1985 C4 running rich
Thread Starter
6th Gear
Joined: Dec 2019
Posts: 6
Likes: 0
1985 C4 running rich
Hello Everyone, I have a 1985 Corvette. I bought the car 2 years ago. I had the engine rebuilt last summer, every since I put the engine in the car runs rich. I hooked up my code reader and it said coolant temp. sensor. I have replaced both of the sensors twice and it's constantly running rich. I replaced the fuel pressure regulator, ECM, IAC, TPS, Injectors, fuel pump, gas tank, and New Distributor. I removed and clean the grounds. Any advice would be helpful. Thank you in advance
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
Hello Everyone, I have a 1985 Corvette. I bought the car 2 years ago. I had the engine rebuilt last summer, every since I put the engine in the car runs rich. I hooked up my code reader and it said coolant temp. sensor. I have replaced both of the sensors twice and it's constantly running rich. I replaced the fuel pressure regulator, ECM, IAC, TPS, Injectors, fuel pump, gas tank, and New Distributor. I removed and clean the grounds. Any advice would be helpful. Thank you in advance
Last edited by KyleF; Jun 1, 2020 at 04:57 PM.
Thread Starter
6th Gear
Joined: Dec 2019
Posts: 6
Likes: 0
What makes you think it is running rich? Black smoke and had to replace plugs a coupe of times because they were wet, and had to change the oil because it smelled like gas. What is your Fuel Pressure 40 and drops to 20 as soon as to turn off the ignition, What are your BLMs, IAC counts I have to check those, TPS Voltage 5.4? Etc. I noticed the one part on your list that is missing is the 02 Sensor I haven't replaced the O2 it was replaced right before I got the car. What voltages is the ECM seeing from it? Not sure
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
What makes you think it is running rich? Black smoke and had to replace plugs a coupe of times because they were wet, and had to change the oil because it smelled like gas. What is your Fuel Pressure 40 and drops to 20 as soon as to turn off the ignition, What are your BLMs, IAC counts I have to check those, TPS Voltage 5.4? Etc. I noticed the one part on your list that is missing is the 02 Sensor I haven't replaced the O2 it was replaced right before I got the car. What voltages is the ECM seeing from it? Not sure
Last edited by KyleF; Jun 2, 2020 at 08:13 AM.
Melting Slicks
Joined: Jun 2014
Posts: 2,226
Likes: 497
From: NJ
Not sure of this but, does this engine have a separate cold start injector? This could be a problem. Also, I did notice your fuel press. drops off quickly at shutdown, indicating a fuel leak possibly from the cold start injector. But here again, don't know enough about this model year to give you a definite answer. Just trying to help.
Thread Starter
6th Gear
Joined: Dec 2019
Posts: 6
Likes: 0
Not sure of this but, does this engine have a separate cold start injector? This could be a problem. Also, I did notice your fuel press. drops off quickly at shutdown, indicating a fuel leak possibly from the cold start injector. But here again, don't know enough about this model year to give you a definite answer. Just trying to help.
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Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
It too could be leaking, which was a good point.
This would be a situation where the O2 Volts would be high (Rich), BLMs would be low (Pulling Fuel) but you have and obvious rich condition with the plugs.
Oil Producer
Joined: Apr 2014
Posts: 9,365
Likes: 2,734
is the engine stock? i understand its been rebuilt but is it a stock rebuild?
85’s were 24lbs injectors, not 22. this may be causing the o2 to see lean condition which causes the ecu to request more fuel this creating the rich condition.
Do you have a laptop computer, an aldl cable (aldlcable.com i think is where i purchased mine) and and a volt meter?
Last edited by VikingTrad3r; Jun 4, 2020 at 11:10 AM.
