3800 V6 hot start issue

[04silverprix]

Okay, my wife's 2004 Grand Prix with the 3800 Series III V6 has developed an inconsistent hot start issue.

On occassion after the car has reached operating temperature it will become hard to start. It'll stumble and quit or stumble and barely start. Eventually after cranking one or two extra times, the car will start and run fine. Upon starting for the first time of the day, the car has no issues.

I am not getting a check engine light, so I cannot look for any trouble code.

I have the proper fuel pressure. The fuel filter has been replaced. I checked the engine coolant temp sensor (ECT) with an ohm meter and it registered 4,000-5,000 ohms at room temp (roughly 50-60 degrees). I went to an auto parts store and performed the same test on a new sensor at the counter and got the same ohm reading as the one on the car.

I don't think it has a fuel delivery issue and I still have not ruled out the ECT because I read a conflicting test that states the sensor should have an ohms reading of 7,000 to 8,000 ohms.

Has anyone else experienced a similar issue? I'd like to know what else to check. The car seems to run fine it just has an occassional starting issue after the engine has reached operating temperature. The car has just 64,000 miles and we've had no trouble with it.

Maybe I should check the battery cables. I don't think an analyzer can help until the light comes on and I can get a code.

[jmoore4294]

Try taking the throttle body off and cleaning it. Get rid of all that carbon build up.

[04silverprix]

You know I heard that elsewhere. I also heard something about cleaning the MAP sensor.

I guess it won't hurt. The car is driven in town most of the time, so there's likely plenty to clean off.

It would be a first for me if a simple solution as cleaning turns out to be the remedy to one of my car problems.

Thanks.

[04silverprix]

I misinterpreted something in my last post. I think the Mass Air Flow sensor can be cleaned, not the MAP sensor.

I will try to clean the throttle plate. The car has SFI instead of a TBI unit, but I think there's a throttle plate on the air plenum that can be cleaned.

I'll have to look further.

[jmoore4294]

I've got an 04 as well. There's 4 bolts on the throttle body and the whole thing comes right off.

Cleaning your MAF and Throttle Body: 2004 - 2008 Grand Prixs

[cerick08GP]

I was thinking maybe the throttle body myself, but logically it would start crappy most of the time if it was. By all means clean it, all GP owns should every year or so. Moving on.
IMHO, it is most likely your battery. Or battery related item. Check the voltage on your battery just after a long drive it should be like 12.6-12.8 volts. And then check it after sitting all night it still should be in the upper 12s. While you’re at it check all the wires from the battery-alternator-starter, including the grounding points. Also while idling your car should be putting out about 13.5-14volts, it is best to check this when the car is “hot” with a good amount of load on it (turn on your defroster and blower fan). Failing alternator diodes tend to work a bit better cool.

If this doesn’t pan out, look for a leaking fuel injector. Take that pressure gauge, and see how long the system holds pressure at key off.

[04silverprix]

The battery was replaced in the fall, but that doesn't mean it can't be a battery/battery cable issue. I plan on looking that over when cleaning the throttle body assembly.

Last week I replaced the fuel filter and we checked the fuel pressure and it seemed to read normal. If I had a bad injector, wouldn't the car run lousy or idle rough? I pour a bottle of injector cleaner in the tank every month in my late model drivers, but it wouldn't hurt to make this pressure check you suggest.

Thanks for the sound advice.

[cerick08GP]

Well, you are correct. A leaking injector “should” cause other drivability issues. With these kinds of things you never can tell for sure, you would be amazed how many ppl come on this site looking for help and are totally disconnected from how there car performs until it doesn’t work anymore. Regardless, a car with your symptoms “usually” has fuel delivery issues or charging system issues. That being said, it could be any of a half a dozen other components. My motto in helping ppl is to go for the low hanging fruit first. (stuff that is easy and cheap to fix). Anyway, I have one more bit of informed advice. After hang out here a while one notices a definite pattern of what fails on a GP, and one item that does fail regularly is the crank position sensor (CPS). “Normally” when it starts to fail it manifests itself in other ways, but in your case did look to it next.

