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Hard starting/engine misfires upon heavy acceleration
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superfizzo
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PostPosted: Sat Aug 06, 2011 9:50 pm    Post subject:  Hard starting/engine misfires upon heavy acceleration Reply with quote

I have been experiencing a couple of problems with my 2003 Impala 3.8L LS for just about ten months steady now. The car is coming up on 100000 miles. I tried replacing fuel filter, spark plugs, air filter, and the catalytic converter was changed 50,000 miles ago. I wanted to get your guys ideas about what could be the culprit and hopefully someone has had this problem before and can help me out before I get into serious overhaul mode. The good news is that it hasn't seemed to get any worse but it is still quite a nuissance.
I'll go more in detail to the problems that I am experiencing. On start-up the car will turn over just fine sometimes, other times it turns over and then dies quickly with a screeching noise. If I crank it again it usually starts up easily. Also, to note, the car will start up fine every time when I apply gas while cranking over. It has ran just fine after started until just 3 days ago when the engine died while I was waiting to get out of a parking garage. I am thinking more and more that it must be a fuel problem.
the acceleration issue happens any time I get on it and put the pedal to the floor. It will make a slipping/misfiring sound and doesn't have nearly the power it did when new.
Any ideas would be extremely helpful. It's been a great car for me and I need to get at least a few more years out of it.
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topgun
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PostPosted: Sat Aug 06, 2011 10:48 pm    Post subject:  hard starting. Reply with quote

If you think it might be fuel related connect a fuel pressure gauge to system. You'll have to look up what the pressure readings should be at idle and certain RPM's.
If spark related, could be coil pack getting weak. Ignition module. Ignition wires possible but don't think so with these symptoms.
Cool

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superfizzo
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PostPosted: Sun Aug 07, 2011 10:09 pm    Post subject:   Reply with quote

I'll give it a try with checking the fuel pressure and see if that's insightful at all. Any insight on how to do it on this vehicle? I'm assuming that it doesn't have a schraeder valve?
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IffyG
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PostPosted: Sun Aug 07, 2011 10:45 pm    Post subject:   Reply with quote

There is a schrader valve right on the fuel rail. Take the engine over off and take a look, it should be pretty easy to find.

I'd also look into your IAC (since you can get it running if you give it gas it might be stuck shut). I'd also disconnect the MAF and see what happens since it's easy to rule out the MAF as the problem.

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superfizzo
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PostPosted: Sun Aug 07, 2011 11:17 pm    Post subject:   Reply with quote

Thanks iffy. Anything I should be looking for in disconnecting the MAF? How can I tell if it is bad or not?
Anyway to check the IAC or should I just get a new one and replace it?
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PostPosted: Sun Aug 07, 2011 11:24 pm    Post subject:   Reply with quote

To test the MAF, all you need to do is unplug it. This causes the PCM to run on a different set of tables. If that car runs better with the MAF disconnected, it is contributing to the problem, if the car runs just the same, the MAF is not part of the problem. Since it takes all of 15 seconds and a quick test drive, it's an easy test to do.

For the IAC, you can take it out of the throttle body and see how gummed up with carbon deposits it is. I cleaned mine up with some MAF cleaner since I had it handy and put it back in.

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superfizzo
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PostPosted: Tue Aug 09, 2011 12:11 am    Post subject:   Reply with quote

Thanks again for the help. I tried both of the suggestions you made with some promising results.
I took off the IAC and sprayed some MAF cleaner in it. It seemed like the valve didn't want to move easily at all. I removed the screw and spring, cleaned them, and then reinstalled and saw some improvement in the engine starting. It is sometimes hard to diagnose because the engine picks and chooses when it starts up fine to begin with but I didn't have any hesitation for the first 5 times starting the car but it started to creep back again. I found a IAC from rock auto for $25 so I went ahead and ordered one.
I then checked on the MAF by unplugging it. The car, once again, would start up perfect every time with the sensor unplugged and hesitated on start up when I plugged it back in. Is there an option to effectively clean the MAF or am I better off shelling out the $100 plus for a new one?
I picked up a fuel pressure tester from harbor freight today but I haven't checked the pressure yet because I have no idea what the reading should be to even diagnose if mine is in acceptable range or not. Any Idea on where I could find what the fuel pressure should be at?
Thanks for any help
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IffyG
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PostPosted: Tue Aug 09, 2011 11:15 am    Post subject:   Reply with quote

Get a can of CRC MAF cleaner and carefully spray down the wires in the MAF. It's not guaranteed to work, but it's worth a shot before spending money on a new MAF.

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superfizzo
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PostPosted: Tue Aug 16, 2011 8:34 pm    Post subject:   Reply with quote

after cleaning maf and replacing EGR and IAC (it was cheap so why not), I ordered up a FPR in hopes that will appease the issues.

After cleaning the MAF and IAC it seems to have made a difference in the performance of the car under driving conditions. Still have the issue of hard starting. I'll update if it is fixed with a new FPR.
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shengang1203
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PostPosted: Tue Aug 16, 2011 9:05 pm    Post subject:   Reply with quote

Your car is 3.4 or 3.8? Mine is 3.4 and I could not break loose the Hex bolt

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Gems
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PostPosted: Wed Aug 17, 2011 2:21 pm    Post subject:   Reply with quote

If you do all of the above and continue to have hard starting issues then maybe your fuel pump is starting to go on you... Fuel pressure test should give you a clue, but I don't know what the correct pressure should be either...

