Tucson John68

My truck is a 2002 5.3L 1500, Z71, with about 93,000 miles. It has never had many problems. About a week ago in the morning (normal 70 degree night, no rain) letting it sit for 10 hours, the engine was very hard to start. The cranking noise was different. It was not the starter relay clicking like a dead battery. It was more like a labored, higher pitch noise. When cranking for more than 2-3 seconds, it felt and sounded like one or two cylinders were trying to fire, but not all of them. When releasing the key, sometimes for 2-3 seconds one or two cylinders would slowly fire, then the engine would stop. If I crank for 5 seconds or more, it seems like several more cylinders would start firing (not all eight) and will keep running slowly (without touching the gas pedal). The engine will lope about at very low idle, obviously without all eight firing. I can push the gas pedal and the engine will gradually increase its speed and it seems like all eight cylinders will fire at 3,000 rpm and above. Then after 5 seconds, releasing the gas pedal will improve idle, but it is still obvious that maybe only six cylinders will be firing. If I hold it at 3,000 rpm for about 10 seconds, then all eight will fire and then everything is normal. If I don’t hold it at 3,000 rpm, the lack of all cylinders firing will cause a misfire code to be set. After I get the engine running normally, it starts up with one crank with no issues. It will run as if it were new. After work (85 degrees weather), letting it sit for eight hours, a similar condition occurs, but a lot easier to start than first ting in the morning.

I replaced the battery. No change of course. On Saturday, I brought the truck to my mechanic (ASE master mechanic, 50 years old, lifetime experienced). The truck was hot and of course, started right up. After a lot of discussion and eventually noticing that the fuel pressure did drop when in the bay for a while, replaced the entire fuel pump assembly (in the gas tank) and the fuel filter. Since the fuel pump goes out at about 90,000 miles anyway, so I told him to change it. With high hopes this morning (45 degrees and dry), I cranked the engine, with no change.
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Since this is Sunday, I have to wait until Monday to drop off the truck for more work. So, any of you have any ideas as to what is going on?
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Since the cranking noise sounds different, can it be the starter and will that cause the horrible temporary idle?
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Could it be electrical? If so, why would it start just fine when hot and immediately after getting it to run normal?
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Is there anything else in the fuel system that could cause this condition?
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What gets me is that once it is started and idling normally, it runs like it was still new. Then I can turn if off and it starts just fine for hours.

Thank you for your ideas!

Mille Racer 69

have you checked your spark plugs?
I would change them IIWY.
Then run a bottle of marvel mystery oil in your gas tank and then take
a bottle of seaforam and put 1/2 of the seafoam in through your vacuum pump
via the PCV valve hose is what I use and then take the other 1/2 of the bottle and
put it in your crankcase where you put your oil about 100 miles before you change
your oil to get all the crap outa your oil and engine. I use marvel mystery oil with
every fillup, but I suppose you could use it with every other fillup.
you can get MMO and SF for cheap at walmart or for a little more at any other auto store
for a little more.

Do not pour all the seafoam in through the vacuum line all at once. do it slowly or truck will die
but you just restart it and continue. there are youtube viseos on this.

kevinkpk

I thought of water in the gas, but since (I assume) tank drained the pump was replaced. Seafoam is a good idea, but I'd think if it where a problem with the possible water in the tank, the lines would have been cleared.

charledl

I have the same exact problem with my 2006 4.8. Mechanic thought it was the crank position sensor and replaced it; did not solve the problem. I would appreciate any advice also.

Mille Racer 69

Seafoam and marvel put in your gas tank not only will take out all of the moisture that is from all the ethonal in gas there days, but it will also clean your injectors and other vital componants like sludge or carbon buildup on top of your valves.

loosebearing

Sounds like fuel pressure regulator.. located under the air plenum ect. If it is leaking will have a clean spot on intake. Sounds like something flooding engine .What misfire code are you getting? p0300... po306 po 174 ect.

MDTAHOE

Pull the vac line off the fuel pressure reguator after it has been sitting. It is right on top of the fuel rail in plain sight. I am sure you will find raw gas in it. If so replace it it will take less than ten min.

