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04-14-2019, 11:53 AM | #1 |
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Join Date: Dec 2017
Location: Mile High
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Stumbling on Cold Starts
Gents,
I have an LQ4/4L80e that I am finishing up. Brendan @ lt1swap programmed the ecm for me. The first few times (first couple of weeks) I cranked and ran the engine, no issues. The last three times I've cranked the truck on a cold start, it stumbles heavily and didn't start first time two of those attempts. After the first time it did it, the next day, I cycled the key a couple of times to make sure the fuel was not bleeding pressure down. That did not help. After the truck starts and runs for a minute, all subsequent attempts to start are fine. I have not road tested the setup yet. All attempts are in the garage. Any thoughts? |
04-14-2019, 01:37 PM | #2 |
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Location: Pasco, wa
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Re: Stumbling on Cold Starts
Have you replaced the intake manifold gaskets? Stock ones start to crumble after this amount of time and create a big vacuum leak until the engine runs for a minute or two. Runs like it has a misfire and will throw codes for mass air flow sensor performance.
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1972 C10 cheyenne super -350/th350 Wifes truck 1971 Nova- 6.0l with some goodies and a t56, 98-02 camaro brakes all around, tubular control arms, etc 2000 zr2 blazer- rock crawler offroad toy, one ton axles and lockers front and rear. 2006 2500hd- 500hp duramax/built allison trans,traction bars, and some other goodies. |
04-14-2019, 01:47 PM | #3 | |
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Re: Stumbling on Cold Starts
Quote:
No codes yet. That also makes it weird for me. The only code I have ever gotten was when I forgot to plug the peddle in once. |
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04-14-2019, 01:52 PM | #4 |
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Re: Stumbling on Cold Starts
Replace the knock sensors and harness while your in there
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1972 C10 cheyenne super -350/th350 Wifes truck 1971 Nova- 6.0l with some goodies and a t56, 98-02 camaro brakes all around, tubular control arms, etc 2000 zr2 blazer- rock crawler offroad toy, one ton axles and lockers front and rear. 2006 2500hd- 500hp duramax/built allison trans,traction bars, and some other goodies. |
04-14-2019, 02:12 PM | #5 |
meowMEOWmeowMEOW
Join Date: Sep 2009
Location: MKE WI
Posts: 7,128
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Re: Stumbling on Cold Starts
Were the attempts all in similar temps? (and is the motor mostly stock?)
Hot and Cold starts are affected by ASE or After Start Enrichment. On a somewhat modded motor, these values may need to be tweaked to prevent stumbling. If the temps drop and the air density spikes, the factory ASE on a modded motor doesn't keep up.
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'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD
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04-14-2019, 10:25 PM | #6 | |
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Re: Stumbling on Cold Starts
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04-15-2019, 05:50 AM | #7 |
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Join Date: Jun 2015
Location: Atlanta, GA.
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Re: Stumbling on Cold Starts
I had a similar problem recently and found out it was a bad O2 sensor. Here is my thread.
http://67-72chevytrucks.com/vboard/s...ight=stumbling Gets interesting around page 3.
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Jay Gesner Atlanta, GA 1985 C10 Long Bed 4X2 LS 5.3, 4L60E Father/Daughter Project |
04-15-2019, 01:47 PM | #8 | |
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Re: Stumbling on Cold Starts
Quote:
Since I have a 100K plus motor, I'll start here and replace the O2 sensors with new ones. I'll follow-up tonight and after the O2 swap. |
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04-16-2019, 08:41 PM | #9 |
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Re: Stumbling on Cold Starts
Quick update. Had my first cold start tonight. it had a very slight stumble before firing off. And, interestingly enough had a CEL. P0135 code, O2 sensor. So, I'm going to replace both O2 sensors like Wgesnerjr suggested and will report back in the next couple of days.
