5.3 Rough Cold Start

[jason78]

I have a 5.3L in my 2005 Suburban with 180K miles on it. Having an issue where on cold starts, (if it sits a couple days but normal 80 degree or so outside temp) when you start it, it starts right up but starts very rough. It kind of shudders a bit and sometimes causes the belts to squeal. It's just for an instant then idles out smooth and she's good to go after that. Warm starts are great, starts right up smooth. No check engine light.

I was also having a problem with hard starting as in it turned over for 5-6 seconds before starting randomly. That problem was resolved by replacing the fuel pump/regulator assembly in the tank. This rough cold start condition existed before and still exists.

Any ideas are greatly appreciated. Thanks!

 

[#1taho]

Check and see if you have a fuel pressure regulator. But there is a few things it could be. See if your mass air flow sensor is clean also

 

[jason78]

Thanks for the reply! I already changed out the fuel pressure regulator. On my year, it's built in to the fuel pump assembly. That resolved part of my problem but the cold rough start problem remains. I was thinking about the MAF sensor too. I wonder if I unplugged it and let the ECM use default values then tried to cold start. Maybe that would tell me if its the MAF?

 

[jason78]

Just wanted to circle around and say that replacing the Mass Airflow Sensor solved the problem. I unplugged it and started smooth. Replaced with OEM Delphi MAF AF10043 from Rock Auto for about $80. May have been able to clean it but it did not look all that dirty and I figured I may as well replace after 11 years and 180K miles.

Not only did this resolve the cold starting issue, it also seems to have solved an issue with the Burb feeling a bit sluggish, like I could not push the gas pedal all the way down (but I could). Anyway that seems like it was the fix. Wanted to update the thread. Drives me crazy when people leave threads open without final update. Thanks for the comments.

 

[retiredsparky]

Thanks for the update. The info helps the rest of us have an idea what to check. The coolant temp sensor and intake air sensor have an impact at start up as well. During the starting sequence the PCM bypasses the O2 sensors, due to low exhaust temps on start-up. Did you have codes/check engine light?

 

[jason78]

I did not check for codes but did not have any CEL light events so I did not think I would find any codes. I did of course have CEL after I started the engine with the MAF disconnected. ECT sensor was the next thing I was planning to change. The temp gauge seems to be accurate and assuming there is only one ECT reporting to the PCM so decided to try MAF first, especially since the problem disappeared after I unplugged the MAF.

 

[jason78]

Well hate to say that it seems like I am close to being back at Square 1 with my issue. Suburban sat a week and when I cranked it up I got the same thing but did not seem quite as bad. Any other ideas on what to change out next? Again, it cranks right up but if it sits for an extended period, it has a surge and instant of not running well. Sounds like an unhealthy start but them idles out fine. If its driven daily it does not have the issue. Strangely, its only if it sits for several days. Changing the MAF sensor may have helped and definitely improved performance on the road so don't regret changing that. Wondering about MAP and ECT sensor, maybe Crank Position Sensor as well. Seems like there are several sensors involved. Ideas welcome.

When I unplugged the MAF, would the PCM have defaulted any other sensor values as well? That may be the key since it did not do this when I had the MAF unplugged and gave it a cold start. If it defaulted another sensor along with the MAF, that may be the sensor.

 

[ISU-152]

I'd go back to fuel pressure. Are you in the habit of just jumping in and cranking or do you turn the key to on and let the fuel pump run first?

 

[ISU-152]

Did you ever pull the negative battery cable after maf replacement?

 

[jason78]

Normally I just crank it right over. I have several other GM 5.3 vehicles of this vintage and it has never been an issue. Around the time all this started, I also had an intermittent issue where it would sometimes have to turn over for 6-8 seconds before cranking. Once that started, I did do the ignition ON delay to let fuel pressure build up as a work around. I then changed the fuel pump/pressure regulator in the tank. That resolved the cranking issue however the rough start after its been sitting remained. I did not unplug the Negative battery cable after replacing the MAF. I have driven about a thousand miles since I replaced it. Do you think there is any use in doing that? This seems to be a minor issue, I'm just picky about things running right and it bothers me. Thanks!