Please help....my 99 Tahoe has suddenly decided to give me problems. Starts right up in the cool morning, but when I crank it after it's been sitting outside while I'm at work, (hot days) it turns over and dies immediately. Crank it again, and it starts. Took it to the shop and they said it needed tune up. Ok, replaced wires, rotor, cap, plugs were ok. Didn't work, it still did this. Checked the fuel pressure and it held fine. Fuel pump is running, it was replaced this past spring. Replaced the ECT sensor, so that's new. O2 sensor, I was told was fine as well. New battery, starter this spring too. No codes are being shown for any kind of trouble. Could it be the ignition module? I don't really want to start replacing everything on the off chance that might be the problem, expecially since I've replaced so much as it is! Anybody run into this? Got a fix? :banghead:

Please help....my 99 Tahoe has suddenly decided to give me problems. Starts right up in the cool morning, but when I crank it after it's been sitting outside while I'm at work, (hot days) it turns over and dies immediately. Crank it again, and it starts. Took it to the shop and they said it needed tune up. Ok, replaced wires, rotor, cap, plugs were ok. Didn't work, it still did this. Checked the fuel pressure and it held fine. Fuel pump is running, it was replaced this past spring. Replaced the ECT sensor, so that's new. O2 sensor, I was told was fine as well. New battery, starter this spring too. No codes are being shown for any kind of trouble. Could it be the ignition module? I don't really want to start replacing everything on the off chance that might be the problem, expecially since I've replaced so much as it is! Anybody run into this? Got a fix? :banghead:


please give the detailed engine discription and miles ..

I'm just guessing that with no codes its the cps...when hot they tend to fail does your tach jump intermittently? if so the cps/or wires grounds in that circuit..

Thanks for reading...
Ok, brief history here...this is not the original engine. This engine is a NEW engine put in about 3-4 years ago, has about 60,000 on it now. the old one broke the crankshaft. The cps was replaced along with putting the new engine in. (not a rebuilt engine, we actually managed to find a new one in the crate and the dealer put it in) Oh, and it's the 5.7 liter V8.
The tach does not jump. I've tried to watch it, thinking along the same lines as you possibly and it doesn't jump. Runs smoothly, idles smoothly. Starts perfectly with no hesitation in the morning, when it's cool outside. Just started doing the hesitation and dying after sitting out in the hot sun when I'm at work. Then it cranks, acts like it's going to start, and dies immediately. When I turn the key the second time, it starts, but seems to hesitate, as if something that should take over and keep the engine running isn't 'grabbing' it quickly enough, but it takes hold and then it starts running. This is only a couple seconds of hesitation. If I wasn't paying attention, I'd miss it. When we replaced the fuel pump, we replaced the entire assembly. Even made sure the connecting wire had a good end on it. I just can't figure out what this problem is. We put a scanner on it and it's just reading all is ok. Does not pull any codes at all. Never had this problem before with any vehicle ever. Just started late August and it was sporadic. Today it started fine after work no problem. Stopped at a store and it did the dying thing when I got back into it. Weird. Any other ideas? Or could the cps be going bad so soon? And how could the cps be hot when the vehicle hasn't been running, as when it sits all day? Appreciate any help you can offer!
Oh, and we replace the ignition module just yesterday and that didn't solve it either.

[quote=m1009]Thanks for reading...

with all that I would suspect the ECT as this also will not generate any codes...check resistance cold/hot and compare...if the computer is told that the engine is hot and its cool the injectors won't stay open long enough ...you have checked the fuel pressure and that is normal and it always starts cold...so the ECT is suspect...

We replaced the ECT and that did NOT solve the problem. Also replaced the ignition module and that didn't help either. Hoping to find a fix before having to spend some money to try and get a diagnostic done at the dealers. Thanks for that idea , anyway. It always starts on the second try too, if that helps any. :banghead:

We replaced the ECT and that did NOT solve the problem. Also replaced the ignition module and that didn't help either. Hoping to find a fix before having to spend some money to try and get a diagnostic done at the dealers. Thanks for that idea , anyway. It always starts on the second try too, if that helps any. :banghead:


when you start engine turn key to ignition on , wait 2 seconds then crank ....it should start up immediately...it may be the fuel pump needs more time to produce the required pressure...

