vetteoz
Well-known member
Maybe you do have a ECM problem
When jumpered ECM should be in diagnostic mode and display any fault codes present
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Corvette C4 1984 - 1996 Electronic Control Module Recovering the Codes
Question: cooling fan question here.
- Thread starter vernh
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When jumpered ECM should be in diagnostic mode and display any fault codes present
Read
Corvette C4 1984 - 1996 Electronic Control Module Recovering the Codes
boomdriver
Well-known member
I'd start by tracing the fan relay wires...the blue(?) is the one that you want to see .. (going from memory here)
It sounds as if someone attempted to splice in their own switch system or bypass and may have left the signal wire incomplete or cut somewhere.
It sounds as if someone attempted to splice in their own switch system or bypass and may have left the signal wire incomplete or cut somewhere.
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- #23
vernh
Member
vetteoz you seem extremely knowledgeable about the cars hats off to you. I am wondering if you might know where the ecm is grounded. I followed directions on recovering codes and I got no flashes no nothing. I am curious if it isn't grounded if I wouldn't recieve any errors. This car has sat for many years. I have repaired several things but currently two issues are cooling fans operating and high idle. It idles around 1700 rpm and backfires slightly when gas is applied. I was just curious if maybe the ecm isn't grounded. First time it got a little hot i pulled radiator cap to check if it was full. some oosed out and it does show a low coolant message from time to time. Which might indicate ecm is grounded. Not quite sure on that. Could it be that only certain parts of the ecm are bad. Would i be to the good to get a scan tool and see if it will communicate with ecm? sorry I keep bothering you with this but you seem very knowledgable.
John Robinson
Gone but not forgotten
The ECM ground should be a braided cable that is grounded to the bell housing with about 3 or 4 other wires just above the oil filter. Also there should be two grounds behind the battery that are a little tough to get to. For them you will have to remove the battery.
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- #25
vernh
Member
Thank you the three by the oil filter I have pulled and cleaned. I didn't check for continuity back to ECM plug but will. Also will check ones behind battery. Thank you.
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- #26
vernh
Member
Gonna throw one more crazy idea at you guys and then I will leave you alone. I promise. Quick story the guy I bought this car from had lost the key. My step father is a part time locksmith. He said he could make me a key. I was amazed that he did and it started the car. Is it possible that the key will start the thing but not be just right and allow the ecm to make adjustments and all to engine idle and fans coming on etc. ? I guess what I am saying is key good enough to start the car but not just right for other things.
boomdriver
Well-known member
Nope..not possible.
He had to have somehow got the correct key resistor code in order to make a key that works. The VATS is anti-theft...not alarm or ECM tune related. It simply interrupts power to the starter and fuel injection if triggered. You cannot just "fit" a new key without being able to read the resistor code for the key that WAS in the car..Keys and ignition switches are matched. Knowing there are around 15 possible key codes, and that whenever ANY wrong key is turned in the ign switch that shuts down the system for up to 12 or 15 minutes....its possible to try making a key and take all day long if you do not know the code for that ign switch. If he just got lucky and hit it the first time....I'd send him to the store to buy lottery tickets.......Thats how the system defeats a thief...thieves do not have the time to try this or that and wait for the system to release the starter and fuel inj...they move on to a ford or some other easy target.
If a key was "fitted" then they got extremely lucky getting the correct VATS code OR the VATS itself has been bubba'd and bypassed. THAT might be something to look at, a cheap VATS bypass module thats causing run issues.
Your ECM will not work period, won;t even crank over if its (ECM) not grounded or connected. They don't sorta work or kinda work...its all or nothing. The car would be like a headless chicken....quite dead.
Not sorta or kinda...but dead.
The ECM ground is not the braid but one of the black wires on the bolt on the block near the oil filter. A stack of 3 or 4 wires on a bolt. trans or block. Those wires enter the harness thru splices behind the driver side valve cover where the harness is mounted to the firewall.
