85 Running Rich - Possible Causes?
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
85 Running Rich - Possible Causes?
My 85 has started running way too rich - failed emissions with the CO 5 times the allowable limits. My LM-1 A/F gauge shows the car running at about 12.5:1 to 13:1 at cruise. Obviously, way out of whack. On cold start-up, idle is rough and extremely rich - will not maintain idle without keeping foot on gas.
The injectors are near-new. I just replaced the TPS and set it up correctly. Injectors and TPS did not affect the CO levels. I have a new ox sensor to install, but I don't think this will solve the problem. No error codes are showing up.
Other than replacing the ECM and the MAF, you guys have any ideas on things to check and do to lean this thing out? The problem occurred suddenly, so there is something that has failed. Just can't seem to locate the bad component. Any suggestions and ideas would be great!
The injectors are near-new. I just replaced the TPS and set it up correctly. Injectors and TPS did not affect the CO levels. I have a new ox sensor to install, but I don't think this will solve the problem. No error codes are showing up.
Other than replacing the ECM and the MAF, you guys have any ideas on things to check and do to lean this thing out? The problem occurred suddenly, so there is something that has failed. Just can't seem to locate the bad component. Any suggestions and ideas would be great!
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Good point - I had that happen on an 82 Crossfire car. However... does the ECM receive engine temp data from the same sensor as the water temp gauge? Or is there a separate temp sensor for the ECM like Saturn does? My water temp gauge reads normal - not low. But if there is an ECM-dedicated sending unit, this could be the cause. Does anyone know?
Racer
Joined: May 2006
Posts: 293
Likes: 0
You have the ECT sensor in the front of the intake manifold for the ECM. But that isn't likely the problem. If it were bad, your cold idle would be better, if not ideal. A vacuum leak or a diverer problem for the A.I.R. system, are strong possibilities. There is a section for trouble shooting this very problem in your FSM.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
I have the Service Manual, and I found the section on troubleshooting a rich condition to be not very helpful. I'll check the AIR diverter - the pump itself was recently replaced, and I've done the usual checks for vacuum leaks and common problems (cracked hoses, PCV, broken Ts & fittings, etc.). 
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
I'm going to pop my new one in tonight and see what happens. Did your engine go rich when the sensor failed..? My concern is that I'm running extreme rich on intial cold start as well as running rich at cruise after warm-up. The ox sensor does not provide input to the ECM when in open loop (cold engine), yet I have an extreme rich problem when cold.
Melting Slicks
Joined: Nov 2002
Posts: 2,471
Likes: 2
From: 1993 Quasar Blue 'vert Scottsdale AZ
Yes, mine ran rich. It's still running rich (but at least it now stays in closed loop) and I believe that it may be a problem with the Air pump system. I'm going to have it checked out next week because emissions-testing time is approaching.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
My 85 has started running way too rich - failed emissions with the CO 5 times the allowable limits. My LM-1 A/F gauge shows the car running at about 12.5:1 to 13:1 at cruise. Obviously, way out of whack. On cold start-up, idle is rough and extremely rich - will not maintain idle without keeping foot on gas.
The injectors are near-new. I just replaced the TPS and set it up correctly. Injectors and TPS did not affect the CO levels. I have a new ox sensor to install, but I don't think this will solve the problem. No error codes are showing up.
Other than replacing the ECM and the MAF, you guys have any ideas on things to check and do to lean this thing out? The problem occurred suddenly, so there is something that has failed. Just can't seem to locate the bad component. Any suggestions and ideas would be great!
The injectors are near-new. I just replaced the TPS and set it up correctly. Injectors and TPS did not affect the CO levels. I have a new ox sensor to install, but I don't think this will solve the problem. No error codes are showing up.
Other than replacing the ECM and the MAF, you guys have any ideas on things to check and do to lean this thing out? The problem occurred suddenly, so there is something that has failed. Just can't seem to locate the bad component. Any suggestions and ideas would be great!
I found the AIR switching (closest to the A/C compressor was bad)
to check, pull the hose off from the soleniod that faces the engine, this is the hose that supplies the air to the exhaust manifold. If you pull this off and there is still air blowing out whe your car goes closed loop then
this is a major contributor to you running rich, there should be no air coming from it when you are closed loop. Now, have you read any codes from the ECU? you really have to start there.
Tom
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Tom -
Thanks for the tip - I'll check that tonight. I have no trouble codes stored - I keep hoping for something to fail bad enough to set a code, but I show "all is well."