Oil Producer
Joined: Apr 2014
Posts: 9,365
Likes: 2,734
i re-read your first post. u have sure tossed alot of parts at it.
id get the aldl cable.
i have a caveat for you with the aldl cable. on the 85, and only the 85, the aldl connection is a tad less useful than with the 86 and up. But for the purposes of what you are trying to solve here, it will still give u what you need.
the tunerpro rt with aldl combo is very useful once it has been setup. its not exactly plug and play....so when u get it, google how to set it up and if/when u have trouble post here and we can help u.
i recently fixed my 87 which was also running rich and through a series of tests it was easy to see what the issue was. in my case the o2 sensor was giving whack values of 0-5mv!
Thread Starter
6th Gear
Joined: Dec 2019
Posts: 6
Likes: 0
i re-read your first post. u have sure tossed alot of parts at it.
id get the aldl cable.
i have a caveat for you with the aldl cable. on the 85, and only the 85, the aldl connection is a tad less useful than with the 86 and up. But for the purposes of what you are trying to solve here, it will still give u what you need.
the tunerpro rt with aldl combo is very useful once it has been setup. its not exactly plug and play....so when u get it, google how to set it up and if/when u have trouble post here and we can help u.
i recently fixed my 87 which was also running rich and through a series of tests it was easy to see what the issue was. in my case the o2 sensor was giving whack values of 0-5mv!
id get the aldl cable.
i have a caveat for you with the aldl cable. on the 85, and only the 85, the aldl connection is a tad less useful than with the 86 and up. But for the purposes of what you are trying to solve here, it will still give u what you need.
the tunerpro rt with aldl combo is very useful once it has been setup. its not exactly plug and play....so when u get it, google how to set it up and if/when u have trouble post here and we can help u.
i recently fixed my 87 which was also running rich and through a series of tests it was easy to see what the issue was. in my case the o2 sensor was giving whack values of 0-5mv!
Safety Car
Joined: May 2001
Posts: 4,749
Likes: 1,642
From: Fairfax Virginia
If your Oxygen sensor is over 24 months or 50k miles then replace it as that was all they were made to do. When the fail they like to fail rich so the engine is not damaged.
Contrary to what some believe these sensors were designed for only 24 months or 50k miles, As they age they send a smaller (narrower) signal and they lag behind the computers need for information which can cause drive ability issues.
Left running too rich the catalytic converter will fail as well.
The Cold Start Injector has wires that power the injector and on my 1988 C4 you can disable it by disconnecting the wires. That doesn't help when you have a leaking cold start injector which can happen like other injectors.
I bought an Older Snap On MT2500 which was a nice scanner in it's day. It provides a wealth of information on my 1988 and my other newer OBD2 vehicles. The best part is that Bosch made a cartridge with Snap On for the Bosh ABS systems the early C4's came with. It allows you to test and verify that the parts are actually working. I have about $300 in the whole kit. Tuner pro is on my horizon but I have not purchased the cables needed to make it work.
Contrary to what some believe these sensors were designed for only 24 months or 50k miles, As they age they send a smaller (narrower) signal and they lag behind the computers need for information which can cause drive ability issues.
Left running too rich the catalytic converter will fail as well.
The Cold Start Injector has wires that power the injector and on my 1988 C4 you can disable it by disconnecting the wires. That doesn't help when you have a leaking cold start injector which can happen like other injectors.
I bought an Older Snap On MT2500 which was a nice scanner in it's day. It provides a wealth of information on my 1988 and my other newer OBD2 vehicles. The best part is that Bosch made a cartridge with Snap On for the Bosh ABS systems the early C4's came with. It allows you to test and verify that the parts are actually working. I have about $300 in the whole kit. Tuner pro is on my horizon but I have not purchased the cables needed to make it work.
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
is the engine stock? i understand its been rebuilt but is it a stock rebuild?
85’s were 24lbs injectors, not 22. this may be causing the o2 to see lean condition which causes the ecu to request more fuel this creating the rich condition.
Do you have a laptop computer, an aldl cable (aldlcable.com i think is where i purchased mine) and and a volt meter?
85’s were 24lbs injectors, not 22. this may be causing the o2 to see lean condition which causes the ecu to request more fuel this creating the rich condition.
Do you have a laptop computer, an aldl cable (aldlcable.com i think is where i purchased mine) and and a volt meter?