2002 trailblazer wont start once warmed up

[chet]

02 TB LT 4.2 4wd 200,000+ miles starts just fine when cold but once it warms up i just get at most a pop. I get nothing if i just crank on the ignition, but if i put the gas pedal to the floor it gives the pop like it might start to start. I have to wait at least 30min and it will just start right back up. I changed out the plugs which where very wore out but did not fix the problem. I have put it on the android scan tool but nothing is coming up on it right now.

Its not over heating.
oil looks good
oil pressure looks good
antifreeze looks good
plugs just changed

Thanks for the help!

 

[IllogicTC]

Unless oil pressure is tested with an adapter fitting at the oil filter connection, it's either <12 PSI, or >=12PSI. The oil gauge on the 4.2 models is a lie. No, seriously, the PCM simulates movement on it.

When holding the pedal to the floor on these trucks when starting, it enters flood mode - it'll disable the fuel and just use the cranking to pull fresh air through the cylinders in case the engine is flooded. While we're on the subject of the throttle, when's the last time you did a throttle body cleaning?

Perhaps if you're having whacky warm weather suddenly like we're having, the winter blend gasoline is causing some part of this issue, but I don't know.

And when you say nothing comes up on the scan tool, do you mean nothing at all, or that it does talk to the PCM just fine and there's no error codes or anything?

I don't know any other questions to ask, I'm still learning the quirks of the fuel system myself. One of my guesses would be some injector problem or vapor lock (does that even occur on FI vehicles these days?). I cannot guarantee those are actual problem areas. Speaking of which, have you verified fuel pressure?

 

[djthumper]

02 TB LT 4.2 4wd 200,000+ miles starts just fine when cold but once it warms up i just get at most a pop. I get nothing if i just crank on the ignition, but if i put the gas pedal to the floor it gives the pop like it might start to start. I have to wait at least 30min and it will just start right back up. I changed out the plugs which where very wore out but did not fix the problem. I have put it on the android scan tool but nothing is coming up on it right now.

Its not over heating.
oil looks good
oil pressure looks good
antifreeze looks good
plugs just changed

Thanks for the help!

Do you have any trouble codes popping up? What maintenance have you done recently? What has changed recently?

 

[CaptainXL]

02 TB LT 4.2 4wd 200,000+ miles starts just fine when cold but once it warms up i just get at most a pop.

Sounds like too much fuel. As you described it will run fine when cold but will not run when warmed up. Disconnect the fuel pressure regulator vacuum hose and cap off the hole on the intake. See if that solves it.

The pop you are hearing is the fuel igniting due to pressing the gas pedal all the way down. This initiates the "clear flood" mode and stops the injectors thus leaning out the mixture resulting in a brief uncontrolled backfire.

Could also be a bad coolant temp sensor.

 

[Midnyteryder196]

* Subscribed * As Im having same issue with starting issues when truck is warmed up and its warm outside.

 

[CaptainXL]

This is a common problem not just on our platform and engine. The most probable cause is a bad coolant temp sensor. It's flooding the engine when doing a warm start as the pcm thinks its a cold start adding more fuel.

The Op stated that it tried to run when the pedal was depressed far enough to add more air thus causing a backfire. That's significant.

You need a scan tool to check coolant temps when doing a warm start. If the coolant temp sensor checks out I would lean towards a bad fuel pressure regulator. A bad diaphragm will cause the engine to suck in excess fuel and flood the intake resonator with fuel on shutdown. This will create a rich condition when attempting to restart the engine later.

As far as the op's situation goes it is pretty much overdue at 200,000 miles to get a new fuel pressure regulator. The fpr is for all intents and purposes suspect when mileage starts climbing past 130,000 miles and I would strongly consider it a preventative maintenance item which should be changed around that mileage, if not sooner...say 100,000. Like when the spark plugs are changed.

 

[Midnyteryder196]

This is a common problem not just on our platform and engine. The most probable cause is a bad coolant temp sensor. It's flooding the engine when doing a warm start as the pcm thinks its a cold start adding more fuel.

The Op stated that it tried to run when the pedal was depressed far enough to add more air thus causing a backfire. That's significant.

You need a scan tool to check coolant temps when doing a warm start.

