TABBOO

Well I got my car out of storage looking forward to the cruising season and when I start it cold it throws codes 34 41 and 42. If I drive it awhile the check engine light goes out and everything is fine. If anyone can give me any ideas on how to proceed it would be greatly appreciated.

Bob88GTA

iTrader: (2)

YOU CAN START HERE

CODE 34
Trouble Code 34 indicates that the Manifold Absolute Pressure (MAP) sensor is detecting unusually high vacuum in the manifold. Code 34 will get set when:
? Engine RPM less than 700.
? Manifold pressure reading less than 13 kPa.
? Conditions met for .22 second.

OR

? Engine RPM greater than 700.
? Throttle angle over 20%.
? Manifold pressure less than 13 kPa.
? Conditions met for .22 second.

Possible causes include:
1. Faulty MAP-to-ECM connection
2. Defective MAP sensor
3. Defective ECM
Check the shop manual for details on vehicle specific MAP sensor applications

CODE 41
Trouble Code 41 indicates an incorrect MEM-CAL has been installed or it is faulty and it must be replaced.
Possible causes include:
1. Faulty connection due to MEM-CAL not locked in place.
2. Incorrect MEM-CAL installed.
3. Faulty MEM-CAL.

CODE 42
Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system. During cranking, the timing is controlled by the ignition module and the ECM grounds the EST line. It expects to see no activity on this line at this time. When the ECM enters EST mode, it applies +5 volts to the BYPASS line and expects to see voltage variations on the EST line.
Reasons for the ECM to set Code 42:
? System in BYPASS mode (i.e. EST line supposedly grounded) but activity sensed on EST line
? System in EST mode (i.e. BYPASS line driven with +5 volts) but no activity seen on the EST line

Possible causes include:
1. BYPASS line is open or grounded
2. EST line is open or grounded
3. Poor connections between ignition module and ECM
4. Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise
5. Faulty or incorrect ignition module
6. Faulty ECM

TABBOO

Should I just replace the prom with the original Gm one since I have a Hypertech that I bought on ebay several years ago installed now? Does the code 34 refer to MAF instead of MAP since my car is a 1987? Thanks for the quick reply!!

RBob

iTrader: (1)

Code 41 is a cylinder select error. This is part of the CALPAK resistors on the stock MEMCAL, which needs to be plugged into the Hypertech adapter.

Yes, it refers to the MAF sensor, 34 being that the MAF is reporting too low of an airflow for the engine RPM & TPS% value. Might be a leak in the ducting between the MAF and intake. Or an intake manifold leak, which would likely cause a high idle.

RBob.

TABBOO

I cleared all of the codes today and I checked the timing wire on the firewall and sure enough the plug wasn't tight. I started the car and it still threw a code 41. I then pulled the ECM and switched out the Hypertech prom with the original prom and all problems solved.
Now for the strange parts the Hypertech prom has been in the car for about 5 years, it was purchased used from Ebay and when I looked at the box it came in today (original GM prom was stored in box) it stated the chip was for an 87 305 TPI auto but I noticed it said 50 state legal. I then peeled off some tape used to seal the box and the part number was for a California chip. I will run with the GM PROM until I can get the right Hypertech or see if I can pay someone to burn me a better chip.
The other strange thing is I haven't messed with the timing wire plug for about 6 years since the last time I set the timing.
I would like to thank you guys for the prompt help pointing me in the right direction, problem solved quickly due to the great support from Thirdgen.org members as always.