAC (P235/60 VR 15N Tire) Use - 1228291 Calibrator
With QDZ (P245/50 VR 16N Tire) Use - 1228291 Calibrator
ON NON-AIR CONDITIONING (C-41) FIREBIRDS
With QYZ (P215/65 R 15/N 15" Tire) Use - 1228292 Calibrator
With QAC (P235/60 VR 15N Tire) Use - 1228293 Calibrator
With QDZ (P245/50 VR 16N Tire) Use - 1228293 Calibrator
Use Applicable Labor Time and Operation Numbers.
1228291 Calibrator available $63.64 F.O.B. factory Thread Starter
Junior Member
Joined: Apr 2005
Posts: 3
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Car: 86 Z28 camaro t/tops
Engine: 305TPI stock
Transmission: turbo 700
Well I have been driving a bit more same problem but no trouble codes car goes well for about 20 min than hesitate and coughs.Change harmonic damper,I have thought it could be a bad ECM earth going to strip harness back to check more thoughly. strange thing the car runs perfect in reverse. that why i am checking earths as the engine loads up different in reverse.Will be checking fuel pressure in morning as the pump does not appear to be making the same about of noise when the ignition is on.The factory tacho does some funny things when the car misses like it flicker up and down are lot.Just a thought it couldnt be the park/ neural switch
Brett
Brett
Last edited by ausZ28; Nov 24, 2005 at 06:10 AM.
Junior Member
Joined: Apr 2006
Posts: 2
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From: Harrisburg IL
Car: 1988 Pontiac Firebird
Engine: 305 TPI bored 30
Transmission: T5
Axle/Gears: 3.42 Limited slip
Not sure of that. I have an 88 tpi that is doing the same thing miss at high temp. I have replaced the cap rotor plugs and wires alternator and battery. still does it. ANY IDEAS.
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