The braid cable is just ground between block and frame. Go thru the hot wires on the small terminal behind the battery called the jumper post. Those are the power supply for the ECM and cabin electrical. Those are not fused on the panel but have a fusable link under the battery. Has the MAP sensor been tested? or is this MAF? MAF has relays...IF its MAF then unplug it and see what happens. That will force a code AND make it run open loop. IF the spark is decent and the fuel burns, it'll run.
Fans...
I would take the green/why wire at the main fan relay and test for continuity at the ECM plug. IF that circuit is good to that point, the ECM can be suspect. Also, anytime the a/c is on with a charge and the compressor is running the main fan should come on via the a/c switch.
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Deal with this FIRST. Does the SES light ever turn on? (should turn on with just ignition on engine not running). Maybe the bulb is just bad. If it turns on with the ignition but does not flash when you jumper A and B of the ALDL connector then you have a major ECM problem to deal with before worrying about the fans.
Bill
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- #29
vernh
Member
Ses light does come on whith key in ignition it does go off once car is running. I have gotten the ses light to flash a few times by grounding a and b terminals. The only thing is it doesn't do like it is supposed to each time. Sometimes it will flash a few times fans and all will be running and it will just quit flashing and fans will go off. This made me think I have a short somewhere. So I have gotten it a few times to flash like it was supposed to and I began fondling all ground connections and all wires entering ECM to try and find the short and the darn thing wouldn't quit flashing. I ran the battery down to the point the fans wouldn't turn looking for a short. Also the only thing that would flash was 12. Should it matter that I did the check with the car heated up versus it being cold. That is the only condition I can think of that was different from when I couldn't get it to flash when jumpering versus it flashing when jumping. I wasn't able to get the jumper to work when car hot but it would workb some once car started cooling down.
boomdriver
Well-known member
three 12 flashes is normal.....then a pause....then 3 more 12 flashes then if nothing changes the same cycle repeats. Everything starts with 3- 12 flashes and ends with 3 code 12 flashes.
How about this......
Locate the ground wire/pin on the ECM plug and run a ground jumper to that and see if things suddenly work. IF they do NOT...might be saying the ECM is faulty.
assuming that you have pulled the center display bezels off and physically inspected the section of harness in the mid-dash toward the ECM...and its all OK,. start working your way toward the ECM and continue to do visual wire inspection.
A/C does not work? You can also PULL the a/c high pressure plug off the switch and the fans should run constantly. No matter if a/c works or not.
You DID locate and clean G-104 grounds....right? bundle of 14 gauge wires (4 or 5 wires) on a single bolt near oil filter??????????????????
THOSE are the most important grounds on the entire car....
How about this......
Locate the ground wire/pin on the ECM plug and run a ground jumper to that and see if things suddenly work. IF they do NOT...might be saying the ECM is faulty.
assuming that you have pulled the center display bezels off and physically inspected the section of harness in the mid-dash toward the ECM...and its all OK,. start working your way toward the ECM and continue to do visual wire inspection.
A/C does not work? You can also PULL the a/c high pressure plug off the switch and the fans should run constantly. No matter if a/c works or not.
You DID locate and clean G-104 grounds....right? bundle of 14 gauge wires (4 or 5 wires) on a single bolt near oil filter??????????????????
THOSE are the most important grounds on the entire car....
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- #31
vernh
Member
I have checked ground wire from ECM plug to location just behind oil filter and checked for continuity.wire checked good. Also have pulled ac pressure switch and fans wouldn't run. I just now tried to ground a and b with car not having run for a day and darn thing wouldn't go into diagnostic mode. I am leaning toward just buying another ECM to see if that is my problem. Car is hard to start. It does idle high with no service engine soon light on. And fans do not operate when they should. I also unhooked mad sensor and started car. It run really bad also with no ses light. I am just scared I will purchase another ECM to discover I still have the same problems.
