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Author Topic: Hard Start when warm  (Read 114 times)

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DanoWpg

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Hard Start when warm
« 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.
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ygmn

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Re: Hard Start when warm
« Reply #1 on: December 3, 2019, 13:38:27 PM »

Did they check if thenew O2 sensors are any good?
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DanoWpg

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Re: Hard Start when warm
« Reply #2 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.
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redheadedrod

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Re: Hard Start when warm
« Reply #3 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
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DanoWpg

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Re: Hard Start when warm
« Reply #4 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).
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EXT4ME

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Re: Hard Start when warm
« Reply #5 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.
« Last Edit: December 4, 2019, 08:24:59 AM by EXT4ME »
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ygmn

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Re: Hard Start when warm
« Reply #6 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/
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DanoWpg

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Re: Hard Start when warm
« Reply #7 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).
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