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Could it be a fuel pressure bleed off issue. If injectors don’t have proper pressure on the first impulse the delivery could be insufficient (lean) and this could cause a knock initially. No?
Check fuel pump/cycling/pressure release.

The heat is bringing the issue forward; it is not the root cause.
 

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I don't know if that shows as much as the GM computer interface. I have a chinese Tech2 that I use on my other GM vehicles and the functionality has been great for diagnosing and repairing my cars and my friends. I paid $280 while the GM ones were $2k+. It works just like the Tech2 the dealer had back when I was working there.

It would seem that data logging what is going on when this happens might give some information to help narrow this down. I know you shouldn't have to, but, it might go a long way in getting the problem resolved.
GDS not TECH2
 

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Discussion Starter #143
Just my theory------I believe the fuel pressure is dropping off due to the leakage from injectors, then with the fuel & pressure absent it struggles to start until fuel/pressure is back to normal(struggling gets worse the more injectors that leak....the excess fuel that drained into the combustion chamber is igniting during starting, causing the valve clatter(bigger explosion than usual)...what is causing the leakage is the big question. the outside shop said my fuel pressure was losing 8 psi over the course of an hour due to the 6 leaky injectors. I may be way off base.. but again..just my opinion.
 

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Just my theory------I believe the fuel pressure is dropping off due to the leakage from injectors, then with the fuel & pressure absent it struggles to start until fuel/pressure is back to normal(struggling gets worse the more injectors that leak....the excess fuel that drained into the combustion chamber is igniting during starting, causing the valve clatter(bigger explosion than usual)...what is causing the leakage is the big question. the outside shop said my fuel pressure was losing 8 psi over the course of an hour due to the 6 leaky injectors. I may be way off base.. but again..just my opinion.
Let's just run with your theory for a moment then. If what you say were true, you should be able to pull practically any plug and find things wet. Also, if you were to try to start the car with the gas pedal to the floor forcing the injectors to stay shutoff, then you'd think the car would at least "pop" trying to start. With the gas pedal to the floor, the injectors should be shut off but I don't think it kills the spark. And if there was fuel leaking from the injectors, why would that problem cure itself after 2 hours?

I don't know if the SS is like the '14 plus Silverados, but after the vehicle sits for a time with the fuel pressure dropped, the moment you open the driver's door you can hear the fuel pump bring the system up to pressure. If the SS acts the same way, then there would be no waiting for fuel to get to the cylinders on startup.

We keep getting wrapped around the pole thinking this problem is fuel related, but I'm thinking the reason for the sputtering start is due to timing. Given the time frame when the problem "struggling starts" happen, (roughly 15-20 minutes after engine stop) it seems to point to a heat issue. The ECM tells this thing when to spark based on a number of sensors, the ECT, M.A.P., Knock, MAF, Crankshaft position, camshaft position, there are probably more. (I talked with my tech friend about this and he said take a good look at the MAF sensor and make sure those sensing wires are clean. A little bug in the right spot on a MAF will make an engine do the goofiest things.)

One question I haven't heard asked or answered is do you know went this problem started? Has it done this since new? To @Kevin Smith - it shows you owning the car starting at 3000 miles, are you sure nothing has been done to it prior to you getting it? Getting this car with that number of miles makes me wonder if it was a salesman's program car or if someone else had it for a time, fiddled with it, then dumped it.

I would love to hear a happy ending to this puzzle, but until more data comes in, all we can do is keep guessing.
 

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Discussion Starter #145
Let's just run with your theory for a moment then. If what you say were true, you should be able to pull practically any plug and find things wet. Also, if you were to try to start the car with the gas pedal to the floor forcing the injectors to stay shutoff, then you'd think the car would at least "pop" trying to start. With the gas pedal to the floor, the injectors should be shut off but I don't think it kills the spark. And if there was fuel leaking from the injectors, why would that problem cure itself after 2 hours?

I don't know if the SS is like the '14 plus Silverados, but after the vehicle sits for a time with the fuel pressure dropped, the moment you open the driver's door you can hear the fuel pump bring the system up to pressure. If the SS acts the same way, then there would be no waiting for fuel to get to the cylinders on startup.

