2001 5.3L Suburban - hard or no start when below zero degrees

[mike_2001]

Hello. I have have had this vehicle for 5 years. Since I have had it, it has given me troubles starting below zero degrees fahrenheit. Soon after I bought it, it failed to start at minus 20 degrees, with the block heater plugged in (cranked nice, but no start). Since that time, it has seemed to degrade slightly, giving me troubles starting even at about minus 5 degrees. These are "first thing in the morning" starts that give trouble. If the engine was warm from previous running, it starts fine. Starting it at above zero temps "first thing in the morning" is just fine.

 

I replaced a fuel pump in 2010, and now just about one month ago, I installed a Delco fuel pump. It gave me trouble starting this morning, at about minus 5 degrees. I checked the fuel pressure after the first failed start attempt, and it was about 58 psi, key on, engine off. It held pretty good too. When cranking, I believe it was around 55 psi. It did eventually start, after about 4 or 5 attempts, and then ran fine every time later today when started.

 

What could this be? It doesn't seem to have any running problems, other than piston slap at startup, and oil consumption of about 1 quart per 2500 miles or so.

[Doug_Scott]

Always start with the basics. There are three things required for an engine to start. Fuel, spark and compression(some say "air", but, no air means no compression).

 

When was the last time you looked at spark plugs and other parts of the ignition system? You may want to take a look at what the battery voltage is when cranking. It must be high enough to support ignition and fuel systems, while cranking.

 

About the only thing that is variable on a cold engine is the air temp sensor reading. If it is reporting the air temp as being above zero, the computer will not inject enough fuel for the engine to run properly. Think of it like a choke on a carburetor. If the choke is open on a cold start, it is very difficult for the engine to start, let alone run at below zero temps;

[mike_2001]

Thanks for the reply. Plugs haven't been changed, and are probably due. Are there other aspects of ignition likely?

 

As to the air temp sensor, where is that located? I imagine I could check the reported temp through the obd2 output, to see if accurate.

[Doug_Scott]

Thanks for the reply. Plugs haven't been changed, and are probably due. Are there other aspects of ignition likely?

 

As to the air temp sensor, where is that located? I imagine I could check the reported temp through the obd2 output, to see if accurate.

 

When you say "haven't been changed", you can't be meaning 12 years ago, can you? As with any ignition system, pay attention to plug wires as well. Look for any cuts, breaks, chaffing, etc on the wires. You can also try spraying the wires with water and engine running. The best way to see if there any concerns with wires, spray with water, and put the truck someplace where it is dark. By dark I mean real dark, no source of light nearby. If wires are starting to breakdown, you should see it with really dark area and a water mister.

 

If you have a scan tool, it is best to plug it in before your cold morning startup and turn the key on, record the values for any sensor that has temp in its name. Should see readings that reflect the actual temp.

 

If the plugs are original, it is long overdue for a change.

[mike_2001]

Thanks Doug. I need to check my records, but I think that's the case.

[mike_2001]

An update: I replaced plugs with NGK 3186 platinums, 0.040 gap. Existing plugs were worn to about 0.065 or worse. Tried to start this morning at about 7 degrees, and had a tough time. After the first two or three tries, I installed the fuel pressure gage, and pressures appeared to be above 55 psi. I finally got it started after about 10 tries. I ran the engine for 5 minutes or so, and tried to restart. It didnt restart, so I hooked up the OBD scanner. The coolant temp read 80 degrees (after a few minutes running) and the air intake temp read 14 degrees. No codes on the engine, other than 4 related to the EVAP system (P0446, P0442, etc). When I am able to start it in conditions like this, it runs fine as soon as it fires no running rough, etc, so I doubt it would be a leaking injector or similar.

The fuel filter was not replaced with the fuel pump swap, and is due. But, I havent seen a fuel delivery issue at any speed while it is running, so I doubt that is the problem.

In a post earlier, you mentioned checking the battery voltage when crankingwhat should that value be?

 

I am wondering what to try next.

[txab]

OEM plugs were gapped at .060". They changed to .040 around 2004

[Doug_Scott]

I am not sure what is normal in EFI engines, but, it used to be above 9 volts when cranking over. I would expect over 10 volts The lower the voltage, the less power for ignition.

 

If you have one handy, you may want to try boosting the truck and see if it starts faster. You would need to set this up the night before, back your truck in, then put another vehicle nose to nose with your truck. In the morning, try to start truck once or twice, then if not started, boost from other vehicle. That will get you enough voltage to start your truck, if that is the issue. If truck starts, you know where to look. If it doesn't, then you know where not to look.

[mike_2001]

Good idea. I think I'll use a battery booster pack instead,

[mike_2001]

I tried it with the booster pack at zero degrees. Cranked very nicely, but wouldn't start after three tries. After a half hour, i tried it without the pack, while measuring voltage. It started first try, and voltage dipped to about 10.8 volts, I believe.

[Doug_Scott]

Battery is likely ok, but, try chccking voltage without the booster on a cold start. Since it will fail to start sometimes, that is when you need to check voltage with booster.

[mike_2001]

I took it to my local mechanic, who discerned that it wasnt getting adequate ignition voltage, only on certain positions of the ignition key. When he just crept up on the starter, barely turning the key, it would start first try. When the key was cranked all the way forward, the vehicle wouldnt start. The second method of turning the key is my default, by the way.

It appears that there is a high-resistance spot on the switch, which causes just enough voltage drop to interfere with ignition on very cold days.

Wow. I would have never found that.

 

How difficult is replacing the ignition switch?

[Doug_Scott]

There is more to it than just the switch. Going back to old style ignition systems, the ignition actually ran on 9volts, and used either a ballast resister or a resistor type primary wire. During cranking, the ballast resister was bypassed so ignition system would still get enough voltage. One of the tricks to getting a Dodge back to the shop when the ballast resister burnt out was to not turn the key fully to the start position, and when engine started, roll back key until the starter disengaged. You could then drive the car as long as the key was turned just far enough to keep it running, yet not far enough to engage starter.

 

Ths give away that this was the issue was the car would fire up, but then quit as soon as key was released. It would always fire up. Just would not stay running.

Your truck was not firing at all wasn't it?

Should be easy enough to verify it is the switch, use a ohm meter to check resistance in the switch. I would be checking before swapping the switch.

[mike_2001]

During those circumstances, it would not fire at all. Good idea on checking the resistance. Any idea on which terminals to check? I suspect it would be the connector just under the lock cylinder,

[Doug_Scott]

You would need a wiring diagram or at least a pinout for the connector on the ignition switch. The more I think about it the less I see it being the ignition switch. The ignition switch should not be carrying enough current to effect the ingition system voltage, The switch should just be triggering other systems to start the engine.

If the truck is starting every time now if you handle the switch just right, you may want to look at the adjustment of the actual switch. Perhaps in very cold the switch becomes slightly out of adjustment, and when it warms enough, the switch moves back into adjustment.

 

Seems far fetched, but, think about it, on trucks equipped with remote start, it can start a truck without any movement from the actual ignition switch. To me that means the ignition switch does not carry ignition system current. If it did, it would be needed for remote start to work.

 

Perhaps there are others here that have more current knowledge of ignition switch logic.