Occasionally, my Vette will start up, and run very rich. All that I have to do is open the hood, and drop it and it runs like normal. No check engine lights.

This happens about 1 in 10 starts. Sometimes, when I hit a bump (somewhat large bump it happens almost everytime I go over a certain bump on the way to my GF's house), it will run rich (the instant mpg gauge goes from 25 to 10) and then it will go away when the car hits another bump.

WTF? Loose connector somewhere? What sensor/connector would cause this? Its getting very irritating..

When it does it should I just open the hood and start tapping stuff lightly with a rubber mallet?

 

If you remove your master cylinder, you will expose a stroke adjustment screw. It may serve to move your peddle enough to solve your problem.

 

Sorry. Replied to wrong thread.:o

 

Is it a MAF or SD engine?

 

its a MAF engine.

 

next time it does it, rap the MAF sensor with a screwdriver handle and see if it clears up...

 

I hope its not the MAF, its not even 3 months old!

I will try this next time it does it.

 

MAF or O2 sensor.

And the MAF being three months old is suspect. Maybe you need to check the connector.

AND it could be a ground wire.

 

My first thought turned to the coolant temperature sensor screwed into the water pump. An intermittent connection there can cause all sorts of weird issues.

Next on my list would be one of the 02 sensors, but since they're so rigidedly mounted I wonder if the vibration from dropping the hood would effect it.

I recall that recently one of my son's 02 sensors failed (passenger side) and that bank of cylinders (2,4,6 and 8) went dead rich. Black smoke out of the tail pipe, etc.

When we pulled the spark plugs those four were black/sooty coal, yet the driver's side plugs were a beautiful light tan. $60 later for a new passenger side 02 and new plugs and all was well again.

Hope this helps.

Jake

West Point ROCKS!

 

Theres a CTS in the waterpump? I thought that there was only one in the intake manifold which i replaced already.

 

 

You have a LT1, right?

Jake

 

Just checked his profile, he has an 85. No CTS in the WP.

 

If there is a way to data log an 85 if that is what you have that would be the best way and probably the fastest way. If the milage display shows a change then it is a change the ECM knows about other wise it could not do the calculation to come up with a milage change. makes me doubt a bad ground bad fuel pressure regulator etc. It has to be a sensor input to the ECM to effect a change. If it were me lacking a data log I would start it up and start wiggling connectors you don't need to hit the parts hard if you go that route unless these bumps are big enough to bottom the car out. If this happens on a cold start i think you can rule out O2 sensor as well as it does not get into the picture until warm. I am also assuming the rpm on the tach does not change either. Given that you are down to MAF TPS coolant sensor air temp and TPS.. The last thing you worked on was MAF what made you change it the same or similar problem? Is it new or 'rebuilt' or used off another 85? I am not sure but think there are 2 relays for the MAF I have a SD car so unsure but thought 1 for burn off and 1 for the hot wire while running. If that gets flaky and the wire cools off i would think the ECM would think the air flow has changed and add fuel.. Just some thoughts. Like I said a scan tool or data log it would show up quick. Hook up the logger and go hunting for pot holes..LOL If you live in NE like I do it will be a short search...sigh..
Dave

 

It does it when its cold, so i guess that rules out the O2 sensor. The MAF, TPS, IAC, are all less than 6 months old.. they were replaced with new units. (maf was rebuilt, but it is a bosch rebuilt unit).

From what I know, 85's are special and came with burn off modules for the MAF..its a little box up by the ecm that controls burnoff. I don't know if it could be tested some how or not.

Does anyone know if you can datalog an 85?