Thanks for the tip - I'll check that tonight. I have no trouble codes stored - I keep hoping for something to fail bad enough to set a code, but I show "all is well."
Racer
Joined: May 2006
Posts: 293
Likes: 0
Originally Posted by lars
My concern is that I'm running extreme rich on intial cold start as well as running rich at cruise after warm-up. The ox sensor does not provide input to the ECM when in open loop (cold engine), yet I have an extreme rich problem when cold.
Last edited by C4Techie; Mar 1, 2007 at 02:49 PM.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
I agree. Any thoughts, then, where the issue could be? I'm going to replace the ECT sensor, since it does provide ECM input in open loop - when the sensor went bad on my 82 Crossfire, the engine ran extremely rich, even when cold - just like this one is doing now. But I'm not sure where else to start looking with no trouble codes and the over-rich condition in both closed and open loop...
Melting Slicks
Joined: Aug 2003
Posts: 3,401
Likes: 397
From: Lakeville MI
Check the fuel pressure regulator to be sure fuel isn't leaking past the diaphragm and being pulled into the intake through the vacuum port.
Also check the fuel pressure while your at it.
MAF is also suspect and is the primary signal input for fuel delivery in both open and closed loop modes.
The ecm has only a limited ability to reduce excessive fueling in closed loop (BLM lower limit is 108)
Also check the fuel pressure while your at it.
MAF is also suspect and is the primary signal input for fuel delivery in both open and closed loop modes.
The ecm has only a limited ability to reduce excessive fueling in closed loop (BLM lower limit is 108)
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
[QUOTE=tequilaboy;1559183411]Check the fuel pressure regulator to be sure fuel isn't leaking past the diaphragm and being pulled into the intake through the vacuum port.
/QUOTE]
TB,
How do check for the above conditions?
Thanks,
Tom
/QUOTE]
TB,
How do check for the above conditions?
Thanks,
Tom
Racer
Joined: May 2006
Posts: 293
Likes: 0
If the ECT sensor circuit is fully open, the ECM will see the temp as -40 F. That will cause the ECM to fatten up the mixture, but rather than throw money at it, why not test the ECT sensor?
Melting Slicks
Joined: Aug 2003
Posts: 3,401
Likes: 397
From: Lakeville MI
Disconnect the vacuum line at the regulator and plug the open end of the hose with a golf tee or something.
Removing the vacuum from the regulator will raise the fuel pressure by a few psi, but will eliminate the flow path for fuel into the intake plenum, if it is leaking.
How does the car respond? If there is no leak, it should run slightly richer due to the increase in fuel pressure.
If there is a leak, it should run leaner, but the rise in fuel pressure will also have a bit of an offsetting enrichening effect.
You may also see fuel dripping from the open port on the regulator, if it is bad enough.
Another option would be to use a clear line to replace the normal black vacuum hose and watch to see if any fuel is flowing into the intake when running. I think a fairly long length of clear tubing coiled up will make it easier to see if it is filling with fuel. This method may be safer if you have a big leak to avoid fuel spillage.
You could also apply vacuum to the regulator with a hand pump like a miti-vac and see if it is pulling any fuel.
Removing the vacuum from the regulator will raise the fuel pressure by a few psi, but will eliminate the flow path for fuel into the intake plenum, if it is leaking.
How does the car respond? If there is no leak, it should run slightly richer due to the increase in fuel pressure.
If there is a leak, it should run leaner, but the rise in fuel pressure will also have a bit of an offsetting enrichening effect.
You may also see fuel dripping from the open port on the regulator, if it is bad enough.
Another option would be to use a clear line to replace the normal black vacuum hose and watch to see if any fuel is flowing into the intake when running. I think a fairly long length of clear tubing coiled up will make it easier to see if it is filling with fuel. This method may be safer if you have a big leak to avoid fuel spillage.
You could also apply vacuum to the regulator with a hand pump like a miti-vac and see if it is pulling any fuel.
Team Owner
Joined: Jan 2003
Posts: 20,322
Likes: 248
From: Summerland B.C. Canada
[QUOTE=tdr1919;1559184895]
Pull the FPR vac line and check it for fuel. 
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
It has now suddenly cured itself... Only occasionally and intermittently will it now run rich. Last 2 cold starts were normal and had acceptable A/F ratio when cold, and cruise mixture suddenly corrected itself from 13:1 to 14.5. But I just did another cold start moments ago, and it flooded itself out and puked rich until I shut it down and did a re-start. Then ran normal again. Still no error codes being set.... This thing is going to drive me insane.