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shengang1203
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PostPosted: Wed Aug 17, 2011 2:32 pm    Post subject:   Reply with quote

Gems wrote:
If you do all of the above and continue to have hard starting issues then maybe your fuel pump is starting to go on you... Fuel pressure test should give you a clue, but I don't know what the correct pressure should be either...


For my 2002, 3.4L, the range for fuel pressure would be around 52~59 psi. My test showed the value fo 52 psi (Key ON engine OFF, not cranking). I think that indicates the fuel pump is good. But does it tell anything about the FPR?

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PostPosted: Wed Aug 17, 2011 7:29 pm    Post subject:   Reply with quote

It's a 3.8L. Still waiting on the new FPR I got at amazon for just over $30 for a delphi. Great price on it compared to anywhere else so I figured I'd give it a go.

Interesting development. I've noticed if I let the engine idle for a while with the MAF disconnected, then plug the MAF back in the car will start great for a while. This problem is so intermittent it's been hard to pinpoint. I will probably end up getting a new MAF as well. Oh well why not replace all the sensors at 100k right?

I'll check the fuel pressure later and update.

UPDATE:
Checked the fuel pressure. I scored a 49 on it. A little low but I don't do enough mechanic work to know if that is the cause of my problem. Maybe someone with more knowledge could chime in.
Also, since the fuel pump is a $200 and 4 hour job, I won't be doing it until the summer months are gone either way so if the FPR or MAF does the trick, I'll let you guys know.
My car just hit 100,000 miles and I'm falling in love with it again. Cleaning up the throttle body and MAF sensor has given it some extra oomph and I did a full engine degreasing and gave it a good wax. Looks pretty good for a 8 year old car if you ask me. I have a nice sound system in it and am planning on riding it out until it dies so any extra parts that I end up with due to misdiagnosis can only help extend the time before they become the problem!
I figure what's the need in getting a new car when you have a great running car already paid for and taken care of? The only reasons why I would go newer can be taken care of by putting in an aftermarket head unit.
I am officially rambling here. I guess that's what staying up til 2am and going to work at 6am out in the heat can do to you. The sun done fried my brain.
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Frank3
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PostPosted: Sat Sep 24, 2011 10:15 pm    Post subject:   Reply with quote

superfizzo wrote:
It's a 3.8L. Still waiting on the new FPR I got at amazon for just over $30 for a delphi. Great price on it compared to anywhere else so I figured I'd give it a go.

Interesting development. I've noticed if I let the engine idle for a while with the MAF disconnected, then plug the MAF back in the car will start great for a while. This problem is so intermittent it's been hard to pinpoint. I will probably end up getting a new MAF as well. Oh well why not replace all the sensors at 100k right?

I'll check the fuel pressure later and update.

UPDATE:
Checked the fuel pressure. I scored a 49 on it. A little low but I don't do enough mechanic work to know if that is the cause of my problem. Maybe someone with more knowledge could chime in.
Also, since the fuel pump is a $200 and 4 hour job, I won't be doing it until the summer months are gone either way so if the FPR or MAF does the trick, I'll let you guys know.
My car just hit 100,000 miles and I'm falling in love with it again. Cleaning up the throttle body and MAF sensor has given it some extra oomph and I did a full engine degreasing and gave it a good wax. Looks pretty good for a 8 year old car if you ask me. I have a nice sound system in it and am planning on riding it out until it dies so any extra parts that I end up with due to misdiagnosis can only help extend the time before they become the problem!
I figure what's the need in getting a new car when you have a great running car already paid for and taken care of? The only reasons why I would go newer can be taken care of by putting in an aftermarket head unit.
I am officially rambling here. I guess that's what staying up til 2am and going to work at 6am out in the heat can do to you. The sun done fried my brain.


I put this on another thread in the forum.

Finally found the manual, getting to the right page for Fuel System Diagnosis was another story - page 6-890. Skipping some of the points that require a Tech3 tool to turn on the fuel pump. The procedure also stated to turn the key off, turn off all accessories. Connect a fuel pressure gauge to the fuel rail. Without a tech3, turn the key to ON - Do NOT start the engine. Repeat the key on several times to fully pressurize the rail so you read the highest pressure . The pressure on the gauge should read - 52-59 PSI. The fuel pump usually stops after turning the key to on (no engine running) after a second or two. When the fuel pump finally stops after the fuel pressure maximum pressure is reached and the pressure stabilizes, watch the pressure gauge to make sure the pressure does not drop more than 5 psi in 1 minute. Next with the engine NOT running , relieve the pressure in the rail so it drops to 10 PSI. Monitor the fuel pressure now for 5 minutes, it should not drop more than 2 psi in this time. The rest of the procedure requires a vacuum pump, a scan tool and specialized valves to shut off and isolate different parts of the fuel system. Luckily I found my problem and my brothers before we had to get any deeper into this. On my impala, the fuel pressure would not reach the specified high pressure when the system was pressurized AND would drop to zero on fuel pump shut-off.
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PostPosted: Sun Sep 25, 2011 12:53 pm    Post subject:   Reply with quote

The fuel pump is a 30 minute job tops. There is an acess right behind where the seats fold down.
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