If this solves the problem the fuel relay and the frame rail ground next to the fuel tank may need replacing /cleaning...

Well, I always wait a few seconds to make sure the fuel pump is pressurizing. We've had trouble with the fuel pumps on this vehicle before, so one of the things we've got used to doing it waiting to make sure it's running before turing the key over. This is actually the 3rd fuel pump, as the original failed about 4 years ago and the one they put in was defective, so technically this is the 3rd one. Made sure the connection wasn't corroded, and made sure that plug in was good. Not sure of the name of it, sorry. It's just weird. It definitely is running, and I have tried the trick of hitting the gas pedal on that first start try to see if that would help and it doesn't do a thing. Still dies. But of course, the second try it fires up. Even tried something yesterday, we gave it some more gas just before shutting it off, and then restarted it, and it acted like it was flooded this time. So, I don't think its a fuel starvation issue. I feel as if it's something to do with controlling the actual idle from the initial start phase. But if the idle contol looked ok,and seemed to move easily when we checked it, could it still be bad? Am I thinking right? Thanks for all your efforts, and thoughts. Appreciate it, helps me kind of work through this step by step.

Well, I always wait a few seconds to make sure the fuel pump is pressurizing. We've had trouble with the fuel pumps on this vehicle before, so one of the things we've got used to doing it waiting to make sure it's running before turing the key over. This is actually the 3rd fuel pump, as the original failed about 4 years ago and the one they put in was defective, so technically this is the 3rd one. Made sure the connection wasn't corroded, and made sure that plug in was good. Not sure of the name of it, sorry. It's just weird. It definitely is running, and I have tried the trick of hitting the gas pedal on that first start try to see if that would help and it doesn't do a thing. Still dies. But of course, the second try it fires up. Even tried something yesterday, we gave it some more gas just before shutting it off, and then restarted it, and it acted like it was flooded this time. So, I don't think its a fuel starvation issue. I feel as if it's something to do with controlling the actual idle from the initial start phase. But if the idle contol looked ok,and seemed to move easily when we checked it, could it still be bad? Am I thinking right? Thanks for all your efforts, and thoughts. Appreciate it, helps me kind of work through this step by step.


you replaced the ECT did you check the resistance and compare with the original...this is what I would do ..then place in boiling water and check resistance..

The IAC should not move freely and it is stated that you must not force the IAC to move as this will damage it...also do not use any carb cleaner on throttle body...carb cleaner will damage throttle body and other componets...


when starting the injectors should stay open longer this then will cause the IAC to allow more air to enter the intake manifold an then the idle is higher. this is to keep the engine running with the proper air/fuel mixture... if the IAC is broken it cannot do that..


IF the IAC where broken you would have engine stalling all the time as this device is what keeps idle proper ...does your idle stay at 650rpm ....?


if it drops to 300-400rpm on tach the IAC is most likely bad..

my vehicle and the others , that have this idle control , when engine at normal temp, will keep idle within 50rpm of 650....


when first starting the idle should for a brief time go to 1200rpm....then slowly drift down to the 650....

Hmm, thanks for your input! I'll have to check out the rpm tomorrow and see. When we checked the idle control, I don't think we forced it, but maybe it's going bad? We did see that it looked a bit gummed up. Would it just fail suddenly? Engine is not stalling at all, as I mentioned, it runs smoothly. No hesitation, no tach jumping, no problems in acceleration.
We didn't bother checking the resistance between the old and new ECT, however. Is there any other sensor, valve, etc that might have an effect on the startup that I might be missing?
I will have to watch to see where the idle is on the tach when it starts though. I'll post again with any results I find, somehow we'll figure this out!
Thanks so much for your ideas, really appreciate all the input!

Well, when starting a cold engine the tach went to around 1100, 1000 and then dropped off slowly to about 800 or so. On a warm engine it didn't go that high, stayed to just below 1000 when starting up, and I really didn't let it run much as, of course, I wanted to get home after a long day at work! Is it possible for the idle control to start going bad? Or does it just quit suddenly? Thanks again.