We keep getting wrapped around the pole thinking this problem is fuel related, but I'm thinking the reason for the sputtering start is due to timing. Given the time frame when the problem "struggling starts" happen, (roughly 15-20 minutes after engine stop) it seems to point to a heat issue. The ECM tells this thing when to spark based on a number of sensors, the ECT, M.A.P., Knock, MAF, Crankshaft position, camshaft position, there are probably more. (I talked with my tech friend about this and he said take a good look at the MAF sensor and make sure those sensing wires are clean. A little bug in the right spot on a MAF will make an engine do the goofiest things.)

One question I haven't heard asked or answered is do you know went this problem started? Has it done this since new? To @Kevin Smith - it shows you owning the car starting at 3000 miles, are you sure nothing has been done to it prior to you getting it? Getting this car with that number of miles makes me wonder if it was a salesman's program car or if someone else had it for a time, fiddled with it, then dumped it.

I would love to hear a happy ending to this puzzle, but until more data comes in, all we can do is keep guessing.
Question:

Do I hold the brake and gas pedal to the floor while trying to start for 5 seconds?? or just the gas pedal and and press start? because when I did the gas and brake pedal to the floor yesterday after a 15 minute wait after a 5 mile drive..when I tried to start the car..it almost redlined before I let off the gas! Scared the crap out of some people in the grocery store parking lot i must say.

and to answer your other question...the issue started about 3 months after I purchased the car. never did it when i first got it. I even asked the finance manager if he had the issue..he said no.
 

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It seems to me the moise is definitely a lean engine knock from the recording thats what it sounds like... has anyone thought of the intake leaking possibly... that could cause this issue and also change with temp issues.... This is where I would start after reading all this stuff.... Something along the lines of this...
 

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Question:

Do I hold the brake and gas pedal to the floor while trying to start for 5 seconds?? or just the gas pedal and and press start? because when I did the gas and brake pedal to the floor yesterday after a 15 minute wait after a 5 mile drive..when I tried to start the car..it almost redlined before I let off the gas! Scared the crap out of some people in the grocery store parking lot i must say.

and to answer your other question...the issue started about 3 months after I purchased the car. never did it when i first got it. I even asked the finance manager if he had the issue..he said no.
This is great information!

First, your foot has to be on the brake in order to get the engine to even turn over when you push the start button.
If your foot had the gas pedal to the floor at the same time, the engine should NOT have started due to the injectors being shut off. If that is what you are saying happened, that brings a new twist to the situation. (Your sure you had the gas pedal all the way down?)

Now I'm wondering if this is something other than a sensor...... BCM?? ECM???
 

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Discussion Starter #148
This is great information!

First, your foot has to be on the brake in order to get the engine to even turn over when you push the start button.
If your foot had the gas pedal to the floor at the same time, the engine should NOT have started due to the injectors being shut off. If that is what you are saying happened, that brings a new twist to the situation. (Your sure you had the gas pedal all the way down?)

Now I'm wondering if this is something other than a sensor...... BCM?? ECM???
I am pretty sure it was all the way down....when I pressed the start button it struggled for maybe a half second and then WHAMO it started and went to high revs...that is when I immediately took my foot off the gas...
 

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I am pretty sure it was all the way down....when I pressed the start button it struggled for maybe a half second and then WHAMO it started and went to high revs...that is when I immediately took my foot off the gas...
After thinking about this a bit more with given what you said, maybe you've got a flaky Throttle Position Sensor.

I just went out and tested my SS by holding the gas pedal to the floor, foot on the brake, hit the start button and it cranked for 5 or more seconds till I hit the start button again to stop it. I then took my foot off the gas pedal, kept the other foot on the brake, hit the start button and it started normally. No runaway revs at all. I even went so far as to see where the rev limiter would kick in - it would not let the engine go past 4,000 rpms.

So my question for you is, do you believe or did you notice how high your rpm's shot up to when you attempted to start the engine with your gas pedal firmly planted to the floor? Are you sure it went well above 4,000 rpms?
 

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Discussion Starter #150
After thinking about this a bit more with given what you said, maybe you've got a flaky Throttle Position Sensor.

I just went out and tested my SS by holding the gas pedal to the floor, foot on the brake, hit the start button and it cranked for 5 or more seconds till I hit the start button again to stop it. I then took my foot off the gas pedal, kept the other foot on the brake, hit the start button and it started normally. No runaway revs at all. I even went so far as to see where the rev limiter would kick in - it would not let the engine go past 4,000 rpms.

So my question for you is, do you believe or did you notice how high your rpm's shot up to when you attempted to start the engine with your gas pedal firmly planted to the floor? Are you sure it went well above 4,000 rpms?