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04-16-2019, 09:58 PM | #10 |
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Re: Stumbling on Cold Starts
P0135 is a 02 heater circuit, could be heater element in the sensor or a ground issue. I cant remember what years silverados and other fullsize trucks/suvs it was but they had a common problem with a bad ground causing that code. The 02 sensor body grounded through the exhaust pipe itself, quick test was to command the heater on with a tech2 and if it didnt work take a piece of wire strip an inch or so bare and wrap it around the sensor body then put the other end on a good clean ground and try it again.
Engine doesnt run off of the o2 sensors until it hits a set temperature, cold starts are all off of the "base" tune aka open loop. Easy check for intake gaskets leaking is grab a can of carb clean, brake clean, etc and spray down both sides of the intake where it meets the cylinder head BEFORE you start it the first time for a cold start. Spray it down real good then run around and fire it up real quick, if it idles higher than normal that confirms it. You can also smell the brake clean/carb clean in the exhaust if you put enough down.
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1972 C10 cheyenne super -350/th350 Wifes truck 1971 Nova- 6.0l with some goodies and a t56, 98-02 camaro brakes all around, tubular control arms, etc 2000 zr2 blazer- rock crawler offroad toy, one ton axles and lockers front and rear. 2006 2500hd- 500hp duramax/built allison trans,traction bars, and some other goodies. Last edited by rennat_2006; 04-16-2019 at 10:07 PM. |
04-16-2019, 10:15 PM | #11 | |
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Re: Stumbling on Cold Starts
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04-17-2019, 06:17 AM | #12 |
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Re: Stumbling on Cold Starts
I understand the ECU doesn't adjust Air Fuel Ratio until warm. However, in my case, the O2s DID have some kind of affect on start up. I think it's has to do with After Start Enrichment ASE, (thanks Br3w City) which is what old school guys would call a choke.
From the limited info I found, ASE is a table that is used to get the engine started and up to temp then the ECU would take over Air Fuel Ratio. Again, not much info out there. So I think ASE uses the heater in the O2 to heat up the sensor so the ECU can run the ASE table. My stumble was only for first 45 to 90 seconds or so. But the O2 heater did not work on my sensor and caused a rich mixture on that side of the engine. Here is the test I used for the heater check. https://www.motor.com/magazine-summa...cuit-failures/ Also, in my case the sensor that caused my stumble was a Denso sensor installed during engine swap. But I think the exhaust shop I used may have welded the O2 bungs in with the sensor in place, there by damaging the heater part. I replaced with ACDelco and immediately cleared up problem.
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Jay Gesner Atlanta, GA 1985 C10 Long Bed 4X2 LS 5.3, 4L60E Father/Daughter Project |
04-20-2019, 12:34 AM | #13 | |
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Re: Stumbling on Cold Starts
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04-20-2019, 12:33 AM | #14 | |
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Re: Stumbling on Cold Starts
Quote:
I sprayed a ton of carb cleaner on the top sides of the manifold gaskets and then jump in and cranked it. No high rev or high idle. However, I should mention that it did not stumble either. I moved forward with replacing the O2 sensors and will post a message of the stumbling comes back. |
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04-20-2019, 06:01 PM | #15 |
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Re: Stumbling on Cold Starts
I had a similar issue a year after I had my truck running with no issues. Gave it some thought... stumble at startup = no fuel in lines. I checked my gas tank vent line and it dropped down from where I had originally placed it. Realized it was level or just below level and with the fuel sloshing around it had some fuel in the line that was causing a vacuum / clog. Cleared it out, moved the line back up and resolved the startup stutter, make sure your vent is clear.
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04-20-2019, 07:05 PM | #16 | |
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Re: Stumbling on Cold Starts
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06-26-2019, 09:19 PM | #17 |
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Re: Stumbling on Cold Starts
Sorry for bringing up such an old thread. But after 2 months, I have had no problems since replacing the O2 sensors. I know there are certain folks that swear the O2 sensors do not cause these types of issues. But, I am not having any more issues!
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