Remove the engine sight shield.
Relieve the fuel system pressure. Refer to Fuel Pressure Relief Procedure.
Disconnect the fuel pressure regulator vacuum line.
Clean any dirt from the fuel pressure regulator retainer and the surrounding area.
Remove the fuel pressure regulator retainer (8).
Remove the fuel pressure regulator (9).
Ensure none of the following parts are still in the fuel rail:
Backup ring (10)
Regulator seal O-ring (11)
Regulator filter (12)
Regulator seal O-ring (13)
INSTALLATION PROCEDURE
Insure that the NEW fuel pressure regulator retainer is the correct one.
The tabs (1) are used on the straight vacuum port retainer (2), and the E85 straight vacuum port retainer (3).
The angle vacuum port retainer (4) has no tabs.
Install the following parts onto the fuel pressure regulator (9), if necessary:
Backup ring (10)
Regulator seal O-ring (11)
Regulator filter (12)
Regulator seal O-ring (13)
Lubricate the fuel pressure regulator O-rings (11,13) with clean engine oil.
Install the fuel pressure regulator (9).
IMPORTANT: Whenever the fuel pressure regulator is removed from the fuel rail, NEW O-rings and NEW retaining clips should be used on reinstallation.



Install the NEW fuel pressure regulator retainer (8).
Connect the fuel pressure regulator vacuum line.
Tighten the fuel fill cap.
Inspect for leaks.
10.1. Turn ON the ignition with the engine OFF, for 2 seconds .
10.2. Turn OFF the ignition for 10 seconds .
10.3. Turn ON the ignition, with the engine OFF.
10.4. Inspect for fuel leaks.

Install the engine sight shield

Tucson John68

Funny thing is that the morning after the fuel pump was replaced, there was no change...it did not start easily. The morning after that (day 2) and the rest of the day, it started on the first crank with absolutely no issues. Now day 3 in the morning, same problem with starting, but the rest of day just fine.

I'm not sure about problems with the gasoline or intake since the problem is only with starting and not while running. It runs very smooth once all cylinders are firing. Also, once the engine starts the first time, all other starts are perfect. The new problem came about all of a sudden and has persisted. As for the engine codes, I did not read them myself. My mechanic told me they were just misfire codes. I know they were set when not all cylinders were firing (obviously).

I bought a fuel pressure regulator and plan on replacing it the next time I have a problem starting the truck. Note that I never did see any gas in the vacuum hose connected to the fuel pressure regulator. It smells a little bit like gas in the vacuum hose, but defintely no liquid gas present. I checked maybe five times over the course of the past three days.

Thanks for all the ideas and I'll keep this post updated, if the problem is every permanently solved.

Tucson John68

OK...this morning (day four and 50 degree and dry) the truck would not start easily, so I was prepared with my tools and new fuel pressure regulator. I depressurized the fuel tank and the fuel system by opening the fuel cap, removing the fuel pump relay, and cranking the engine. Per the instructions above, I replaced the fuel pressure regulator then primed the fuel system. Very easy replacement. Cranked it once and it fired right up like it was new. Give me about a week of consistent starts before I claim that the problem is fixed. So yes, it appears that the fuel pressure regulator was causing the problem. Maybe the fuel pump was also an issue, but it definitey was not the complete solution.

A couple of things to note is that when I removed the old fuel pressure regulator, about one cup of unpressurized fuel spilled out. So, watch out if you have a hot engine! I had a rag handy for such an event. The new fuel pressure regulator went in with a little bit of extra effort since the o-rings were a little tight. Finally, the typical way to determine if the fuel pressure regulator is bad is there will be liquid gasoline present in the vacuum hose. Mine never had that, thus complicating the diagnosis of a bad fuel pressure regulator.

I'll give one final post after a week to say if the problem is completely solved. Thank you to everyone for the help!

MDTAHOE

If you were smelling gas in the hose at all it was leaking. When the truck has a extended crank due to the fuel pump it does not run bad when it starts. Your ran bad because the cylinders were over loaded with fuel especially the ones closes to the vac port