Help! Bad MAF

[Marv02]

Will a bad MAF keep my car from starting I unpluged I still can't get the car to start.
The ownner of the Local Napa store told me his C4 would not start due to a bad MAF.

 

[Ripp 73]

When you say you can't get it to start, is the engine not even turning over?

The Mass Air Flow Sensor tells the engine how much air to bring into the intake, if it does not have that information, your engine can do a wide variety of things. If the engine is cold, it could idle high and then kill itself, or vary between a high idle and a low idle to the point where it wants to stop but kicks up into a higher rpm again, if the engine is warm, it may run for a second or two, and then stop, or it may not run at all and just crank.

If you do get the Corvette to run long enough without the MAF sensor connected, your CEL will come on shortly.

 

[Marv02]

I just put a new motor in the car It will turn over but it willn't start and yes It in time yes I put the motor on TDC yes I have good compression Yes I have good white spark.

And yes the valves are opening and closing timming is good.

When you say you can't get it to start, is the engine not even turning over?

The Mass Air Flow Sensor tells the engine how much air to bring into the intake, if it does not have that information, your engine can do a wide variety of things. If the engine is cold, it could idle high and then kill itself, or vary between a high idle and a low idle to the point where it wants to stop but kicks up into a higher rpm again, if the engine is warm, it may run for a second or two, and then stop, or it may not run at all and just crank.

If you do get the Corvette to run long enough without the MAF sensor connected, your CEL will come on shortly.

 

[Jeb]

Will a bad MAF keep my car from starting I unpluged I still can't get the car to start.
The ownner of the Local Napa store told me his C4 would not start due to a bad MAF.

What makes you think it's the MAF sensor? Just the guy at NAPA?

 

[TedC]

If you feel the MAF is causing the issue, then disconnect and try restarting. With the MAF disconnected, the ECM will use default settings. Understand that using default ECM settings will allow the engine to run, but it can run real rough. If the engine starts and runs with the MAF disconnected you should expect the ECM to post at least one error code. If you get the engine to run, then back probe the purple wire to make sure you have a 12 volt supply coming from the MAF power relay.

Why do you think this is a MAF issue? If the compression and timing are right, spark is right, I would focus my attention on the fuel side. Fuel pressure, resistance values at each injector (looking for a short), injectors being pulsed by the ECM, even the smell of raw gasoline on the plugs or from the tail pipes. Is your TPS adjusted properly?

 

[Marv02]

The Napa Guy said his did the same thing would not start and yes It what the Napa guy said.

What makes you think it's the MAF sensor? Just the guy at NAPA?

 

[vetteoz]

If you get the engine to run, then back probe the purple wire to make sure you have a 12 volt supply coming from the MAF power relay.

On another Forum he states he thinks his pump relay is bad.
When pump relay closes it sends power to fuel pump and closes the MAF power relay at same time
If the pump relay is not operating there will be no power to the MAF power relay so he will have no MAF signal at all

 

[boomdriver]

Looking back...

Blue is more the ideal spark color I think, and should be audible as a crisp quick click. You can't read plug fire thru a spark plug tester. has to be with a plug out and well grounded.

Is it possible that a wire inside the distributer was pinched under the cap? happens everyday. Also, there are many aftermarket ign modules that are JUNK that won't produce enough energy to generate a good hot spark. Weak spark, no combustion. A spark CANNOT jump across the electrode under compression if the spark is weak in any way.
Delco ignition modules are calibrated for the vette. Aftermarket parts often have looser spec for other applications to help offset cost and increase profits. Thats why Delco electronics cost more.

Next, if the MAF were sitting on the table, the car should still start and run with some burping for a few seconds until the ECM set in the open loop Limp-Home mode. That will allow engine operation with minimal sensor input. Mine ran foe days without the MAF and ran fine whiloe stuck in OpenLoop.

You;re probably a couple steps ahead of the napa guy... but going back over basics can;t hurt.

 

[TedC]

Blue is more the ideal spark color I think...

Agree. I use a spark tester that you set the gap to match the coil output voltage you want to test. The stock L98 coil has no issue jumping the tester regardless of the gap I set. Spark is strong with a blue color. The delco coil used in L98 vettes is a high output coil.

 

[Marv02]

Put power to the G spot the Fuel pump is working great so now I know I have a bad relay once again so I oreded one of them and a new pig tail for it.
The plugs are comming out wet so I know I getting fuel.
I going to pull the pulgs once again and put the motor back on TDC put a screw drive down the spark plug hole just to make sure TDC on the balencer mark is TDC for the compression of #1 cylinder.
I had a Trans Am many years ago that the balencer went bad and when I replaced it with a new one I now remember the timing marks were way off after that.
I remembered this last night at 2:00 AM LOL So I do the touch the pistoin trick with a screwdriver to make sure the timing marks on the New balencer are correct.
I read some where there old style balencers and new style on of the key ways on the crank sits at 12:00 at TDC and the Other is set at 2:00 position I did think about this untill last night either. The motor thats in the car now it a 1968 to 1978 I think 2 piece rear main seal driverside dipstick 4 bolt main.
I had to change out to a diffrent flex plate I could ordered the wrong Balencer.
It in the timming some were I have spark Compression Fuel.
When I advance the timing the car sems like it wants to start more offen.
Baby steps I find what causing not to run soon I hope.

