Cold start hesitation

[dwinters14]

I believe I've figured out my issue but I wanted to get a second opinion and also create a thread for future reference for others with the same issue.

Vehicle:
2007 Suburban LT, 5.3L, 2WD Flex Fuel

Problem:
Delayed start when cold. Truck always starts, and idles afterwards, and will fire first crank the second time.

*** Most probable cause E85 ***

Troubleshooting:

Firstly, NO CODES. I exclusively fuel my truck with E85 for the cost savings and also the drivability compared to regular octane fuel. In my live data the truck read 69% alcohol content. In the past two years I've replaced the following items associated with starting. Battery, alternator, purge valve on engine, vent valve by fuel tank and fuel pump. I haven't changed anything else. The first thing I did to narrow down the issue is check cold cranking voltage on the battery which has been a steady 12.2v to 12.8v. Starter fires every time. I recently replaced both the purge valve on the engine and verified it's working properly as well as the vent valve by the fuel tank and also verified it's working properly.

The next test was to check out the fuel pump/check valve assembly. I threw a gauge on the fuel rail and here were my numbers:

Dry: 0 PSI
Key in, on position: 50 PSI
Started and idling: 58 PSI steady
Off: 51 PSI
10 Minutes off: 49 PSI
1 Hour off: 25 PSI

From here the only other thing I can extrapolate besides fuel is something deeper, timing, cam position sensor, ECM issue with the alcohol content or a multitude of other gremlins. Once on, the truck holds and idles very well and has power throughout the entire powerband through every gear. The engine fires every time when warm as well.

I did do some research on E85 and it seems problematic when igniting on a cold engine. This issue has come and gone since I've owned it, but I never knew where to point the finger as all the other parts listed above were bad. Now that I've narrowed them out I'm looking at what's left. The easiest way to confirm or deny my concerns is to run the tank dry and put regular octane fuel in it and see, or combine it with the ethanol already in the tank to see if it helps ignite better.

Before I get to that stage, does anyone have any other potential ideas? I like to explore all avenues as I have frequently found really odd things can disguise themselves in their symptoms.

 

[Fless]

Unless I'm reading this wrong, you don't have a delayed crank; you have delayed start.

Harder starting in cold temps can be an issue with E-85. Many stations will reduce the alcohol percentage during cold weather for this particular issue. One thing you can do is reduce the amount of E-85 by mixing it with (more) gas.

Also note that GM issued some updated calibrations for some GMT-900 engine computers to be able to properly calculate the alcohol percentage, since they don't have physical sensors. Might want to make sure yours has the update if it's available for your truck.

My '04 has a physical sensor and I typically run E-70 all the time. No trouble with hard starts, even in the cold. YMMV

 

[dwinters14]

Unless I'm reading this wrong, you don't have a delayed crank; you have delayed start.

Harder starting in cold temps can be an issue with E-85. Many stations will reduce the alcohol percentage during cold weather for this particular issue. One thing you can do is reduce the amount of E-85 by mixing it with (more) gas.

Also note that GM issued some updated calibrations for some GMT-900 engine computers to be able to properly calculate the alcohol percentage, since they don't have physical sensors. Might want to make sure yours has the update if it's available for your truck.

My '04 has a physical sensor and I typically run E-70 all the time. No trouble with hard starts, even in the cold. YMMV

Yes you are correct, I will edit my original post. I have heard about the ECM reading the alcohol % incorrectly resulting in drivability issues. Let me do a little research and see what's available for the GMT900.

 

[jcbarbour72]

I had a similar issue, though I don't use E85. I could sit and crank on it for a bit and it would eventually fire up. I determined it was just not getting enough fuel initially. After some research, I replaced the Ignition Fuel Pressure Regulator. I was slowly leaking pressure there and it needed to build up before enough properly fueling the engine.

Here is the part I used on my 2001 Yukon XL Denali 6.0 for reference. Yours should be similar:

 

[dwinters14]

Just wanted to bump this to potentially get some more info as to the cause of the issue. Since I've posted this I had a crack in my PCV which caused a lean code, as well as a P0420/P0430. I started noticing a hesitation while driving and even almost stalled. I thought it might be my torque converter since my idle was low but with some research I decided to do some other things first.

For peace of mind I did wires/plugs. They were both original and the plugs were NGK's which I simply replaced with the same. I also cleaned my throttle body which was obviously covered in carbon and oil, put the new valve cover on with the updated baffle and an oil catch can fixing the crack hose. I also cleaned my MAF which suspiciously improved my idle and driving performance as well as cleared my P0420/430 codes. I drove it like this for about a week before I determined it was simply slowing dying, so I replaced it and the vehicle has been driving better since.

Now I'm still having the cold start issue and the crank is twice as long and almost stalls. I still run E85 because 87+ octane is almost $5/gal and I can't afford that these days. I want to check my injectors and see if there's a leak but I also did a couple of other tests when diagnosing my P0171 code and they were watching my 02's voltage, and both primary 02's stayed between the 0.0 to 1.0 V range and my fuel trims were proper (I don't remember right now, but I think my short term were under 5% variance and my long terms were 0%-1%) which ruled out a rich or lean condition.

