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Avalanche Owners Zone => Chevrolet Avalanche Problems, Questions & Answers => Problems: Engine => Topic started by: DanoWpg on December 3, 2019, 13:24:31 PM

Title: Hard Start when warm
Post by: DanoWpg on December 3, 2019, 13:24:31 PM
Hey y'all,

Long time reader, first time posting a question though. I'm getting SUPER frustrated with an issue with my 2008 LTZ with 337,000km. Several months ago, I had an initial code thrown where it was indicating that my rear O2 sensors were failing (don't remember the code off-hand). So I took it to my mechanic, who has been really good to date. They check it out and tell me they're bad and that my cats are also running way hotter than they should. He also suggests replacing the front O2 sensors as well, since they don't appear to have been replaced before (at least not since I owned the truck). So we replace the four O2 sensors, spark plugs all around (they were due to be replaced) and the two catalytic converters...a few days later, check engine light comes back but this time it's throwing a P1133 and P1153 for the front O2 sensors. They do a leak test on the exhaust and nothing found, checked the intake and no leaks, Mass Airflow sensor tests okay. Clear the codes and lets me drive it for a few days to see what happens. I drove it for a few weeks and the code comes and goes, with no rhyme or reason. I look at my cheapy scan tool and it keeps getting triggered by what it lists as TID$80 and $81 Switches Units; the min is 76 and it's going down to 65 at times, throwing the code. So I give my mechanic the info and they scan it on their tool and they can see that as well, but when they check it, it's over the minimum. Take it back home and drive it with the CEL coming on and off every few days. Then a month later, my oil pressure sensor went out and take it to my mechanic. While doing the sensor, they're going to do the intake manifold gasket and are optimistic that will fix it as they had another GM that had the same codes and replaced the intake manifold gasket and fixed it. No such luck in my case as the code is back after it went through a relearn process (their words). Back to the garage and they went through everything again, they changed the spark plugs again, saying that they seemed to be fuel fouled, but that didn't change anything.

Now here's where things get even more frustrating...they check the fuel injectors and they tell me that all the injectors are streaming out fuel instead of it being a mist and they're certain that's going to fix the two O2 codes coming up. So I tell them to change the injectors and now not only do the codes not go away, it now takes several seconds for the truck to start...but not first thing in the morning. It starts without issue first thing but if I shut it off and start it 10-15 minutes later, it cranks for several seconds before it start up and sometimes, I'll have to try it a second time before it starts. Since they did that, I ended up replacing the Mass Airflow sensor and that seems to have made the P1133 code disappear. Yesterday, they sent my truck to have the PCM reprogrammed as they found a TSB for that problem. So far, I don't have the P1153 code come up but the hard starting issue continues. I know he's going to say that the fuel pump needs to be replaced next, but it NEVER started like that until they changed the injectors and I tend to think that there's a faulty injector that's dumping fuel when it shuts down. Any suggestions would be GREATLY appreciated before going a fuel pump route.

I should mention that with my scan tool, the fuel pressure with the key on shows around 58-60psi and then when started it stays there for a bit before dropping to 43psi on average.
Title: Re: Hard Start when warm
Post by: ygmn on December 3, 2019, 13:38:27 PM
Did they check if thenew O2 sensors are any good?
Title: Re: Hard Start when warm
Post by: DanoWpg on December 3, 2019, 13:47:33 PM
Oh yeah, forgot to mention that the front O2 sensors were replaced a second time (under warranty). Both times, they were ACDelco sensors.
Title: Re: Hard Start when warm
Post by: redheadedrod on December 3, 2019, 18:15:51 PM
Generally the rear O2 sensors are just the cats... They should have just changed the cats originally and stopped there.

Have you changed the spark plugs and wires yet? Those generally can last 100k miles but can show measurable degration after 50-60k miles.

Rodney
Title: Re: Hard Start when warm
Post by: DanoWpg on December 4, 2019, 07:14:41 AM
Yeah, the wires were changed about 6 months ago and the plugs have now been changed twice in the last 6 months (last time was 2 weeks ago).
Title: Re: Hard Start when warm
Post by: EXT4ME on December 4, 2019, 08:22:16 AM
I read your fuel pressure readings.

How quickly does the fuel pressure leak down with the key off?