I did not look at the RPM's when I did it. Was watching the people behind me scamper with their shopping carts...(wasn't expecting it to start.) So I don't know how high they went. I will try again and repost either tomorrow or Monday.

I do want to say thank you to all that have provided ideas/suggestions for this issue....I hope one day we can dial it in! :)
 

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Just tried that on a cold engine, you auto guys have it easy for that procedure lol. Nothing unusual on a cold start the next time I drive it I will try it on a hot start.

I am glad this issue is getting some attention one way or another it's pretty embarrassing when you start the car and it sounds like it is going to die in public.
 

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This is great information!

First, your foot has to be on the brake in order to get the engine to even turn over when you push the start button.
If your foot had the gas pedal to the floor at the same time, the engine should NOT have started due to the injectors being shut off. If that is what you are saying happened, that brings a new twist to the situation. (Your sure you had the gas pedal all the way down?)

Now I'm wondering if this is something other than a sensor...... BCM?? ECM???
Well I just did a thing on a nice hot engine and it didn't behave like it did when the engine is cold. It sputtered and immediately started and red lined.......

So what does that mean, btw I tried this after letting the car sit for about 10 minutes while I ran into the store and it clicked like it did when it was cold this confirms something is getting hot and needs at least 20-30 minutes for it to not be happy.
 

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Discussion Starter #155
This is great information!

First, your foot has to be on the brake in order to get the engine to even turn over when you push the start button.
If your foot had the gas pedal to the floor at the same time, the engine should NOT have started due to the injectors being shut off. If that is what you are saying happened, that brings a new twist to the situation. (Your sure you had the gas pedal all the way down?)

Now I'm wondering if this is something other than a sensor...... BCM?? ECM???
Well I just did a thing on a nice hot engine and it didn't behave like it did when the engine is cold. It sputtered and immediately started and red lined.......

So what does that mean, btw I tried this after letting the car sit for about 10 minutes while I ran into the store and it clicked like it did when it was cold this confirms something is getting hot and needs at least 20-30 minutes for it to not be happy.
anyone seen this story? https://www.caradvice.com.au/768453/holden-commodore-ls3-v8-fuel-injector-dramas/
 

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I am still calling BS on the fuel unless Australia and the US are getting bad fuel in random isolated spots on a daily basis so lets put that argument to bed.

I still find it hard to believe you have chewed through three sets of injectors without anything else causing the issue. Did they change the injectors on the 16 and 17 engines, why did they only reference those two years in the article?
 

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Discussion Starter #157
I am still calling BS on the fuel unless Australia and the US are getting bad fuel in random isolated spots on a daily basis so lets put that argument to bed.

I still find it hard to believe you have chewed through three sets of injectors without anything else causing the issue. Did they change the injectors on the 16 and 17 engines, why did they only reference those two years in the article?
I don't think it's fuel quality either...we have Bosch injectors...I asked if I could get another brand installed last time..Chevy said no.
 

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I doubt it's injectors at all. Unless a something cooks them but that would not result in a hot start issue.What's the procedure after installing injectors? A learn or reset? I would lean toward a sensor that isn't throwing a code but changes with temp. Like a crank sensor of old days. They failed intermittently and would change the pickup signal with heat. If a dealer was on it they would do more diagnostics and maybe even get an ecu to swap out. The fact that it is repeated in other cars means there is more than likely a defective electrical component scrambling the brain or the brain itself. Temporary insanity.
I tried to quick read the history here but never saw any data collected that compared a good start bad start. Before the dealers get forced to buy the lemons back, swapping out the brain box would seem like a... no brainer! A sticking lifter just would not be that consistent but possible with temperature change cooling differential causing an exagerated clearance issue. Clatter, misses...thats the only mechanical condition that could likely cause the symptoms. The same kind of temp change can cause defective electrical parts to expand or expose a crack in a board circuit.
Keep up the pressure, demand a loaner and get GM to do their homework. Everybody loves a good mystery story solved. Legal paperwork generallly gets results.
 

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Interesting story for sure..... but the issue you've been having doesn't fit this problem. Has your car experienced a performance loss or gone into "limp mode". You haven't mentioned any problems once the car starts running. Have you had any??

Wait now, if you are on your 3rd set of injectors, these things can't be failing at that fast a rate. Didn't you say you only have 11,000 on the car?
 
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