87 vette running pig rich at idle and stalling every time I push the clutch in to stop. Plugs are black and you see and smell it rich at idle out the mufflers. Replaced mass air flow sensor , idle air control and the plug ,and changed the coolant temp sensor in front of intake and put a new plug on for it to , and new tps sensor and volts set correct. Still rich . The question is if I let it warm up and unplug the coolant temp sensor in the front of the intake shouldn't the engine rev up from dumping fuel?? The idle don't change or does the exhaust fumes. I'm leaning tord that my ecm has gone bad not reacting to the coolant temp sensor being unplugged. Thanks for any advice . Been a real pain in the *** and can't find anyone with or able to find one to bye a obd1 scanner

 

Have you checked the 02 voltage, bad 02 sensor can throw a rich condition. Now a scanner have you given a look at apps or web pages like Let Go or offer up. I found a basic OTC good for the early cars for $50. and a snap On 2500 with all cable's and cartridges for $125

 

Sorry I forgot to mention new o2 sensor too

 

When my CTS went bad it keep the motor too rich when it warmed up so would run like crap and stall. When unplugged it would just take longer to start when cold but run normal when warmed up.

 

I have cold hard starts but never tried to run it down the road unplugged . It's a tpis mini ram intake so no ninth injector but I didn't have promblem with hard cold start when I first installed the intake. So that's why I'm thinking my ecm went bad . If unplug the cts it doesn't try to change idle it stays the same. Shouldn't the engine rev and dump fuel cause it thinks the engine went cold?

 

I ran my 91 for a few weeks with the CTS unplugged until i could install a new one. Idle may have been a bit elevated with CTS unplugged, but not too high. Right after installing the CTS the MAP sensor started acting up which did cause idle issues.

 

I'm really hoping someone on here can chime in that's had a bad ecm and what type of problems they had

 

What brand MAF did you buy?

 

Pretty sure Delphi I would have to go out to the garage the box is still on there

 

When my ecm went bad, i had a high idle for about 10 minutes when cold.
the mileage was waay off on mpg and range.
then 10 minutes later, the numbers were Kinda what i had the day before, nice idle, and smooth
ran fine, then next morning, same thing all over again.
i thought it was the maf, then O2 sensor, then bad gas.
a friend of mine loaned me his computer out of a buick, and i used my eprom, it didn’t run funny when cold.
so i got a used one from A guy on the camaro forum.
its still in there, 20 years later.
the eprom is out of an 89 corvette with auto and 307 gears.
works great.

 

I definitely have horrible gas mileage. Like said before it can be 85 degree outside and engine warm and you can see it running rich out the mufflers and smell it extremely Rich. Plugs look horrible to.

 

Crazy idea here. Check the scanner and see what it thinks the CTS says and hit the CTS with an IR Thermometer and see if that is right.

 

Great idea but I can't get my hands on a odb1 scanner. I'm goin to ask around when I'm at work today and see if anyone knows where I can borrow or even bye

 

1320 electronics, ebay for the Snap On MT2500.

 

Got scanner hocked up finally it it's reading it's stuck in open loop . Any suggestions would be great
I read over at a third gen site you have to run a heated 02 sensor when running headers. Anyone ever heard of this?

 

It's possible. I believe there are other conditions that can stick it in open loop.

 

I just got off the phone from mark at PCM of NC who did my chip. First thing he asked me after I told him what's goin on was if I was running a heated 02 sensor . Any one else running a heated o2 sensor with headers ???

 

Hello there Brandonvette,

For a Corvette to get stuck in "open loop" one of the three primary components is defective or not connected.

In "Closed Loop" your Oxygen Sensor is one of the most important sensors. Followed by the MAF or MAP sensor and last but not least is the Coolant Temperature Sensor.

