1997 CHEVROLET SILVERADO COLD START PROBELM

pepe

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#1
We are trying to figure out a problem with this Silverado truck 5.7 Eng with 115,000 miles on the meter. The problem is when the truck has been off for quite a while engine completely cold it will not start. There are no codes or pending codes present, We check fuel pressure, spark, all the basics and found nothing wrong. I stomp on the gas pedal to cut the fuel to see if it will start but nothing. The only way the truck will start is we keep holding the ignition key in the start position for few second then off pos. then start positing again, engine starts to stumble and finally starts. When the engine is running it sound normal no signs of hesitation or anything. when the engine is at normal
temperature it will start right up every single time until the it completely cold
again. The
only two thing I can think of is either the crank sensor or an ECT problem. The reason I mention ECT [engine coolant tem sensor] is because when I test the connection with my volt meter I don't get a 5v reading when ignition key is turn to ON
position it stays at 1.40v sensor disconnected. Any help or anybody familiar with kind of problem please help I appreciated and Thanks in advance Question: Do these engines have a cold starts injector ? :-\
 
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#2
Is the check engine light blinking or on?
Any stored codes?

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
 

pepe

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Crunch- No check engine light ON or blinking and pending codes as well. I even took the truck for a spin at cruise and freeway with my scannner in live data dispaly, everything seems to be working properly ran all monitors and MIL did not turn ON. With the fuel pressure guage hooked up early morning first start I get good reading 55psi according to Chilton Manual its OK but I see you mention 65 at least for the injectors to squirt ::). But again it only happens when the engine been off for at least 4-8 hours or early morning cold first start. You know It kind make make think we have a fuel problem delivery here! The reason I say that is because " Why does it have to wait so long so problem can be duplicated??
 
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#4
On a cold start you have to have 64-65 lbs of fuel pressure to squirt the injector.
Even a couple of lbs low will give you problems.
After warm up they will start and run all day with low fuel pressure.
May not run right but will run if not to low.
The longer it sits the cooler it gets and more fuel pressure it has to have to start.
Better pitch that Chilton manual in the trash can.
I would also go threw the complete fuel pressure test.
Hot and cold and drive down the road with gauge taped to outside windshield or mirror.
But remember it could be a fuel regulator or fuel pump.
The test will lead you in the right direction.
Crunch
 
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Coyote

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#5
Had same problem with my GMC a while back. Turned out to be distrubor cap and rotor
 

Transman

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Agreed with Crunch here, We have had many GM problems from hard start to missing all due to 1 or 2 pounds light from the fuel pressure. The Vortec engines are also well known for filling up the intake with fuel from a bad pressure regulator assy.
FWIW, if you end up pulling the upper plenum to go there, pay a few extra bucks for the updated injectors from GM. It's a kit and well worth it as it turns those crappy poppets into real injectors. Transman
 

pepe

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OK great thanks guys I just got back in town from camping I will double check fuel pressure again make sure I got the correct reading. Now the fuel pressure regulator is it located internal if the intake or out by the fuel lines? Thanks Again Pepe I will keep posted
 

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#8
The Vortec engine stores the pressure regulator and injectors under the plastic plenum. It's really not a bad job to get to it but check your pressures first because a fuel pressure relay can cause the same symptoms. GM uses a backup relay in the oil pressure switch that will activate the fuel pump as soon as it sees oil pressure.
If you are interested in the TSB that gives you the part numbers for the update kit then I will post them for you. Transman
 

pepe

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OK Here we go first thing in the morning got my fuel pressure gauge with one the reaches to the windshield so I could monitor the pressure at different speeds and loads. Here is what I got

First start cold n the morning 53-55 psi no more. I did what I mention above to starts the engine and the reading did not change.

Warm Idle cruise 54-55psi no load

Warm at freeway 59-60psi no more

Deceleration hit 50-53 psi

Full Throttle below 60psi no more

Low cruise below 54-60psi

I shut off the engine completely ignition off and I seems like there is no leak down in the fuel system because pressure remain the same for quite a while at 55 psi.

During all these testes finally something came on the Check engine light!! pull the codes and got :::
P0131 signal low bank 1 sensor 1

P0151 signal low bank 2 sensor 1

Freeze frame:

RPM 3737 Fuel System B1 OL
Fuel system B2 OL Coolant 108[C*]
Air Flow 133.23 MAP [kpa] 99
ST Trim B1[%] 0.0 LT Trim B1[%] 9.4
St Trim B2[%] 0.0 LT Trim B2[%] 9.4
Vehicle speed 61 MPH Engine load 64.8

I believe the system is running slightly lean on both banks due to bad fuel pump insufficient fuel pressure what you fellas think I hope these results help.
 

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If your fuel pressure gauge is accurate then you have a fuel pressure problem. You can test no further until you have resolved that issue. As i stated before, as did Crunch, later GM vehicles will not run right with even a few lbs below operating pressures. Have you replaced the fuel filter and checked the pressures? If so then the next step is to check if the fuel pump can deliver the pressure needed. You will need a fuel pressure gauge on the system and pinch off the return line for just a moment and see what the pressure drives up to. If it goes way up then the problem is most likely the regulator. At that point I would recommend the update kit. If not then examine the fuel pump as the primary culprit. Post back with results, Transman
 

pepe

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Transman about pinching the return line if pressure goes way up.. What reading is way up to you, Crunch stated when If I pinch the return line it should be 75-85 or way more I am a bit confused ???   Also in addition again I tested in cold start this evening and this time I only turn on the switch to ON position and the reading is only 55psi and still didn't want to start on the first couple tries, I tried two different fuel pressure gauges to make sure my reading are correct. Transman or fellas?? ::)what should I replaced?? Is my question.. Tomorrow I will swap in a new fuel filter and recheck readings also will pinch return line and post down reading
 

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#12
Definition of "Way Up" will basically be well over running pressure, I have seen them hit 150 psi but you are looking for a brief pinch and a big rise. If the pressure remains at the same pressure as running then something is wrong with the feed side of the system, pump, filter, pinched feed line, clogged sock or trash in the tank itself. If it rises nicely then the pump is capable of delivering the pressure required but the regulation circuit is not asking for the pressure. Common problem at that point is the regulator itself. Hope that helps answer the question, Transman
 
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I see now Trans what you mean I see!! OK did not have time today but I keep posted with result, I believe that this will basically tell me if its the fuel pump or the regulator is the problem :-X....Just got that feeling that its the regulator "spyder" is what they call it..
 

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#14
Yes, The regulator is the spider under the plenum together with the injectors. If you look under the plenum and see gas just laying there then it's bad. This is where you put the upgraded injector kit in there. The regulator assy comes with the new injectors. I will post the part numbers if you need to go there. Transman
 

hector85

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#15
just finished working on a 97 plymouth grand voyager with a 3.0 v6 that had the same problem had spark fuel except for compression you might want to check compression the van ended up having bad rings van did exactly what you explained hard to start when cold would only crank by leaving key forward and would start and run great when at operating temp