Extended Cranking Time When Cold

majorxlr8nSeptember 26, 2008

I have a 1996 Chevrolet C1500 extended cab pickup with a 5.0 liter (305ci) V8 and an automatic transmission. Truck has only 60k miles. Lately, I've noticed that I must allow the starter to run longer to get the engine running when cold. Starts promptly when hot, and runs well otherwise. The check engine light is not on, and I have had the ECM scanned for codes and none are present. How should I proceed with troubleshooting and correcting this?

Much thanks in advance!

Marty

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paparoseman

If it has throttle body fuel injection like my 1990 has it could be a clogged,inoperative injector. Mine just came out of the shop after getting one replaced. Started great when warm but the first cold start took extra cranking.

    Bookmark   September 26, 2008 at 7:18PM
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majorxlr8n

Thanks for the reply. I guess that makes sense, but if the injector was truely bad, wouldn't the engine stumble or hesitate upon acceleration when cold? Once my engine is started, the truck exhibits no cold drivability issues.

Regards - Marty

    Bookmark   September 27, 2008 at 12:12AM
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john_g

You need to start with the basics here. You are either missing, or have incorrect fuel, or spark.

Starting with spark, use a tool called the ST-125. Just trying to make the spark jump from a screwdriver isn't enough. The ST-125 looks like a spark plug with an alligator clip on the side. It takes 25,000 volts to jump it's gap. If an engine runs, and the ST-125 is in one of the plug wires and it is not firing, test as no-spark.

The second thing you need to test is fuel. You could have fuel pressure, meanwhile the engine is not actually getting enough fuel delivered to it through the injectors, so there are several steps to take.

The first is scan data, ensure sensors like the ECT, and IAT display the correct temperature as compared to ambient temperature after the car has been sitting a few hours to allow everything to cool and stabilize.

You need to check fuel pressure, and you NEED TO USE A GAGE! In fact a very accurate gage. At 54 psi your truck will not start. At 55-56 psi it will.

Let's see how far you get from here.

    Bookmark   September 27, 2008 at 8:58AM
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majorxlr8n

John - thank you for the detailed cyber diagnosis. I don't have a true scan tool - just a code reader. So what I'll end up doing first is checking with my spark tester, then checking fuel pressure. I still have a very accurate DFI gauge from when I used to adjust the fuel regulator on my Buick Grand National...

Regards - Marty

    Bookmark   September 28, 2008 at 7:55PM
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greentfinger

You might try the cold start valve & feed. If valve is working properly check engine light will not come on however if fuel feed through or to the valve is impeded light will fail to light.This, cold start valve, supplants the old choke on older cars.

    Bookmark   September 29, 2008 at 12:14PM
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john_g

HI "Green"

The cold start valve was a typical device found on the earlier injection systems, and was usually paired with a device called a thermal time switch. During cranking this pair of components did add additional fuel to the engine to assist in starting. Later years had some models only using a computer controlled cold start injector. Today's cars, especially domestics control emissions to such an exact level that the cold start injector system simply was not feasible to continue. Plus the systems are sophisticated enough that it is also no longer necessary anyway. Majors truck does not use a cold start injector. In truth though, if it did I'll give three to one odds it would actually start easier because of the problem he is having!

    Bookmark   September 30, 2008 at 8:40AM
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kalining

Your not kidding,John. been a long time but i think it was a chevy S10. Neighbour called me over because of no start.
I could hear hhis fuel pump from my place. 4 houses away.
Asked him when the last time he changed his fuel filter.
( first thing i sak ). He said " what filter ". Well, here
we go. you can kiss that pump good by. Changed the filter only because he was too cheap to replace the pump. Pump
quieted down a little. 35 lbs in the rail. Refused to start. MADE him spend money to replace the pump. We got 37
lbs and away it went.

    Bookmark   September 30, 2008 at 10:47AM
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greentfinger

John_g:Yeah I guess there have been many changes since I sold my toolbox(1990). Cold start valves were quite a problem on the earlier fuel injection systems as you said. Now if you asked me to solve a fuel problem on cars prior to 1990 I MIGHT be able to, before 1980 YES, no problem.

    Bookmark   September 30, 2008 at 3:48PM
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majorxlr8n

Thank you all for the replies! I've been on vacation & haven't had a chance to look at this yet...

However, I had to use the truck today. It had been sitting for 13 days. It was a bear to get going. It took about 5 attempts to get it running. The idle RPM was ultra low & it kept stalling.

I have to get at this VERY soon. I don't want to be stranded. She's telling me SOMETHING IS WRONG...

Marty

    Bookmark   October 10, 2008 at 12:11AM
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majorxlr8n

OK - I hooked up my fuel pressure tester. The truck sat a good 11 hours so it was cold. I turned the key ON and got 19.7 psi. I then turned the key to CRANK and thats all it did for about 6 seconds. The pressure did drop during cranking, but finally went up to 61.3 psi & it started. Fuel pump time? Or could a neglected (sic) fuel filter be at fault? Once warm. it maintains between 58-61 psi.

Thanks guys - Marty

    Bookmark   October 10, 2008 at 5:46PM
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john_g

Now repeat the exercise while measuring the current flow through the fuel pump circuit and you will have your answer as to whether this is a pump, wiring issue, or fuel filter problem (Not likely to be a filter issue but regular service is still needed)

Using a low amps probe and an oscilloscope I not only measure the pump current draw, I can read the actual speed of the pump.

    Bookmark   October 11, 2008 at 9:48AM
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majorxlr8n

I found out that there is a check valve in the pump that helps maintain pressure when the fuel pump is at rest. So I went to release pressure at the fuel rail service port (cold) and there was NONE present. I went ahead & replaced the pump and the truck is starting up MUCH better. Upon removal, I noticed that the old pump was missing a red/orange "umbrella" check valve, where the new one has one installed. The pressure now holds 59 psi almost all the time and I can now actually hear the pump "buzzing" again.

Thank you for all the input!
Marty

    Bookmark   October 16, 2008 at 12:56AM
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