Weird LT1 problem

[jimmbo]

Usually this engine runs very smooth, starts within 2 seconds unless it is colder than -18, then it takes about 4 seconds. But... Some days on first start, engine occasionally would seem like it had flooded, like a stuck injector had drain the fuel line overnight. Holding the pedal to the floor would give the impression it was trying to catch. When I would let go of the key the engine would stop, then proceed to diesel backwards a few revolutions and some whitish vapour would appear from the grille where air inlet was. Two weeks ago during the cough cough cranking stage, there was a very loud back fire and a bunch of white vapour came out from all around the hood. Engine started. Took it to my cousins shop and told them I figured I had an injector that was draining the rail. Well the backfire blew the valvecover apart and pushed the gasket out. None of the plugs were fouled, but I did put new ones in. They were 8 yrs old and 80,000km(50,000 miles) and had a gap about double the .050" spec. So far it hasn't done the hard start again, nor is it missing or misfiring while running. Oil wasn't full of gas either. The engine is a Chev 2nd gen LT1

 

[MTboatguy]

My 99 Silverado was doing this at times, ended up being the Mass Air Flow Sensor had gone bad and sending the wrong signal to the brain of the truck. Mine is a 5.3 liter. The incorrect signal was throwing the timing off in the engine.

 

[gm280]

I actually had a dirty mass air flow sensor that was making the engine do all types of weird things. And even trying a general clean of the sensor, didn't work. It was not until I got a monocular (10 power) that I could actually see the dirt coating the resistive elements on the flow sensor. Then I could actually clean it. Once I cleaned all the dirt off, the engine ran like new again. I used a cut down acid brush with alcohol and gentle cleaned all the darkish coating off the little sensor resistive elements. I could see them coming clean via the 10X scope. So just looking at the mass air sensor and not seeing an accumulation of debris doesn't mean it is not dirty. JMHO

 

[robert graham]

I actually had a dirty mass air flow sensor that was making the engine do all types of weird things. And even trying a general clean of the sensor, didn't work. It was not until I got a monocular (10 power) that I could actually see the dirt coating the resistive elements on the flow sensor. Then I could actually clean it. Once I cleaned all the dirt off, the engine ran like new again. I used a cut down acid brush with alcohol and gentle cleaned all the darkish coating off the little sensor resistive elements. I could see them coming clean via the 10X scope. So just looking at the mass air sensor and not seeing an accumulation of debris doesn't mean it is not dirty. JMHO

My 1996 Roadmaster has the 350 LT-1 and it has run fine so far....I've considered removing/ inspecting/cleaning that mass air flow sensor but wonder if this is/should be preventive maintenance item or wait until some symptoms are indicated??? It looks like it would be a fairly easy job to clean it but then maybe just leave it alone????

 

[gm280]

My 1996 Roadmaster has the 350 LT-1 and it has run fine so far....I've considered removing/ inspecting/cleaning that mass air flow sensor but wonder if this is/should be preventive maintenance item or wait until some symptoms are indicated??? It looks like it would be a fairly easy job to clean it but then maybe just leave it alone????

If you do attempt to clean it, understand the little resistive elements can't take a lot of abuse. So go gentle and use a small acid brush and I used alcohol. I am sure other cleaning chemicals will work as well. But just don't brush harshly. If you can see the fine little elements, they are about a 1/4" long and about a 1/16" in diameter. At least mine were. So just remove the dirt coating because they work by changing resistive values sent to the computer. When they get coated, they don't respond correctly and that does change so many things about drivability. JMHO

 

[MTboatguy]

Those wires and sensors are so delicate, I don't even worry about cleaning them, I normally go on ebay and pick up a new one for between $30-40 bucks and run it until it dies, of course I have never had one of the ones I got on ebay go bad yet, but it is amazing how many systems that little sensor in the airflow can screw up, in my Silverado, the transmission would not shift right, the thing backfired, poor fuel mileage, buzzing noise from under the truck. Took about 2 minutes and a 10mm wrench and it purred like a kitten again.

Now on the Subaru my wife purchased back in August, I know the mechanic that did all the work on it and he had a whole list of stuff he had replaced, I mean the guy she bought it from had, had over $2400 dollars worth of work done to it and still could not get it to run right, he kept telling him that there was water in the fuel. I put my code reader on it and it threw 11 different codes. Disconnected the MAF and it would idle and run pretty good, so put a new flow sensor in it and it cleared all of the codes and purred like a kitten. Seems the mechanic I know, went to the junk yard and picked up a used flow sensor for $10 bucks and then kept putting other new parts in it trying to chase the problem down, took me 5 minutes, 10mm wrench and a $32 ebay flow sensor and have not had to do anything to is since.

The one good thing about it, she dickered down the price to way below market because they couldn't get it running right, took me $32 dollars and we have basically a car that ever single major system on has been rebuilt of replaced.