Perhaps check the fuel pressure with a manual gauge.
Title: Re: Hard Start when warm
Post by: ygmn on December 4, 2019, 08:54:07 AM
What are the codes stored in the engine computer?

See these sites and enter the codes for good help with issue.
Entering all the codes on some bring up specific issues like yours maybe:

https://www.obd-codes.com/
http://www.obdii.com/
https://www.engine-codes.com/
https://troubleshootmyvehicle.com/
https://www.aa1car.com/
Title: Re: Hard Start when warm
Post by: DanoWpg on December 6, 2019, 09:37:05 AM
Looks like the dealer's reprogram got rid of the P1153 code; no check engine light since it was done on Monday. I don't have a manual fuel pressure gauge, but my scan tool shows the pressure at about 5 PSI before I turn the key to the ON position (it seems to be able to read it if I turn the key to the first position) and 60 PSI when I turn the key to the ON position. The hard start is still happening if I restart the truck after 10 minutes and as late as 5 hours later. It starts normally when I first start it in the morning or it's been sitting for several hours. When the truck does finally start, you can definitely smell raw fuel from the exhaust. I suspect that it's one of the fuel injectors staying open after it's shut down and dumping fuel in the cylinder (thus losing pressure).
Title: Re: Hard Start when warm
Post by: DanoWpg on December 12, 2019, 08:14:01 AM
Still trying to figure out the hard start...last thing they did was pull the fuel rail off and checked the injectors again. No leaking from any of the injectors, so I guess that's good news. He's still baffled as to why it would start without issue when the engine is cold but hard start after sitting for 15 minutes. I have noticed this week, now that we're in a bit of a cold spell around -10F, that the that hard starting happens is less than before. What I mean is that after the initial start in the morning (which starts normally), it would hard start up to 4-6 hours in. I'm now finding with the cold temperatures outside, that's being cut down to 3-4 hours.
Title: Re: Hard Start when warm
Post by: DanoWpg on January 13, 2020, 12:38:21 PM
Still trying to figure out my issue, which is still happening. Starts normally when I start it first thing in the morning but when the truck sits for 15 minutes and longer, it hard starts. There are no codes when scanned. The truck sat unused for several days when I was out of town and it started no problem. When it hard starts I can see some black smoke and there's a definite gas smell. Any help where I should look next would be greatly appreciated. 
Title: Re: Hard Start when warm
Post by: BainMan on January 13, 2020, 12:56:15 PM
Does your fuel pump prime up on warm starts?

What is the fuel pressure:
1. idle engine running
2. key off
3. 5 minutes after shutdown
4. 10 minutes after shutdown

 
Title: Re: Hard Start when warm
Post by: DanoWpg on January 13, 2020, 13:33:55 PM
Does your fuel pump prime up on warm starts?  - Yes it does

What is the fuel pressure: Unfortunately I don't have a mechanical fuel pressure gauge, however with the scan tool I have, I can read the fuel pressure when on and about 5 minutes off.
1. idle engine running - starts at 58-60 psi and after it has warmed up will drop to 43 psi and stays there
2. key off - rises up to around 50 psi when I shut off the truck
3. 5 minutes after shutdown - around 50 psi
4. 10 minutes after shutdown - my scan tool will shut off after 5 mins
Title: Re: Hard Start when warm
Post by: BainMan on January 14, 2020, 07:03:06 AM
Can you rent/borrow/buy a mechanical fuel gauge? I suspect the fuel pump like you do, but would prefer to diagnose further before biting that bullet.
MAF and throttle body clean?
Title: Re: Hard Start when warm
Post by: ygmn on January 14, 2020, 10:21:12 AM
Egads a lot of stuff was done and it seems worse since you threw original o2 code.

do mechanical fuel pressure test at the rail.

Double check the injectors were replaced with proper ones from GM.

Title: Re: Hard Start when warm
Post by: DanoWpg on January 17, 2020, 09:17:53 AM
Can you rent/borrow/buy a mechanical fuel gauge? I suspect the fuel pump like you do, but would prefer to diagnose further before biting that bullet.
MAF and throttle body clean?

Yeah I'm going to go to the local parts store and rent a mechanical fuel gauge and get some more concrete results. The MAF was replaced last month and they cleaned the throttle body when they did the intake manifold gasket.