 

[boomdriver]

Agree. I use a spark tester that you set the gap to match the coil output voltage you want to test. The stock L98 coil has no issue jumping the tester regardless of the gap I set. Spark is strong with a blue color. The delco coil used in L98 vettes is a high output coil.

Back in "the day"....I used to have a chart from a plug mfg that had spark colors and approx voltages listed...Blue being at the top, with red, yellow and white somewhere under that.....

That was back in the (state of the art 1970s) C.D.I. era...prehistoric HEI. (Capacitor Discharge Ignition)...damn, I'm old enough to remember points..!:ugh lol...I was 30 before I understood "dwell"...then I realized that the defination pretty well explained it..

I Looked everywhere and did the google search and can;t find that spark chart. Plenty of plug color charts for reading fuel/air but no spark color to read ignition strenght.

I can tell you that the GM HEI is a very hi voltage system and it will generate a spark somewhere if the plug is'nt able to fire. There can be arcing in the cap between rotor tip and cap, or at the contacts in plugs on/in the distributer cap. If that system generates a charge, its gonna be Discharged somewhere. When plug wires are damaged or plugs are fouled, that discharge takes place in or around the cap and will do damage to parts not designed to handle the arcing. Its hi enough voltage that it'll find a path.

PS

if YOU happen to be that path.....it hurts.

Point is,
A white spark is not hot enough to create combustion. Its harder for a spark to happen under good compression. Thats the ONLY valid reason that hi-performance motors with higher compression need a hotter ignition system. Nobody likes risking holes in piston domes from a spark thats too hot, but it has to be hot enough to jump the electrodes under hi-compression.
White is enough to make it burp but not enough to make an expolsion. A red spark may not even get a sputter.
I'd go back and inspect the module wires inside the cap, the plug in connections on the cap, and if that ign module was a replacement, you have to consider the quality if it was not delco. The module wires are famous for getting pinched under the edge of the distributer cap and creating a semi-shorted condition where some or all of the energy is grounded out before it gets to the plugs. Look for ANY breaks in the insulation of those wires inside the cap.

I have first hand experience with the "store brand" module. My motor ran but it was like it had bad gas...hesitated, rattled and performed poorly immediately after a major tune up. Someone suggested the module brand as an issue, so I got a Delco (that cost twice as much, for a reason) and the problem vanished instantly.
Knocking is simply incomplete combustion.That can come from poor spark or poor fuel/air mix. The process of combustion is fairly precise.

That spark should be so hot that you can hear it. If not, then there ain;t gonna be a fire inside.

Is it possible that the Tach and Batt wire are crossed on the cap? With individual plugs thats very easy to do.

 

[boomdriver]

Put power to the G spot the Fuel pump is working great so now I know I have a bad relay once again so I oreded one of them and a new pig tail for it.
The plugs are comming out wet so I know I getting fuel.
I going to pull the pulgs once again and put the motor back on TDC put a screw drive down the spark plug hole just to make sure TDC on the balencer mark is TDC for the compression of #1 cylinder.
I had a Trans Am many years ago that the balencer went bad and when I replaced it with a new one I now remember the timing marks were way off after that.
I remembered this last night at 2:00 AM LOL So I do the touch the pistoin trick with a screwdriver to make sure the timing marks on the New balencer are correct.
I read some where there old style balencers and new style on of the key ways on the crank sits at 12:00 at TDC and the Other is set at 2:00 position I did think about this untill last night either. The motor thats in the car now it a 1968 to 1978 I think 2 piece rear main seal driverside dipstick 4 bolt main.
I had to change out to a diffrent flex plate I could ordered the wrong Balencer.
It in the timming some were I have spark Compression Fuel.
When I advance the timing the car sems like it wants to start more offen.
Baby steps I find what causing not to run soon I hope.

Where did you find a pig-tail for the fuel relay???:confused
and how much does it sell for?

I'm needing one in a bad way. The wire on mine has shrunk back 1" or more from the plug. Got it wrapped in tape now. I've heard this is a common problem with the fuel relay and plug.

 

[vetteboy86]

Any backfiring or popping thru intake or exhaust?

 

[Marv02]

Have not looked yet But I find one.

Where did you find a pig-tail for the fuel relay???:confused
and how much does it sell for?

I'm needing one in a bad way. The wire on mine has shrunk back 1" or more from the plug. Got it wrapped in tape now. I've heard this is a common problem with the fuel relay and plug.

 

[Marv02]

So White spark is not enough I start playing witgh the gap on the plugs old dirt biker trick.

 

[boomdriver]

So White spark is not enough I start playing witgh the gap on the plugs old dirt biker trick.

White spark may have been good enough on an YZ or an Elsinore, but these modern HEI car systems are made to do REAL hi volts...Blue is the required arc. Besides, 2 strokes were LOTS less compression...no need for a hot spark. Just a clean spark for the rich oily mix.

