97 TAHOE 5.7L VORTEC WON'T START...GM Merlin ideas?

[techmike]

I have had the same problem lately with the Vortec 5.7 in my '97 Tahoe. It has 192,000 miles. Runs Great! Shut it off, and sometimes won't start back up!

Anyway, the other day I was driving and came to a stop sign. It DIED! Then the usual, cranking and cranking...still nothing.

For the heck of it, I unscrewed the gas cap, cranked and fired right up! Fuel pump was just replaced. Wires and distributor are new.

Can anyone else try this when theirs does this? Was it just a fluke?

[ERICWILS]

After you replaced your crank sensor did you have to perform a crank relearn prcedure?

[Chetco]

Thanks for all the ideas since mt 99 tajoe is turning over but not starting.

[motobtn]

Hello All-
So I have to say thank you for all of you who have posted so far, these forums are very helpful.
I am having a very similar issue, and could use some more help.
I recently purchases a 98 5.7L K1500 that started fine when I first picked it up and has had issues ever since. It will crank and crank, almost fire, sputter, but not fire. I started by trying the basics, cam and crankshaft sensors, timed it, and replaced the fuel filter. Nothing worked, until I got it into the garage and heated it up and it started right up. I had heard great things on the MFI conversion, and decided I would try that first, even knowing my fuel pressure was a little low, 52-57psi, because the new Delphi Fuel Pump was only about a year old and I thought the new MFI system might not need as much pressure as the stock SCPI. Did the conversion, and the thing started great for a couple days, then back to the same crank and crank with no fire. So I dumped a can of HEET in just to see what happened, and she roared on barely touching the key. At this point I though maybe bad gas, but it didn't start a couple days later, so then I thought maybe it was the extra octane that compensated for low fuel pressure. So i replaced the fuel pump, and it started for 2 days, and now I am back to no start! I don't really want to just THROW parts at it, but if this is all I have left, then maybe I will.
So here are my thoughts on the last of the possibilities. Please let me know where you would start.
1) Weak Coil
2) Bad Rotor
3) Bad Cap
4)Throttle Position Sensor
5)Temp Control Sensor...CTS right?
6) IAT sensor
7)Compression

Once it starts, it runs great, but it is cold here now and every time it doesn't start, I scramble to get another ride etc to work, and want to know what fixed it when I fix it.

Please, any thoughts would be great on trying to narrow it down as all these parts would be a couple hundred. Also, haven't looked at the compression yet, but does anyone else think that makes sense. A guy at chevy suggested I check that, but I have never read anything about that in all the forums I have been looking at lately. His theory was if I have bad compression, it means that the rings aren't sealing and the gas is just flowing around. This doesn't quite add up to me based on that when it starts it runs so well and I get no codes, but maybe I am wrong here.

Thanks!

[j cAT]

poor cold start and no codes can be low fuel pressures or the ECT/CTS coolant sensor to the computer/pcm/vcm is out of spec.

also connections to it.

after warm up it runs fine..how can it be compression or other engine problems ?

old contaminated fuel the kind we use now will cause poor cold start if a few months old.

[motobtn]

I agree that it is hard to believe it is compression, but he was trying to tell me that once it fired the pistons rings would warm up and seal...basically BS to me which is why I came here for more opinions!

It isn't low fuel pressure as I am at 60 and above now with the new pump, and the new MFI injectors have a new fuel pressure reg with them. There is fresh gas in it, and the other tank got a can a HEET, so I think the gas is ruled out unless is was REAL bad...but I am not sure how that would happen.

I will replace the ECT first I think, then Dist. Cap, then rotor.

I mean the thing runs wonderful when it starts, and sometimes it starts dead cold, but once it doesn't start, it doesn't start until it warms up again is what I have experienced so far. I am going to try and get work done on it tonight or tomorrow night, and will post results as they come. I won't know anything for sure, as the last couple times I have thought it was fixed, it only lasted a day or two, but I will still keep up the posts as time goes on.
However, and more comments are definitely welcome.

Thanks again everyone!

[j cAT]

the ect is about 20.oo...if it is original its most likely out of spec.

I always replace the distributor cap and rotor as a set made by the same manufacturer.

bad cap/rotor/distributor etc would cause poor high rpm run. as the arcing would be created at the higher rpm.

[motobtn]

Well, new cap, rotor and cts...no go. Unplugged the battery to see if it "resets" everything. I just don't get why I would replace the cap and rotor when I have spark. Should I try the cool or wires for spark quality?!
Thanks for all the help!

