GTc4

Should the 1985 L98 run with the MAF unplugged?
With my car running if I unplug the MAF connector the car dies straight away, no puter or hesitation just dies as key turned off is this right?

I read all the post stating unplug mass airflow sensor to see if changes this or that but mine will not run with it unplugged!

Should have stated my problem ....hunting for Idle and running fairly rich but has no starting problems at all turn key and it fires first turn no joke that has me baffled usually if car runs rich like this one is it is hard to start!??

Timing is right on at 6 Deg BTDC, new plugs and wires, cleaned maf, set timing by FSM, new air filter

The car runs rich from start up in open loop and when at operating temp in closed loop!

Just bought car few weeks ago PO stated the injectors were new, match ported intake runners, distributor cap and rotor were new, has Coarse exhaust cat-back, also computer chip was updated ... I don't know the brand or stage??

Any info would be appreciated!! HELP PLEASE!!!

c4_4ya

When I had my 85 it did the same thing when the MAF was unplugged... immediate shut off. The coolant temp sensor on the front of the intake, if bad, can cause it to run rich (this is NOT the sensor that feeds your temp gauge).

Inconsistent idle is commonly remedied by cleaning or replacing the TB or IAC, adjusting the TPS, or caused by a vacuum leak. Also check the size of the injectors, IIRC 85 stock injectors are 24#; if they are now bigger then the custom chip may not be tuned correctly for the new injectors and/or fuel pressure.

84wuzmy1st

My 85 runs a little rich, especially at start up and when cold.

Mine also hunts a little for idle, but not all the time and just barely. How often and how badly is it hunting?

leesvet

why would you go straight to the MAF ?????

do you have DTCs that indicate a MAF malfunction?

to answer the question, yes, the engine will die immediately if you unplug the MAF when running. YOU are NOT SUPPOSED TO DO THAT.

That's very hard on the ECM. It does not like "shock treatments"...

You are supposed to unplug the MAF THEN start it. It will be hard to start but it WILL start and eventually see there is a problem and the ECM will shift modes to its programming and run fine. The SES will come on and it will set and store the code.

Unless you see a MAF code displayed, don't mess with the MAF unless you have money to spend on new ones...they ain;t cheap. That plug is more fragile than the MAF so handle it gently. The wires break inside the plug and its junk.

Rich idle, fuel comes from a million other places. o2 sensors, coolant temp, injectors that are TOO big is what I suspect. People treat these engines like the 'ol chevy SB from 1970 and start sticking bigger parts on thinking bigger is better...its NOT. The computer has to be "tuned" to accept changes in parts. You state there are new injectors...they may be too big. People think that putting bigger injectors in automatically makes more power. It does not. ALL that does is foul plugs and wear out the engine sooner from the rich fuel in the cylinder washing the oil off the rings and walls...
Rich is not good.

Try to find the cause of this. if it is injectors that are bigger it can be "tuned" to handle it. If its a sensor issue, that can be fixed.
IIWM, I'd get the fuel pressure readings, and look at any stored codes and go from there. of course check all EFI plugs under the hood for clean and contact. Pull a couple randon spark plugs to look at the color. That will tell you if its dangerously rich or just a little off.

That's a nice looking car. I'm sure there is nothing seriously wrong, just a matter of some maintenance.

aklim

If you can pull an injector and read the numbers, Jon at FIC might be able to give you an idea of what the poundage is. Once we know that, the programmer can change the tune. I wouldn't get a canned tune which is "one size fits all". I have always used tunes written for my vehicle. Best would be dyno or datalog.

vetteoz

As noted above , have you pulled the engine error codes to see if the ECM is trying to tell you something ?

http://www.corvettephotographs.com/c4vettes/codes.htm

How do you know the car is actually in CL?

GTc4

yes when I got the car it had 33 and 34 set thats why I suspected the MAF but now believe they were ghost codes from years past ses light is not and does not come on after car is started bulb is good comes on before start!

have changed plugs and wires, set timing to be sure!

I will looks like pull injectors to see what they are and try to find someone to burn me chip to match them PO stated they were new and chip has been changed in the past

GTc4

Thanks did have 33 and 34 cleared codes and none have returned,
installed new plugs and wires and have pulled the new plugs to inspect and double check my work they are wet with fuel! but to be expected running rich
It does this in closed and open loop.
It hunts for ideal why I think it may be air issue am I correct here?

GTc4

had 33 and 34 when i got the car cleared all codes got 42 when set/checked timing cleared it and no codes or ses when running light is good by the way checked it works fine!

Isn't it in closed loop when at operating temperature ?

The car runs great even though it has this rich situation and hunts for the idle...... its a 4+3 ... idle at 700-800 when idling but all over the place between 700 and 800!

vetteoz

It is "supposed "to go CL when certain parameters are met like correct temp and seeing the O2 sensor come on line.
The engine being at that temp does not mean the ECM has actually engaged CL

Throwing a scanner on it will give a better indication of what it is doing and why

leesvet

if your plugs are WET with fuel, you have OTHER problems.
That's not RICH....That's FLOODING.
That will destroy the engine.

Black LS2

After nearly 20 years messing with intermittent issues with the MAF, the exact same codes you get, once in a while CEL, and nearly the same ocassional symptoms (except for the spark plugs), I sprung $35 on eBay for the two Delco 14089936 MAF relays on the firewall of my 87. Best $35 I have ever spent on a vette.

Turned out that he ECM was looking for the relays to juice the MAF burn off wire in certain amount of time, and while the relays worked fine and tested fine, one of them did not work fast enough.

GTc4

I probably overstated by saying wet they have a damp look too them .....
I don't like my vehicles running wrong flooding its not..... running rich it is!

Cliff Harris

Mine will die right away if the MAF is unplugged while the engine is running.

If you disconnect it while the engine is NOT running then it will start and run (sorta normally). The ECM uses the TPS to guess what the air flow is.

Cliff Harris

Depends. The O2 sensor has to be hot enough to work for it to go closed loop. That may never happen if you have problems (like unheated O2 sensors in long tube headers).

If you are running rich, that can be caused by a bad CTS (Coolant Temperature Sensor) or a bad connection to it. The ECM uses the CTS on the front of the engine. If the ECM thinks the coolant is cold it will richen the mixture like the choke did on a carburetor.

The extra fuel causes the mixture to be rich so the ECM adds air. Then the RPM goes up so the ECM backs off on the air. It goes back and forth and you get the wandering idle symptom.

GTc4

changed cts already! no change ....

Cliff Harris

The only way to see what is really happening is to scan the car and find out what the computer is seeing. A handheld scanner can do this or use a cable and scanner software.