mstwtd007

so ive got my 93 z28 lt1 had a code 26. ses light come on during ignition, car would hesitate. rplaced air pump, egr solinod, evap solinod. getting a little better. now the ses light only comes on when my car reaches 200 degress or so. never got over 140 before i replaced everything. i wanna get my egr valve off and cleaned. is there also a problem with my t-stat. im just stuck and stumped at this point

Zfbod94

Courtesy of Injuneer: 26 - Evaporative emissions canister purge solenoid circuit.

I see that you replaced the Evap solenoid already. Did you check the wiring for the circuit. Im not sure what voltages you need to look for, but you can at least check for continuity in the circuit. Im sure someone else can chime in on what voltages you need to look for.

Injuneer

No. That's the code description for 94/95. The 93's are different. The ECM incoporates several "quad driver modules".... used to operate high amp circuits like the solenoids. DTC 26 in a 93 is (courtesy of Shoebox):

Quad-Driver Module (QDM) #1 circuit
applies to:
- AIR pump relay circuit
- EGR solenoid
- EVAP solenoid

In all cases these are based on electrical circuit continuity. In the case of the AIR pump, all it is checking is the fuse in the AIR pump circuit. You can just unplug the AIR pump, put a good fuse in the circuit, and not get a code for the system. Check the fuse.

For EGR, it is only checking the EGR solenoid circuit, as described above. EGR system could be totally removed, except for the solenoid, and you don't get DTC 26 (you could get DTC 32 for EGR system performance). No need to clean or replace the EGR valve unless you also have DTC 32.. It's for the solenoid electrical circuit. Could be the wiring or conector since you replaced the solenoid.

Key on, check for 12V on the brown wire to each solenoid harness connector. The ECM provides the ground to open the solenoid.

I beleive DTC 26 would also set if the QDM #1 in the ECM is defective, but not sure. I looked it up in my 93 shop manual and it does indicate cause could be "faulty ECM".

Shoebox's code list - note that the 93 codes, where different from 94/95 are shown on the right side of the chart.

http://shbox.com/1/Dtcs.htm

mstwtd007

hey thanks i checked the voltages and got 12 on both solinods. the air pump fuse is good as well as the relays. there is a new computer in the car i installed a month ago. its the darnest thing that before i replaced everything the car never went above 140 and now gets to 200 and then ses light comes on and then temp goes back to 140 everytime. it stays at 140 after all that mentioned before untill i turn the car off. i can restart it minutes later then the same events happen. am i know just outta pure luck the t stat is going out but as far as i can recall that wont turn on the ses light or is there some kind of other temp sensor in the mix somewhere. i havent got a chance to check the voltage on the air pump due to rain and puddles on the ground. when i do check it what voltage should i look for?

Injuneer

The AIR pump itself will not set a code. You could remove it from the car, and as long as the fuse and the relay are OK, you won't get DTC 26. The pump runs for a couple minutes on startup to help the cats heat up, and then doesn't run again until the next start.

140* is probably not the engine coolant temp. The 93 gauges are marked differently than the 94-97 gauges, with the first line marked 100*F. The 94-97 gauge is marked 160*F. 140*F would not be good for the engine, and it's marginal as far as the ECM kicking A/F ratio control into closed loop. There is no reason a 93 would run 40-50*F cooler than the later years. I think the gauge is simply mismarked.

http://shbox.com/1/temp_gauges1.jpg

Running at 200*F is not unusual. GM designed the engine to run at 210*F. There would be no reason for any light (SES, or check gauges) to come on at 200*F. There is no way the ECM could tell the t'stat isn't working. The coolant temp sensor has it's own codes. The fan relays also have their own codes.

Many codes cause the fans to run continuously, which would explain why the coolant temp drops back to what you believe is 140*F, when the SES light comes on. The fans running constantly, in response to a trouble code could cause that. The control system is probably running correctly, without the fans when the engine runs at 200*F.

Are you sure DTC 26 is the only code?

mstwtd007

as far as me saying 140 because if i divide the hash marks between the numbers 100 and 260 then the second i would quess to be 140 if every hash being equal value. i gonna dive it one day this week and runn a computer on it at my friends place and get back to ya. thanks

Zfbod94

Sorry for the misinformation OP. I was under the impression that OBD1 is OBD1 accross the board. I hate giving out incorrect info. Thank you for the correction Injuneer. I learn something new everyday