The heated oxygen sensor is there to help the car stay in "closed loop" at long stoplights where a non-heated O2 can cool off and turn off allowing the car to return to open loop mode. It is not making any problems for you most likely. I have a heated sensor on my 1968 C3 427 with long tube headers and have no issues. The heated O2's are used primarily to reduce emissions and make a faster transition from open loop to closed loop while the Corvette is warming up.

Take a few minutes and using a Multi meter you can verify that the components listed above are working. The O2 is supposed to oscillate back and forth from .1 to .9 Vdc. Your Meter might average it out as the signal is extremely fast. An Older O2 will read between .2-.7 in place of the wider range when it was new. If the O2 is over 24 months old then just replace it. The life expectancy for the OBD1 cars Oxygen sensors was 24 months or 50k miles. It doesn't matter whether the Corvette was run during the 24 months prior as they corrode quickly. THIS does not mean that they can't last longer than the 24 months or 50k miles as they can and do sometimes. If the O2 fails then the Corvette will be locked into "Open Loop" and that puts the car in a low power safety Limp-Home mode. Ask me HOW I know this.... Also we have seen more O2's fail "Rich" versus Lean which could hurt the engine.

The CTS is an important sensor as it affects the Air/Fuel ratio the engine gets. If the CTS thinks it is hotter than it really is the car will not start easily as it will withhold Fuel Enrichment to start the engine. If the CTS thinks it is 20* (F) then it will activate the fuel enrichment which acts like a choke on older cars. If this happens to a Corvette it will make the Corvette run very rich and your plugs will be black. It is critical that the CTS is accurate and connected. I have seen corrosion on the connectors to the CTS that caused wacky readings.

The MAF sensor is different than the MAP sensor but they both do the same job in different ways. Their job is to measure the volume of air being ingested into the combustion process. If there are any leaks in the tubes between the MAF and the Throttle body the MAF can not accurately measure the air volume correctly. I had a MAP sensor fail on my DD a few months ago and it would cause the car to miss while under loads like going up a hill.

From re-reading the posts previous to this I would guess that your O2 might be the issue as it is fairly common. It would do the rich running if the sensor was bad normally. Is it safe to assume that you have checked your Fuel Pressure regulator to be sure it is not the source of your trouble? Simply disconnect the hose and smell for gasoline, if the smell is there then you need to replace the diaphragm in the Fuel pressure Regulator.

I see that you replaced the Oxygen sensor. I bought four at one time and one was bad from the factory and these were the Bosch brand. There is no guaranty that your new one works right out of the box. I buy my O2's from a NAPA Warehouse where they sell a bunch of them so I assume they are fresher. The O2 sensor is able to be poisoned by excessive oil burning and other contaminants in the engine oil.
One thing you are doing is destroying the catalytic converter as the rich running causes them to plug up faster.

Try another O2 sensor and see if that helps you. ECM's do occasionally go bad with cold solder joints and other issues but it is not so common that I would start there. Exhaust all other possibilities before messing with your ECM. About 22 years ago I bought a set of testing rigs for the EFI sensors from Mid America. They basically plug into the O2 and have extra wires to allow you to see what the sensor "sees" and this makes setting the TPS and verifying the rest of the sensors are within range. The set cost about $100 and has saved several C4 owners some trouble by making the system easy to check out. They helped me identify the bad Knock sensor I had that was retarding the timing a bit too often.

Take a few minutes and tell us about your car in the "Profile" section, this eliminates a lot of questions as it allows us to know what you are dealing with. Include all modifications to the original systems.

 

I put a new remain ECM from Rock Auto in it to and still rich. When I stop and sit for a moment is when you see it go rich and smell it out the pipe but running down the road the car runs strong so I'm wondering if the 02 sensor is cooling off then goin open loop again. Yes I checked the fuel pressure regulator and no gas in the valcum lines. I even turned the fuel pressure back ten psi to see if if doesn't go rich as bad and it still doesn't change the excessive fuel dumping
O and the 02 sensor did come from Napa

 

Try a heated O2 sensor. I just changed mine after 5 years.