99 Tahoe 5.7 won't start

[BillPete]

Have a 99 Tahoe (159k mi) that intermittently will not start. If it does start, runs fine, as normal. This began about 2 months ago on a cold damp morning 350 miles north of home on a fishing trip. I ran the battery down trying to start it, saw that it was past warranty, bought a new battery and the vehicle started right up and behaved fine for about 2 or 3 weeks. I thought my problem was solved as I had just gone through the same problem with my wife's 99 Yukon that is virtually identical in options and drivetrain to the Tahoe. They are both loaded with all electric options. The Yukon has been fine since installing a new battery.

When the Tahoe wouldn't start at home on a rainy morning, I began to suspect cap and rotor and replaced them. Made no difference. Someone advised me to test the alternator as it may not be charging the battery fully. It tested fine by a tech who actually rebuilds them, took it all apart and said everything is good, including regulator.

I read about smacking the gas tank to test your fuel pump, did so and was up and running again. This fuel pump has about 40k miles on it as I had it replaced at about 120k. The mechanic assured me that I did not want to buy OEM and gave me a "deal" only charging me $300 for an aftermarket one, from what I've read, most likely an Airtex which does not seem to be a good one at all. I've since found that I can buy pumps for anywhere from $100 to just over $300 from a variety of manufacturers.

I intend to test my pump for pressure as soon as I pick up a testing gauge. If my pressures are off, will replace the pump assembly. Am leaning toward the Bosch as I trust them to make good stuff but am not certain that they make the right one. Some of these pumps say "all models" while others specify R code or with and without RFI. Mine I believe should be the R code as it is the 8th digit in the VIN of both Tahoe and Yukon. Which pump do I need? Would it matter if a Bosch had the RFI or is it just the wrong one for my truck?

I do wonder about electric connections, have checked all that I can find and put alittle dab of dielectric grease on them. I have not done the one on top of the gas tank which is fun to get at, should try that next. There seems to be something here related to damp weather and would not like to change a fuel pump if not needed. I read about plug wires and greasing the ends of them as well, mine are pretty new and will grease them as well.

Any ideas?

Thanks, sorry for the long thread.

Bill

[MT-2500]

When no start check for lose of fuel pressure or lo0s of spark to spark plugs.

Post back fuel pressure readings running down road and cold start and when no start.

[MT-2500]

The only good fuel pump is the Delphi OEM type fuel pump.

[777stickman]

Originally Posted by MT-2500

The only good fuel pump is the Delphi OEM type fuel pump.

Agreed. Make sure you provide your full VIN to get the right pump for your application.

Try this link for more affordable prices on the OEM pump.

http://www.gmpartsdirect.com/

[BillPete]

Finally got around to checking fuel pressure on this truck. It tests at about 63 pounds, should be adequate from what everyone says. Also tested the spark this time and spark is orange, not blue so not hot enough. Next question, what is the most likely culprit? Have heard everything from plug wires not making good contact or being inferior quality to ignition module and coil. The wires are pretty new and "standard brandname". I don't know if this stuff is bad or not but it is the same name of the cap and rotor that I bought. My thoughts are coil or ignition module with coil on the top of my list. I am going to apply some dielectric grease to ends of plug wires to test them and same to connections at coil, distributor and ignition module if I didn't already get those.

I also have my wifes 99 Yukon that is identical and can test a few parts back and forth. Had already done so with the fuel pump relay which made no difference.

What do you guys think? Thanks,

Bill

[MT-2500]

Proper testing.
A one time shot at fuel pressure is not a proper test.
Always check for lose of spark and fuel pressure at the time of no start.

A good code check may show problems to.

That airtex fuel pump is junk and may or may not be the problem.
But they have a high fail rate and are known not to have proper fuel presure.
Run a full fuel pressure test.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
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.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding 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 at least 75-85 or more.
And specson yours may be as high as 95-105 lbs.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[BillPete]

Some updates on this situation.

I have changed the cap and rotor twice, first with an aftermarket (Standard brandname), didn't trust it and bought an AC Delco.

Have also changed the coolant temp sensor to a new AC Delco. I thought this may have been the problem as when we checked the connector, greased it, the truck started immediately. We found the old one to be cracked and separating. Next day, back to the same old difficult cold starts.

The battery is new, the alternator has been checked OK. I swapped the coil and ignition module with my wife's Yukon, made no difference to mine but hers still starts and runs fine. I also swapped the fuel pump relay between the two vehicles, same story.

It really seems to have something to do with the coolant temp sensor circuit as it acts as if it's not quite getting enough fuel for a cold start. What else could be in that circuit? If I crank on it enough, I can get it to start after a few minutes and then it will run fine and start fine.

The fuel pressure reads 63/64 pounds and does not seem to leak down. I checked with the mechanic who put in my fuel pump and he said it's a Delphi, not that old either.

Thanks for any help. Am trying to solve this before I trade the truck in.

Bill

[j cAT]

the ECT is a good possibility especially with no codes..

swap out the ECT or before doing that measure resistance of the ect on both vehicles cold and see that the resistance is the same. check the connector to sensor


if the resistance is different the computer will not turn on the injectors long enongh to allow cold start..

[BillPete]

Originally Posted by j cAT

the ECT is a good possibility especially with no codes..

swap out the ECT or before doing that measure resistance of the ect on both vehicles cold and see that the resistance is the same. check the connector to sensor


if the resistance is different the computer will not turn on the injectors long enongh to allow cold start..

Isn't that the same as the coolant temperature sensor? I've changed it twice already, first with an aftermarket part, then with an AC Delco. The part itself must be OK but what else tells this thing to deliver enough fuel for a cold start?

Thanks,
Bill