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- #32
vernh
Member
Maf sensor. Not mad although right now I would call everything mad on this thing
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- #33
vernh
Member
ok guys just wanted to give an update and once again thank you all for your superb help and knowledge. I have traced all wires I could figure out and all check good continuity. I have determined I do have an ecm and or prom problem. I pulled ecm and looked for burns blisters or broken connections. Found none. did discover ecm has been changed before because the one in it is a remanufactured unit. Also, decided to reinstall and tap on it per a friends suggestion. no change. But I decided to leave prom access cover off. if i wiggle prom I get engine rpm to go up and down. I then decided to push on prom. rpm goes down to 700 rpm. I believe that to be correct. I then ground terminals a and b and push on prom it then goes into diagnostic mode and tells me error 15. Coolant temp. sensor. One question is that the sensor mounted in the front of the engine block? Also, one more question. Since I am not sure if problem is prom or ecm. Which I do believe it to be ECM. I am going to replace both. It was suggested I replace it with a hyped up chip. I don't believe much has been done to this car. I believe it to be mainly stock. Do I want a phase 1 or a phase 11 chip? Has anyone had problems with said chips? or do you guys recommend I stick with oem? Once again thank you all. I have already learned more in a month than I thought I would ever learn.
John Robinson
Gone but not forgotten
Yes the sensor on the front of the water pump is the one the code 15 is for. Now before jumping to conclusions that the ECM or PCM are bad start the engine and go shake the wires from the water temp sensor and the tps and anything else that has wires to it. The reason I say this is because 1 a code does not mean a bad part it only means the ecm is getting a bad signal 2 The signal is read from the ground wire not any other wire by the ecm. Since the TPS, Water Temp Sensor and about three other things all end up in a common ground bundle if that bundles grounds have be come corroded and the ecm is looking for information from those wires by a process of elimination it looks at all of them but if it is getting a weak signal from one it can only tell you that something is wrong with the signal from that particular circuit. The first thing to do is to test the TPS to make sure it is good because it has more control of the system than the politicians do of our debt. When you wiggle or press on something in the ecm it will react to that signal just because it is programmed to do so. It seems lately that we are beginning to see a failure of the wires in the wiring harness near the connectors that have been removed for normal service work over the life of the car. Finally you might try to use some spray contact cleaner to clean the connectors on the ecm that is another place corrosion will get in and mess up the ECM ability to work correctly and since you get some change in how the car runs when fooling around there it is suspect for corroded connectors. Be sure to disconnect the battery if you clean the connectors on the ecm.
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- #35
vernh
Member
John I have pulled all grounds and cleaned them. I also with ECM connected and in it's box wiggled every wire on the harness. I have checked ground wires to ECM for continuity as well as diagnostic wires back to ECM. I also unplugged Maf sensor and ran car with no check engine light on. The only way I get a check engine light is to run the car while applying pressure to prom. The only way I get car to idle properly is by applying pressure to prom. Also I have wiggled cleaned and jiggled every wire I could find to try and get it to run properly. I haven't cleaned contacts to ECM harness but I really am scared of introducing moisture to my wiring. Wouldn't a bad switch or wire show that fAulty by turning on check engine light? Also the only way I get it to go into diagnostic mode is by applying pressure to prom. Now I am confused. I really thought I had found my trouble.
John Robinson
Gone but not forgotten
I feel for your confusion and it does sound like you have tried everything. My concern for you is that I had a no start situation once that was diagnosed as the ecm and so I bought one only to find out it still would not start. I sure hated to look at that shiny new ecm and still not hear the engine run. In my case it was a faulty tps sensor that was not codeing. Since then I have chased bad idle and other bugs and codes until I finally replaced the wiring from the tps and maf sensor to the ground bundle and cleaned up that bundle. You may well have a bad ecm or prom but I was just wanting to make sure that you were not trapped into thinking it had to be the expensive stuff. It appears that you have done the leg work to maybe feel comfortable with your choice and I am anxious to hear about your success in fixing this problem.
boomdriver
Well-known member
Regarding the ECM< and maybe a new PROM...