Thanks Captain,
I replaced ect sensor today, along with the purge solenoid.
tb was cleaned about 1500 miles, also just a few miles (maybe 100) before tb was cleaned the t stat was replaced.. which started the issue.. had the battery unhooked to replace t stat, and since then hard starting when warm, but seems to happen all the time when temps are above freezing, and part times under freezing..

When its hard starting, it seems like if i keep trying to start, but flutter the gas pedal it will start.. seems to take anywhere from 5-10 times trying to start, but eventually it will..

temp reading when it happened tonight was probably 50-60 degrees ambient, with coolant being around 190 degrees..

 

[CaptainXL]

Sounds like you have done most of the troubleshooting already.

Next step will be to get a fuel pressure gauge and hook it up. See if there any movement on the gauge letting it sit over hours. If the fuel pressure bleeds off over time then you could have a leaking fpr or injectors.

 

[IllogicTC]

Leaky injectors. The reason it starts cool is because the fuel has had time to evaporate off. Check fuel pressure at the rail, and see if it bleeds off.

You could try cranking for 5 seconds with the pedal to the floor. This disables the injectors to clear flooding. Then let off the pedal, and try again and see if it starts right up or starts at least in fewer tries than what you have been having.

 

[Midnyteryder196]

Sounds like you have done most of the troubleshooting already.

Next step will be to get a fuel pressure gauge and hook it up. See if there any movement on the gauge letting it sit over hours. If the fuel pressure bleeds off over time then you could have a leaking fpr or injectors.

now that you mention it.. my fpr did look a lil wet around the edge... Never really thought of that, I had always thought it would be a sensor since the problems didnt start for me until i unhooked battery to replace the tstat...

 

[CaptainXL]

now that you mention it.. my fpr did look a lil wet around the edge... Never really thought of that, I had always thought it would be a sensor since the problems didnt start for me until i unhooked battery to replace the tstat...

If the fpr is wet then it is definitely bad. Regardless if it is the problem or not I would replace it first before continuing the troubleshooting. Then get back to us.

Also now would be a good time to replace the fuel filter if it has not been done within the last 30K or so.

 

[Midnyteryder196]

is the fpr one of the parts our 4.2 gets over with aftermarket parts? or do i need to stay with delco?

 

[CaptainXL]

is the fpr one of the parts our 4.2 gets over with aftermarket parts? or do i need to stay with delco?

As far as I know ACDelco is the preferred brand we like to use. Not saying you can't use another brand but you are probably going to find little price difference so I would just stick with what's proven best for us. Amazon usually has the best prices.

http://www.amazon.com/dp/B000C9NAWE/?tag=gmtnation-20

 

[IllogicTC]

is the fpr one of the parts our 4.2 gets over with aftermarket parts? or do i need to stay with delco?

I'm not sure that it does. It seems like electronics tend to anger it more.

For the Genuine GM / AC Delco Part: 88894176

They're looking about $90-100. Find an aftermarket equivalent to this part number if you'd like, but I don't know how the engine would react to it. Try searching the forums and see if anything crops up.

 

[CaptainXL]

I'm not sure that it does. It seems like electronics tend to anger it more.

Yes, mostly electronics parts. But at $63 plus free shipping this is pretty much a no brainer. The same ACDelco fpr I listed is selling for $80-$100 on eBay plus shipping.

 

[Midnyteryder196]

Thanks guys! Delco fpr ordered along with a filter.. will report back wen they are installed

 

[CaptainXL]

Thanks guys! Delco fpr ordered along with a filter.. will report back wen they are installed

After they are installed you still need to check fuel pressure and see if there is a leak somewhere. Could be a connection, fuel pump or injector as IllogicTC stated. Report back your static pressure readings.

 

[Harpo]

* Subscribed * As Im having same issue with starting issues when truck is warmed up and its warm outside.

Me to.
Typical if I'm stopping for fuel, then it won't start if you don't press the pedal to the floor. And this occurs in winter and last summer no matter if I drove for 30 min or 5 hours.
Would be interesting to follow this.

Fortunately I have a spare -05 engine to pick parts from,question is if fpr and injectors are the same as my -02.

Sorry, not trying to hijack the thread,just got exited. Don't know how I missed this thread.

 

[KNBlazer]

Unplug FPR vac line from resonator (blk box) point away from engine and crank, fuel shoots out, you'll have confirmation.... I recently replaced mine with an AcDelco unit, only problem I had was a mysterious fuel smell that I couldn't find.... finally with the truck idling, I found the source....