93 Corvette Smog pump trouble shooting
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
I know someone knows how to diagnose my 93 Corvette air pump ,smog pump mine will not come on .. I put power to the pump it works but I don't know what tells it to come on .. Thanks ..
Le Mans Master
Joined: Sep 2013
Posts: 6,192
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From: near the thumb in the mitten
AIR is diagnosed Chart C-6 of FSM if you have or can get access to manual. AIR system is partially diagnosed with a Tech1 unfortunately. There are 3 fuses involved a 20a maxi fuse to pin E of relay. 10a ENG2 to pin D of relay that powers relay coil. A 25a fuse between pin A of relay and AIR pump. ECM grounds pin F to turns on AIR pump. Pin C of relay is not used. I would do voltage checks at relay, see if pump is getting voltage, and if relay is turning on. Grounding pin F should turn on pump.
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
AIR is diagnosed Chart C-6 of FSM if you have or can get access to manual. AIR system is partially diagnosed with a Tech1 unfortunately. There are 3 fuses involved a 20a maxi fuse to pin E of relay. 10a ENG2 to pin D of relay that powers relay coil. A 25a fuse between pin A of relay and AIR pump. ECM grounds pin F to turns on AIR pump. Pin C of relay is not used. I would do voltage checks at relay, see if pump is getting voltage, and if relay is turning on. Grounding pin F should turn on pump.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Pump does not have 12v with key on. ECM grounds relay to send 12v to AIR pump 25a fuse which is between relay and pump. Maxi fuses have battery voltage. ENG2 has ignition voltage.
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
Thanks for the info , do you know if the pump has power going to it all the time .. What has to happen for the pump to come on ?? and no I don't have a manual but if keep finding problems with this 93 may be finding one had one years back I think I sold it ,what was thinking I know was not going to buying any more C-4s wrong answer .. Thanks ..
Team Owner
Joined: Sep 2003
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Last edited by WVZR-1; Nov 6, 2018 at 01:25 PM.
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Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
Thanks , the fuse must be in the wiring harness witch sounds kinda weird ( even for GM ) The Black & Orange wire comes right out of the AIR motor plug and goes right in to the harness and right to the outside fuse box were fuse 20a is ( AIR fuse ) ,there nothing you can see that might be a fuse it has to be in the harness ??? I read somewhere can't remenber but I think in in the plug itself ??? Myself and 93 going to be in the Vet . parade this Sat. in Houston TX so will open it all up next week . The fuse got to be in the harness . The motor not getting power . I need to check that one 25a fuse and go from there . Thanks ..
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
I looked at it again and there is nothing that you can see after the plug ,the wire just goes in to the harness and is kinda lost behind the Batt. but looks like it goes through the fire wall . It might behind the or under the radio with some more relays ECT. I think are back there .. I have to take out the BAtt. and see what the heck is going on with the fuse .. IF the wire is going into to the firewall got to be in the dash ???
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
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From: Birmingham Al
Found it and yep blown ,can't see it standing over the pump its over kinda on the the bottom side and is not after the relay plug or the black/orange wire ??? I was flowing the wire and its like no fuse here . Saved me lots of work .. I have a manual coming and will not ever say no more C-4s . Been trying to get the Check/ENG. light to go off this may be the reason .. EVAP #26 keeps coming up been replacing most of the EVAP stuff ,canister went bad and charcoal all in the lines ( big mess) .. Thanks , its people like you that keep the Corvette hobby alive and myself as well pass all I know to anybody that's will lesion .. Have a great day .. Mike 68 non war vet for my buds that did not make it back might not been a war might have been HELL.
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
I apologies if I got a little off track being a Vietnam Vet. around this time of year I start thinking about all my HOT RODS buds in high school and the fact I am enjoying the Corvette life style and they are not here with me and I don't know why .. Thanks again for your help .. and no the pump still will not turning on going to take it off and bench test it might just might be a bad pump .. Its 25 years old .. NO big deal I have replaced everything else what's one more part ..
Thread Starter
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
Update : A little late busy working on other peoples s C-4s anyway ,blown Smog pump fuse charcoal in all the lines bad Canister and bad purge valve and last but not lest the EVAP bypass valve plug not locked in all the way ( very hard to see) Replaced parts blew- out re-pluged and just went over everything ,light off system working ,morel of the story just keep digging and getting some help goes a long way . .. Thanks
1st Gear
Joined: May 2020
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Reviving an old thread I know, but this helped me more than you will know. I just purchased my first C4, a 93 auto. The previous owner did what he could for the car but I think he got frustrated trying to track down this issue. I got the car for a good price because of the service engine light being on. I've already replaced the EVAP solenoid valve which did not fix the issue and I didn't want to just start replacing everything else and hoping for the best. Long story I'm sorry, but after reading this forum, I went out and checked mine. Sure enough, the fuse was blown. Now to wait for the morning to start her up and go for a test drive. Fingers crossed the light stays off this time.