I'd pull the current prom out and make sure all the pins are there not bent or broken. Bending them over is common when folks just shove the prom in without feeling it click or slide into the socket.
next, you CAN pull the ECM cover and look at the main board and see if there is a crack or some obvious simple defect. A simple solder job can sometimes fix it for good......Don;t get too worried...there are used ECMs available for less than $100...sometimes $50 . A rebuilt/exchange might be more but it will have some warranty. ECMs do not usually fail. When they do it can be difficult to diagnose but they usually don;t fail.
Prom...look for cracks or bad pins. As far as a replacement....The aftermarket PROMS are so generic that they only do so much for a semi-stock car. The programmer has no way of knowing exactly whats going on with your car, so they make the mass produced proms with a slight bump in the fuel vs timing curve, and IMO the only REAL useful tool in a generic aftermarket PROM is the "ThermalMaster" that makes the fans come on much sooner than the stock fan setting of 228 degrees unless a/c is running.
The Hypertech TM PROM turns the main fan on at 180 about...off at 162. When combined with a 180 thermostat you get cooler operating temps which amount to better performance. Otherwise, I'd wait to buy a PROM until everything else was done and running as it should. If you do exhaust, intake or other upgrades the prom is suddenly no good. You can get customs made that take your info and make your own prom. BUT< its only good for they way your engine is at that time.
I'd pull the current prom out and make sure all the pins are there not bent or broken. Bending them over is common when folks just shove the prom in without feeling it click or slide into the socket.
next, you CAN pull the ECM cover and look at the main board and see if there is a crack or some obvious simple defect. A simple solder job can sometimes fix it for good......Don;t get too worried...there are used ECMs available for less than $100...sometimes $50 . A rebuilt/exchange might be more but it will have some warranty. ECMs do not usually fail. When they do it can be difficult to diagnose but they usually don;t fail.
Prom...look for cracks or bad pins. As far as a replacement....The aftermarket PROMS are so generic that they only do so much for a semi-stock car. The programmer has no way of knowing exactly whats going on with your car, so they make the mass produced proms with a slight bump in the fuel vs timing curve, and IMO the only REAL useful tool in a generic aftermarket PROM is the "ThermalMaster" that makes the fans come on much sooner than the stock fan setting of 228 degrees unless a/c is running.
The Hypertech TM PROM turns the main fan on at 180 about...off at 162. When combined with a 180 thermostat you get cooler operating temps which amount to better performance. Otherwise, I'd wait to buy a PROM until everything else was done and running as it should. If you do exhaust, intake or other upgrades the prom is suddenly no good. You can get customs made that take your info and make your own prom. BUT< its only good for they way your engine is at that time.
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- #38
vernh
Member
Guys just wanted to let you all know I did replace my ecm. Fan now comes on in test mode. Car not running lean therefore exhaust not glowing after a few minutes. Also, it idles between 6 and 8 hundred rpm rather than 16 to 21 hundred per digital readout. Only thing now is when you start it if you just start it and do nothing else it will run for about 5 sec and then cut off. If you are ready to give it some gas and keep it running for about a minute it will then run and idle properly. Kind of a tricky thing to do since I have the entire interior pulled out. But after running for a few sec check engine light will come on and then i can turn it off and check the codes and it tells me i have a bad coolant temperature sensor. Once again I really appreciate each and everyone of your opinions and advice. Hope one day I may be able to return the favor.
vettegirl7
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What is the normal temp for these engines?
I just bought my 1989 vette a week ago and the temp runs about 185 to 197 while driving and then when i am setting still it will go up to 200 and sometimes up to 210 or 220, is that normal? Please help cuz i have no idea, I just got it and this is my first vette and I love it and I want it to run right! THanks in advance!
I just bought my 1989 vette a week ago and the temp runs about 185 to 197 while driving and then when i am setting still it will go up to 200 and sometimes up to 210 or 220, is that normal? Please help cuz i have no idea, I just got it and this is my first vette and I love it and I want it to run right! THanks in advance!
Hib Halverson
Technical Writer for Internet & Print Media
"Vettegirl7", your coolant temperatures are normal.
Good luck with your '89.
Good luck with your '89.
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