Does anyone have any ideas as to what else I can check to see what's going on? The truck has to sit for at least 6+ hours before it'll slow crank, and it'll only ever do it once when cold. Otherwise it'll fire right up even if I cut the engine right away.

 

[j91z28d1]

again, just to be clear, slow crank doesn't meant your starter is slowly turning the engine over? if it sounds good and spins fast but just cranks a long time before starting. that is definitely different, even thou I have had a battery that load tested weak and cranked slowly start up badly too. stated way sooner and cleaner with a fresh battery and stater.

but anyways if it's a long crank time first thing in the morning, cold engine, not cold air temp. cold air temp in the 30s with e85, just be lucky it started at all haha. so cold engine but 70s or so outside air temp. long crank time at first startup. as a trick, try clicking the key on and pause there for a second or so and then go to start. that little pause let's the fuel pump build pressure before you get the motor spinning and ecm starts the startup fuel routine. that routine is adjusted based on full fuel pressure, if you have injectors bleed down or fuel pump check valve bleed and start cranking before the pump can bring pressure up. I've seen it long crank and then run rough for a second till it cleared out. it will trick you into it removing crank fuel from the tune, but its not right.

just something free and easy to try. if it doesn't work, and it bothers you enough. e85 is ****** on injectors. pull them and ship them off to be cleaned and flow tested. always oem fuel pumps seem to hold fuel pressure better then auto parts store ones, if you think yours has been changed with a cheap one.

oh and maybe reset your alcohol % in the ecm. even if you're running e85 and it's drifted to far away from actual content the a/f can be off enough it might not start great.

 

[dwinters14]

again, just to be clear, slow crank doesn't meant your starter is slowly turning the engine over? if it sounds good and spins fast but just cranks a long time before starting. that is definitely different, even thou I have had a battery that load tested weak and cranked slowly start up badly too. stated way sooner and cleaner with a fresh battery and stater.

but anyways if it's a long crank time first thing in the morning, cold engine, not cold air temp. cold air temp in the 30s with e85, just be lucky it started at all haha. so cold engine but 70s or so outside air temp. long crank time at first startup. as a trick, try clicking the key on and pause there for a second or so and then go to start. that little pause let's the fuel pump build pressure before you get the motor spinning and ecm starts the startup fuel routine. that routine is adjusted based on full fuel pressure, if you have injectors bleed down or fuel pump check valve bleed and start cranking before the pump can bring pressure up. I've seen it long crank and then run rough for a second till it cleared out. it will trick you into it removing crank fuel from the tune, but its not right.

just something free and easy to try. if it doesn't work, and it bothers you enough. e85 is ****** on injectors. pull them and ship them off to be cleaned and flow tested. always oem fuel pumps seem to hold fuel pressure better then auto parts store ones, if you think yours has been changed with a cheap one.

oh and maybe reset your alcohol % in the ecm. even if you're running e85 and it's drifted to far away from actual content the a/f can be off enough it might not start great.

Yes to clarify it's turning over, but not firing so the starter is doing it's job properly. Engine cold but outside temp these days is 85+ so not actually cold. When I was doing all my diagnostic work my scanner saw 69% alcohol content, I'm not sure what E85 actually is at the pump.

I will cycle the key on and let it sit until all the "dings" are done and try to start it and see if it changes anything tomorrow. I have done it recently, but I don't recall it being much better, maybe a millisecond less crank time. Sometimes it'll run rough for about one or two seconds but once she's on she runs fine.

I think my pump is delphi flex fuel, I had to have a shop replace it about 2 years ago now and I remember us talking about it.

How can I reset the alcohol content? I don't have a GM scanner.

 

[j91z28d1]

I don't know what level scanner it takes to reset the %. I do believe a clone tech 2 will do it. but I'd think others could. scanners just seem to be hit or miss at that options they have and it's hard to say without using it on your specific truck. like my tech2 doesn't show it on mine since I'm guessing it's not flex fuel rated.


shouldn't take note than a half second of a pause in my experience. Just click on, pause and cranks. wait to long and the pump times out.


byond that, if you can't reset and test on a tank of gas. maybe someone like black bear tune could adjust the maps a bit for you? hard to say without asking them.

 

[dwinters14]

I don't know what level scanner it takes to reset the %. I do believe a clone tech 2 will do it. but I'd think others could. scanners just seem to be hit or miss at that options they have and it's hard to say without using it on your specific truck. like my tech2 doesn't show it on mine since I'm guessing it's not flex fuel rated.


shouldn't take note than a half second of a pause in my experience. Just click on, pause and cranks. wait to long and the pump times out.


byond that, if you can't reset and test on a tank of gas. maybe someone like black bear tune could adjust the maps a bit for you? hard to say without asking them.

No change in the long crank this morning. I did find out my exhaust manifold is leaking making a loud tick but that's it.

 

[j91z28d1]

No change in the long crank this morning. I did find out my exhaust manifold is leaking making a loud tick but that's it.

oh well, with a try. in theory the leak also sucks in air and can make your o2 sensors read lean. so your long term trims adjust to richer than it actually is. I don't know that it would bother start up. but I did the external clamp on mine, it has worked well so far.