Color indicates the voltage or strength of the spark. Remember how the new heads combustion chamber was shaped? Not round and more straight around the edge. Thats engineered with a very specific "flame path" so combustion happens under exact conditions in a very precise way. The spark strength means everything to that process. Its like trying to use a penlite flashlite to ignite a gas cloud...won;t happen, not enough heat. But, use a match and BOOM !

Spark is the same way in these engineered heads. Thats what makes a Dodge Hemi so successful, it waste no energy and can focus ALL of the combustion directly on the piston in equal amounts.Hemi heads are perfectly round and the plug sits dead center. On a Hemi you insert the plugs thru the valve cover, not the side of the cyl head like ours.
Our angled plugs ignite at an odd place over the piston, so the shape of the head has to apply and focus that explosion. That makes the spark critical.

I'm an old bike racer/builder as well, and have applied what I learned to car engines. You;d be surprised at how many people do not know about plug heat ranges and so forth.. When my engine acts up, one of the first things I do is pull plugs to read them. Thats a history as good as the ECMs memory.

If your spark is weak, that comes directly from the distributer and ignition module. widening gap makes it worse, closing the gap makes it easier but if its not Blue hot enough, its still not going to fire the motor.

 

[Marv02]

I am A CR500 AF rider my self.

And I Rode four stokes also.
KTM 560 RFS

Or was I gave it up first of the years the knees and back can not take it any more.

White spark may have been good enough on an YZ or an Elsinore, but these modern HEI car systems are made to do REAL hi volts...Blue is the required arc. Besides, 2 strokes were LOTS less compression...no need for a hot spark. Just a clean spark for the rich oily mix.

Color indicates the voltage or strength of the spark. Remember how the new heads combustion chamber was shaped? Not round and more straight around the edge. Thats engineered with a very specific "flame path" so combustion happens under exact conditions in a very precise way. The spark strength means everything to that process. Its like trying to use a penlite flashlite to ignite a gas cloud...won;t happen, not enough heat. But, use a match and BOOM !

Spark is the same way in these engineered heads. Thats what makes a Dodge Hemi so successful, it waste no energy and can focus ALL of the combustion directly on the piston in equal amounts.Hemi heads are perfectly round and the plug sits dead center. On a Hemi you insert the plugs thru the valve cover, not the side of the cyl head like ours.
Our angled plugs ignite at an odd place over the piston, so the shape of the head has to apply and focus that explosion. That makes the spark critical.

I'm an old bike racer/builder as well, and have applied what I learned to car engines. You;d be surprised at how many people do not know about plug heat ranges and so forth.. When my engine acts up, one of the first things I do is pull plugs to read them. Thats a history as good as the ECMs memory.

If your spark is weak, that comes directly from the distributer and ignition module. widening gap makes it worse, closing the gap makes it easier but if its not Blue hot enough, its still not going to fire the motor.

 

[boomdriver]

I am A CR500 AF rider my self.

And I Rode four stokes also.
KTM 560 RFS

Or was I gave it up first of the years the knees and back can not take it any more.

Nice stable !

I'm way older than either of those...lol...
I stopped before moto-x bikes got water cooling. I guess CR's had only been around 5 yrs or so when I got out of dirt and got into big street bikes. When I was 16, I got the 2nd Kawasaki Z1 903cc (fastest bike on the planet for several yrs) that came to Houston...and it only took a few months for Yoshimura to produce an 1100cc kit that I had to have. Way too much power for the suspension.

Best dirt bike I ever rode back then was a Husky 250 mag, a little hard to wrestle around a tight track but it was like a rocket on a straight piece of dirt. They've come a long long way. I wish I had been able to try a 4 stroke out....that was not even a dream in the 70's...The CR 125s were so tight on the power band that you had to keep them at 8,000 just to get it moving. Thats where I learned tons about engines....If you can build & port a 2 stroke MX bike that actually runs...you can do anything. Heck, we had a CB 450 Honda that we ported, balanced and it ran with the CB 750.
You have'nt lived until you've run a 1/4 mile on a Mach IV Kawasaki...like being launched out of a slingshot..and engine vibration that made your arms go numb...Those could do an 11 sec 1/4 but 90% of the accelleration came in about 75 ft as it hit the power band....it was so much force so suddenly that many people lost control when thier hands got yanked off the bars..

otfl we did have a 4 stroke dirt bike back then...almost forgot...Honda SL 350 2-cyl. Sort of an enduro thing that weighed 400 lbs but had the torque to actually tow another bike out of the woods...lol

 

[Marv02]

Hey here a link for the pig tail I just ordered one.

> @ Davies Corvette Parts & Accessories

Where did you find a pig-tail for the fuel relay???:confused
and how much does it sell for?

I'm needing one in a bad way. The wire on mine has shrunk back 1" or more from the plug. Got it wrapped in tape now. I've heard this is a common problem with the fuel relay and plug.

 

[boomdriver]

Hey here a link for the pig tail I just ordered one.

> @ Davies Corvette Parts & Accessories

COOL !

I see a couple that I need,

Thanks !