 

[gm280]

Those wires and sensors are so delicate, I don't even worry about cleaning them, I normally go on ebay and pick up a new one for between $30-40 bucks and run it until it dies, of course I have never had one of the ones I got on ebay go bad yet, but it is amazing how many systems that little sensor in the airflow can screw up, in my Silverado, the transmission would not shift right, the thing backfired, poor fuel mileage, buzzing noise from under the truck. Took about 2 minutes and a 10mm wrench and it purred like a kitten again.

Now on the Subaru my wife purchased back in August, I know the mechanic that did all the work on it and he had a whole list of stuff he had replaced, I mean the guy she bought it from had, had over $2400 dollars worth of work done to it and still could not get it to run right, he kept telling him that there was water in the fuel. I put my code reader on it and it threw 11 different codes. Disconnected the MAF and it would idle and run pretty good, so put a new flow sensor in it and it cleared all of the codes and purred like a kitten. Seems the mechanic I know, went to the junk yard and picked up a used flow sensor for $10 bucks and then kept putting other new parts in it trying to chase the problem down, took me 5 minutes, 10mm wrench and a $32 ebay flow sensor and have not had to do anything to is since.

The one good thing about it, she dickered down the price to way below market because they couldn't get it running right, took me $32 dollars and we have basically a car that ever single major system on has been rebuilt of replaced.

Yes MT, That would be the simplest and easy way to fix it. The only reason I cleaned mine was because I didn't have even one code thrown, but had a really crappy running engine that I couldn't figure out what was going on. So one by one, I removed different sensors and measured them in a real world mocked setup where I was monitoring them. And even the mass air flow sensor seemed to work pretty much correct. But I looked really close to the sensors and seen the coating on them. So I thought what the heck and thoroughly cleaned them and that fixed everything. So it wasn't like I was trying to scrimp on things, but merely working through sensors to see what was good and bad. No codes doesn't help fix things on a computer car. JMHO

 

[Scott Danforth]

Both GM and Ford had TSB's on cleaning the MAFS with electric contact cleaner back in the mid to late 90's Dust and pollen coat the hot wire sensors over time

 

[jimmbo]

Thanks for the responses. I did replace the MAFS 8 years ago and did spray clean it about a year ago. Today I managed to get it to backfire at about 4000 rpm just before shifting into second gear. Last spring it was doing that under rapid/heavy acceleration, but later quit. I'll try cleaning the sensor again. I have 3 more LT1s, one sitting in the yard for the winter, 2 more at cousins, so I can swap some parts if needed. Engine is not showing any codes.

 

[Scott Danforth]

Check timing as well

 

[jimmbo]

Check timing as well

On the LT1 there No initial setting or adjustment, totally controlled by the computers. Distributor is under water pump, against the timing chain cover(yellow in pic)

 

[Scott Danforth]

You still need to check it. Google optispark problems.... Plenty of issues with the LT1 dizzy

 

[The Bob R]

General Motors has issued a Technical Service Bulletin, indicating problems from rough idle all the way to possible transmission damage resulting from the contaminated sensors. To clean the delicate MAF sensor components, a specific MAF sensor cleaner or electronics cleaner should be used, not carburetor or brake cleaners, which can be too aggressive chemically. Instead, the liquid phase of MAF sensor cleaners and electronics cleaners is typically based on hexanes or heptanes with little to no alcohol content and use either carbon dioxide or HFC-152a as aerosol propellants. The sensors should be gently sprayed from a careful distance to avoid physically damaging them and then allowed to thoroughly dry before reinstalling. Manufacturers claim that a simple but extremely reliable test to ensure correct functionality is to tap the unit with the back of a screwdriver while the car is running, and if this causes any changes in the output frequency then the unit should be discarded and an OEM replacement installed.

 

[BigB9k]

Typical roadmaster

 

[jimmbo]

Typical roadmaster

Elaborate please

 

[BigB9k]

Oh, Sorry I wasn't serious.
Ive have been driving B-Body LT1 cars for 15 years now.
Great well built cars with a strong temperamental engine.
My 96 Caprice had the same problem when it was cold out, turned out the rear O2 wires were switched.
Before I figured it out, I solved the problem by giving it more gas and trying to keep going.

However, I never had a back-fire.

Youve gotta get that fixed, if it backfires during start up, you'll probably snap the snout off the starter.

 

[dolluper]

Those dizzy's can be probmatic but most of the time it's the coil or wire connection corrosion esp when they pop back and diesel

 

[jimmbo]

Fixed.

Bad high tension coil to distributor wire and lots of corrosion on coil terminal. Man that thing is a PITA to work on

 

[robert graham]

I checked at Autozone and they sell a brand new MAF Sensor for about $80, so if/when mine gets dirty I'll probably just buy a new one....The guy mentioned that over-oiling those aftermarket K&N air filters can cause oil-fouling of MAF Sensors.....I've always just stayed with the standard paper element air filters to avoid this potential problem....

 

[jimmbo]

K & N type filters are not so good at stopping dust either.