Well, when starting a cold engine the tach went to around 1100, 1000 and then dropped off slowly to about 800 or so. On a warm engine it didn't go that high, stayed to just below 1000 when starting up, and I really didn't let it run much as, of course, I wanted to get home after a long day at work! Is it possible for the idle control to start going bad? Or does it just quit suddenly? Thanks again.


well with what you have given, the idle of 800 when warm , is too high.. this usually is a vacuum leak /too much air getting into the intake ...this could be a worn PCV or hoses to a defective intake manifold/gaskets and other componets..

Well, we dropped it off at the dealer today. From 7 am to 4:45 pm and they still couldn't diagnose it completely. The scan tool did not find anything wrong. The only thing it 'might' be is either the fuel pump is going bad again, or the fuel regulator might be going bad. The fuel pressure held steady at 62 and they had trouble getting it to act up consistently. The only thing, when hubby went there to pick it back up, he spent about an hour with the tech and they were going over some of the problems, he was watching the pressure gauge again, and just once, the pressure did not spike the way it should. The tech said that it seems as if it's not consistently spiking when it starts, and that might be causing the starting problem. But, again, it's not consistant. Couple things we can try to isolate it, at least we have some more ideas. Hubby's going to get a fuel pump pressure gauge kit and we'll hook it up so we can monitor the pressure each time we start it. He's got an idea of how we can narrow it down to see what part might be going bad. Sorry my terminology isn't the greatest, so I might be leaving some stuff out but I'm not the mechanic, I just know a little and hand over tools...:smile:
If we figure it out, I'll post it here.

Thanks for all your help!

Well, we dropped it off at the dealer today. From 7 am to 4:45 pm and they still couldn't diagnose it completely. The scan tool did not find anything wrong. The only thing it 'might' be is either the fuel pump is going bad again, or the fuel regulator might be going bad. The fuel pressure held steady at 62 and they had trouble getting it to act up consistently. The only thing, when hubby went there to pick it back up, he spent about an hour with the tech and they were going over some of the problems, he was watching the pressure gauge again, and just once, the pressure did not spike the way it should. The tech said that it seems as if it's not consistently spiking when it starts, and that might be causing the starting problem. But, again, it's not consistant. Couple things we can try to isolate it, at least we have some more ideas. Hubby's going to get a fuel pump pressure gauge kit and we'll hook it up so we can monitor the pressure each time we start it. He's got an idea of how we can narrow it down to see what part might be going bad. Sorry my terminology isn't the greatest, so I might be leaving some stuff out but I'm not the mechanic, I just know a little and hand over tools...:smile:
If we figure it out, I'll post it here.

Thanks for all your help!


since this is intermittent and the vehicle is about 10years old replace the fuel pump relay....this is about the life expectancy..also recheck the ground wires next to the fuel tank which means remove,and wire brush the frame rail so it shines and re attach these ground wires...

Knew it wasn't the relay-We took it home, managed to work on it today-hooked up the pressure gauge and tried all different scenarios to see what happened. At first the pressure seemed consistent-let it cool off and tried again. Suddenly it didn't want to build pressure. Then it would build it correctly. We removed the return line from the pump and checked to see if the regulator was working-no fuel came back to the tank, so it was ok. And the pump running, so somehing was wrong. We had already checked the wiring and were getting voltage. Since the regulator was working, it had to be the pump, and then it stopped running a couple times, so we knew that the pump was failing. So, pump replaced, starts up great and it was under warranty too. Thanks for all your help, ideas were great!
Wanted to let you all know we fixed it! :grinno:

Knew it wasn't the relay-We took it home, managed to work on it today-hooked up the pressure gauge and tried all different scenarios to see what happened. At first the pressure seemed consistent-let it cool off and tried again. Suddenly it didn't want to build pressure. Then it would build it correctly. We removed the return line from the pump and checked to see if the regulator was working-no fuel came back to the tank, so it was ok. And the pump running, so somehing was wrong. We had already checked the wiring and were getting voltage. Since the regulator was working, it had to be the pump, and then it stopped running a couple times, so we knew that the pump was failing. So, pump replaced, starts up great and it was under warranty too. Thanks for all your help, ideas were great!
Wanted to let you all know we fixed it! :grinno:

thats great that you finally repaired this.your problem is odd...usually if the fuel pump is bad the fuel pressure check will show the loss of pressure...This symptom that you had says bad feed/ground power supply to the fuel pump motor...even the dealer , testing could not determine the failure...intermittent problems most always are wiring..or other control devices....