[04silverprix]

Thank you. Absolutely go for the low hanging fruit. Another suggestion I received is the next time our GP acts up, turn the ignition on and off/wait twice and then attempt to start the car. If it starts, it could be a faulty fuel pressure regulator.

I still want to make sure those other components are okay before I replace any parts. Patience is often the best tool in the cabinet.

[sportred04]

its not your battery or cables. clean the throttle body and itll fix the problem. do it every spring and you wont have a problem.

[cerick08GP]

Thank you. Absolutely go for the low hanging fruit. Another suggestion I received is the next time our GP acts up, turn the ignition on and off/wait twice and then attempt to start the car. If it starts, it could be a faulty fuel pressure regulator.

I still want to make sure those other components are okay before I replace any parts. Patience is often the best tool in the cabinet.

Yup, I didn’t forget about the fuel pressure regulator. They do fail fairly often on high mileage GPs, however your car doesn’t have one. And besides you seemed pretty confined you have good fuel pressure.

[04silverprix]

You're correct cerick08GP. I looked for a fuel pressure regulator on an online parts site and there isn't one listed. I also consulted my Haynes manual and it states the same.

So I will just check the other issues discussed on this thread and see what I find. I just need to take the time to tinker around and see if I can find something. I just don't want to assume and start replacing parts.

My wife went errand running with it after work this evening and the car didn't do anything wrong, so it is an intermittent issue.

[Sporto]

I've had this same intermittent issue for about a year now. For me it most occurred on the 2nd start-up of the day, usually going out at lunch or leaving work for the day and the temps outside are rather warm. However the issue is happening more often we're in February in Northern Indiana (just got 5 more inches of snow last night).
I will attempt the TB cleaning soon.
Oh, I replaced all 3 coil packs, didn't help.

[04silverprix]

Yeah sporto I have the same issue with the weather as well. I plan on checking and cleaning before moving on to any parts.

I have a question for cerik08GP regarding the crank sensor. If the crank sensor on our car was acting up, would the check engine light kick on? I would think if a sensor were defective, it would trigger the light and kick out a code.

I found a very useful how-to on this site about how to replace the crank sensor. I must say, this web site is very useful and I'm impressed about the number of people who covet these cars.

[cerick08GP]

I have a question for cerik08GP regarding the crank sensor. If the crank sensor on our car was acting up, would the check engine light kick on? I would think if a sensor were defective, it would trigger the light and kick out a code.

Well, believe it or not a CEL usually doesn’t come with a CPS failure that is what makes them a PITA to trouble shoot. They apparently have no self checking feature to throw a direct code, there is no way that I’m aware of to test them, and they are not exactly easy to get to.

“Most of the time” when these start to go bad on GPs ppl get a random traction control light and/or their tach will go all wacky intermittently. But engine restart problems (like you are having), engines cutting out, or engines just plain dying are possible.

[Terry102]

Mine does the same, its a leaky injector...now finding what one is the trick =)

[04silverprix]

If I have a leaky injector, are there repair kits for them, or would it be best to just replace the injector?

Maybe I'll luck out and the throttle plate cleaning will be the remedy.

[cerick08GP]

Mine does the same, its a leaky injector...now finding what one is the trick =)

Yup, I suggested he check that way back in this post

[sportred04]

just clean the damn TB and itll be fixed.

[04silverprix]

Hi guys, well it's been about a month and my wife's '04 Grand Prix has been normal.

What I did was remove the air intake hose off the throttle body and doused it good with a can of carburetor cleaner. It was dirtier than Larry Flint, so it needed a good cleansing anyway.

I started the car and it smoked some and I drove it about a mile and it seemed to drive fine. After that I told my wife to pay attention to how it started and she reported no problems. I had no trouble either when I drove it a little.

Now this has me thinking. My 2002 Silverado with a 5.3L V8 has 150,000 miles and I have not cleaned the throttle plate opening. I have not had any trouble, but I think I will remove the hose and give it a cleaning. Maybe the trucks have more cubic centimeters of space opposed to the tight quarters of these cars. I don't know, but I'm glad our problem was solved with a can of carb cleaner.

Thanks for your input.