alot of problems, but no answers.
02-12-2009, 05:27 PM
#1
Registered User
Thread Starter
Join Date: Oct 2008
Posts: 34
alot of problems, but no answers.
have an 87 iroc-z with a 5.7L 350. its bored .04 over and has a few internal upgrades. it recently failed emissions and has had a history of surging idle since i bought it in august of 08. it also has a hyper tech chip
what ive replaced:
temp sensor (for guage)
MAF
Plugs
Wires
Coil
O2
EGR
160* T-stat
oil pressure sensor (for guage)
i just did the timing today and its dead on. i noticed the engine runs alot better without the EST plugged in, no surging no dieing. when i plug the EST back in it will surge like crazy and die. it also almost dies when you put it into gear. there's no response from the ecm when i try to scan for codes with the EST unplugged, no DTC's but the ses light is on. plug the EST back in and the SES light goes off.
im really at a loss at this point because it surges like crazy and dies, but theres no SES light. when i started it today it was shaking like crazy like it had a big cam, but went away as it warmed up.
any help will be GREATLY appreciated, and i would like to fix as much as possible before the 20th when i have to go back for emissions. thanks to all.
what ive replaced:
temp sensor (for guage)
MAF
Plugs
Wires
Coil
O2
EGR
160* T-stat
oil pressure sensor (for guage)
i just did the timing today and its dead on. i noticed the engine runs alot better without the EST plugged in, no surging no dieing. when i plug the EST back in it will surge like crazy and die. it also almost dies when you put it into gear. there's no response from the ecm when i try to scan for codes with the EST unplugged, no DTC's but the ses light is on. plug the EST back in and the SES light goes off.
im really at a loss at this point because it surges like crazy and dies, but theres no SES light. when i started it today it was shaking like crazy like it had a big cam, but went away as it warmed up.
any help will be GREATLY appreciated, and i would like to fix as much as possible before the 20th when i have to go back for emissions. thanks to all.
02-13-2009, 01:56 PM
#4
Registered User
Thread Starter
Join Date: Oct 2008
Posts: 34
from what i can see, there arent any vaccum leaks. havnt replaced the iac due to cost. any way to bench test it?
i think the only internal upgrades is that it's bored .04 over and has a slightly larger cam if im not mistaken. i didnt do the work to the car, i bought it that way and they did a horrible job with it.
i think the only internal upgrades is that it's bored .04 over and has a slightly larger cam if im not mistaken. i didnt do the work to the car, i bought it that way and they did a horrible job with it.
02-13-2009, 03:15 PM
#5
Registered User
Join Date: Dec 1998
Location: Haslett, Michigan
Posts: 2,161
IAC isn't too expensive, expecially if you pick up a used one. However you can remove it, and scrub the carbon off the IAC pintile and the inside passages. That'll usually clean up the IAC malfunction, if there is any.
Another thing to try is to unplug the ECM and re-plug it. You do the same with the PROM.
Then there is the EST module on the firewall, plus the knock sensor. You should be able to unplug the knock sensor itself to see if EST is tossing a bunch of false timing retard into the system.
Also, when you timed the engine, did you first unplug the ECM from the distributor before setting inititial timing? 8 degrees BTDC is base timing with no ECM advance. When you plug the ECM in, timing should advance another 10 to 20 degrees at idle.
At last resort, buy some used sensors and start swapping them out. MAP, EST module, knock sensor, #165 ECM, they are all pretty cheap these days, especially if you pick them up from one person on thirdgen.org. There's lots of guys on there with that kind of stuff in their junk drawer.
Another thing to try is to unplug the ECM and re-plug it. You do the same with the PROM.
Then there is the EST module on the firewall, plus the knock sensor. You should be able to unplug the knock sensor itself to see if EST is tossing a bunch of false timing retard into the system.
Also, when you timed the engine, did you first unplug the ECM from the distributor before setting inititial timing? 8 degrees BTDC is base timing with no ECM advance. When you plug the ECM in, timing should advance another 10 to 20 degrees at idle.
At last resort, buy some used sensors and start swapping them out. MAP, EST module, knock sensor, #165 ECM, they are all pretty cheap these days, especially if you pick them up from one person on thirdgen.org. There's lots of guys on there with that kind of stuff in their junk drawer.
02-13-2009, 05:40 PM
#6
Registered User
Thread Starter
Join Date: Oct 2008
Posts: 34
i unplugged the balck/tan wire like it says in my manual to set the base timing. under the hood it said about 6 degrees, but its withing 2 degrees.
i did unplug the prom and re-seat it. ill do the ecm tomorrow. and ill unplug the knock sensor from the block and see if there's any change.
oh yeah i forgot to mention that the fan is constantly running on high, no matter the temperature. so i had to unplug the secondary fan relay.
i just put that iac in in before winter, i changed the tb and swapped out the sensors so they are still the same ones.
i did unplug the prom and re-seat it. ill do the ecm tomorrow. and ill unplug the knock sensor from the block and see if there's any change.
oh yeah i forgot to mention that the fan is constantly running on high, no matter the temperature. so i had to unplug the secondary fan relay.
i just put that iac in in before winter, i changed the tb and swapped out the sensors so they are still the same ones.
02-13-2009, 08:14 PM
#7
Registered User
Join Date: Dec 1998
Location: Haslett, Michigan
Posts: 2,161
Fan on, all the time eh? IIRC, one fan is controlled by the ECM whereas the other is controlled by a thermal switch. Can you determine which one is turning on? If it's the ECM controlled fan, perhaps what you have is a failed ECM!
02-15-2009, 09:19 AM
#9
Registered User
Join Date: Sep 2008
Location: NY
Posts: 88
02-18-2009, 12:27 PM
#12
Registered User
Thread Starter
Join Date: Oct 2008
Posts: 34
well im still waiting on my new ECM, but i have another question that i thought i might as well ask.
theres a 2 pin male plug from my wiring harness hanging down next to my oil filter and i have no clue what it belongs to. nothing looks to be unplugged.
and is there supposed to be a second O2 sensor after the cat on my exhaust?
theres a 2 pin male plug from my wiring harness hanging down next to my oil filter and i have no clue what it belongs to. nothing looks to be unplugged.
and is there supposed to be a second O2 sensor after the cat on my exhaust?
02-21-2009, 02:53 PM
#14
Registered User
Thread Starter
Join Date: Oct 2008
Posts: 34
well i realized that i may have a vacuum leak after all. i just always thought i needed a brake job when i could put the brake pedal on the floor.... but it started building up pressure yesterday. i guess ill have to sort through the vacuum system.... any one know where i can find a diagram?