[j cAT]

Originally Posted by motobtn

Well, new cap, rotor and cts...no go. Unplugged the battery to see if it "resets" everything. I just don't get why I would replace the cap and rotor when I have spark. Should I try the cool or wires for spark quality?!
Thanks for all the help!

you stated you where going to replace the cap ////then rotor ///// all I stated is when you replace cap you should also replace rotor of the same manufacturer and I added this would in most cases not cause a poor cold start ....these if bad would cause problems at the higher rpm.

the spark quality if bad would cause engine to throw codes and run like crap........

the coolant sensor will screw up cold start...............

[motobtn]

I apologize, I didn't mean to come off upset about installing the cap and rotor. I have been told by many it has fixed the problem, so for a few bucks why not. The coolant sensor is replaced now too, any thing I need to do to initialize it or relearn it or anything. Could the engine be flooded from extended cranking by now and need to sit over night?
I truly do appreciate the help, just running out of stuff to try!
Thanks!
Adam

[j cAT]

Originally Posted by motobtn

I apologize, I didn't mean to come off upset about installing the cap and rotor. I have been told by many it has fixed the problem, so for a few bucks why not. The coolant sensor is replaced now too, any thing I need to do to initialize it or relearn it or anything. Could the engine be flooded from extended cranking by now and need to sit over night?
I truly do appreciate the help, just running out of stuff to try!
Thanks!
Adam

see if the plugs are fouled. see if wet with fuel and black.

check fuel pressure again with key on engine off and see if the fuel pressure holds and not drops off. if it drops off this may mean injectors leaking. this will flood engine.

[j cAT]

Originally Posted by motobtn

I apologize, I didn't mean to come off upset about installing the cap and rotor. I have been told by many it has fixed the problem, so for a few bucks why not. The coolant sensor is replaced now too, any thing I need to do to initialize it or relearn it or anything. Could the engine be flooded from extended cranking by now and need to sit over night?
I truly do appreciate the help, just running out of stuff to try!
Thanks!
Adam

on your vehicle you need 60-65psi fuel pressure. not sure you are aware of this.

[motobtn]

The fuel pressure when key on, engine off is 60psi.
I ended up letting the battery charge last night with the neg. term. disconnected, and then cranked on it for about 10sec at 9pm and it fired up! (this has happened in the past after I have had trouble starting it...would this essentially be flooded?! It had sat for about 3 hours before this latest attempt to start) Anyways, got it started this morning again after a night of sitting outside, not too cold, but probably high teens.
I am going to try starting after work again, then again in the morning, and repeat process for a couple days before relying on it to drive as this has happened this same way several times before now.

My biggest question at this point is this. The truck didn't start yesterday morning, and I cranked on it a decent amount. I then cranked on it a bit when I got home 10 hours later, with no luck and a weaker battery. I changed the CTS, put the charger on for a bit, no start. I changed the cap and rotor, still no start. I disconnected the negative again hoping it would reset the PCM which I was thinking might need to happen to "Recalibrate" itself...if it even does this. After sitting for 3 hours with the neg. detached and the battery well charged, it took some cranking, but fired up.Does this make sense that this would happen, or am I going to be stuck without start in a couple days?

Anybody want to take a guess here? I am 50/50 to tell you the truth as this same thing has happened a few times now.

I will check plugs next and probably throw a new set in just because it is easy and that would give me a new BW rotor, BW cap, and plugs, with relatively new BW wires...new fuel pump with ground connection cleaned and spray painted with rustoleum to help prevent rust, new MFI conversion, and a new CTS, Cam Sensor and Crank Shaft Sensor! If this doesn't work, I will get back to you and let you know. Thanks again for all the help, and any other thoughts or test would be great to hear. I will probably try to test all the components I pulled the best I can to determine what was actually bad and what was in spec. My hunch is a few different things were playing badly together and if I hadn't changed them now, I would have down the road...ie fuel pump, injectors, CTS.

Thanks again to all for their help, and hopefully this will help others as much as others have helped me!

[j cAT]

with key on and the engine off , the fuel pressure must be 60-65psi. and hold for 15 min or so. if it drops off more than a few psi then this may indicate the injecotrs are leaking or other items reg/fuel pump.fuel line.

[motobtn]

Thanks! I definitely didn't wait that long to see if it held, so I will check that and post back if it drops. I will say, I was expecting closer to 65 with a brand new pump and filter...