Hard start and rough shut down

[Mike534x]

It's been about a year now since I last posted when we still had our 02 Envoy. Recently my parents bought an 04 Trailblazer Ext for my brother to drive to school and its having some minor issue we can't seem to figure out. Currently its sitting at 143k miles and has the I6.

Here's what we've done to it so far;

Replaced the Autolite plugs with Iridiums
Replaced the Variable Valve Timing Solenoid (threw a code)
Cleaned the throttle body
Oil change

What needs to be done;

Front + Rear Sway bar links
Front + Rear diff fluid
Transfer Case fluid
Fuel Filter

Here's what we're trying to figure out, its mostly starting up the truck it feels a bit rough, kind of like it isn't getting what it needs to start,its worse when its cold, its hard to explain unless you feel/hear it. Next is the shut down, it feels very abrupt, the best way to describe it is like once you turn the key to the off position it kind of sputters and vibrates the truck enough that you feel it through the steering wheel and seat. The idle is very smooth so I'm just wondering if a bad fuel filter is to blame or if this is something else entirely.

 

[KNBlazer]

I would either use a top tier gas and or a bottle of Techron Fuel treatment.... also the mileage, and age, I would probably replace motor mounts...

 

[Mike534x]

Poured in a bottle and half of Slick 50 last week, with no noticeable difference. I was wondering if the motor mounts were bad but I thought when they go you can feel the entire truck vibrating with the engine?

 

[IllogicTC]

Poured in a bottle and half of Slick 50 last week, with no noticeable difference. I was wondering if the motor mounts were bad but I thought when they go you can feel the entire truck vibrating with the engine?

Not necessarily. They generally deteriorate and give poorer performance over time, rather than full-out complete failure.

 

[gmcman]

When did the "rough" symptoms first appear? Before you changed what part(s) and/or after you changed what part(s)?

Open the hood and put in gear, rev slightly and observe motor tilt, in forward and reverse. How much? Vid?

 

[Texan]

I am probably behind times, but did you pour the Slick 50 in the crankcase or fuel tank?
I was not aware that Slick 50 made a injector cleaner.

 

[Mike534x]

Not necessarily. They generally deteriorate and give poorer performance over time, rather than full-out complete failure.

Oh ok. I wasn't aware they usually go out over time. I thought it was usually at once or when the other fails.

When did the "rough" symptoms first appear? Before you changed what part(s) and/or after you changed what part(s)?

Open the hood and put in gear, rev slightly and observe motor tilt, in forward and reverse. How much? Vid?

The truck had the symptoms when we bought it. The rough idle was partially fixed once we cleaned the TB, we pulled the plugs and found Autolite Iridium plugs already installed but we swapped them out for Delco 41-103's which solved the idle issue. The only thing left is to figure out why the truck seems to have a slight hesitation to start and to figure out that rough shut down. The engine doesn't really seem to tilt too much in forward or reverse. I'll have to get a vid posted tomorrow when I'm home.

On a unrelated note, the rear HVAC blower stopped working even though it was fine a few days ago, so that looks like it'll be a project on its own in the spring.

I am probably behind times, but did you pour the Slick 50 in the crankcase or fuel tank?
I was not aware that Slick 50 made a injector cleaner.

They make a fuel system treatment. My next option was to try running seafoam through the engine to see if its just the amount of carbon build attributing to the problems.

 

[triz]

Check the motor mounts with someone. When mine started to go out it happened pretty much the way you described it. You might just not have noticed when they started going out.

 

[Sparky]

Check the fuel pressure regulator. If the diaphragm inside cracks it can leak down pressure when the vehicle is off, so it starts harder. The FPR on the 3800 series engine was notorious for that happening and causing hard starts. If it is bad enough you can smell gas in the vacuum line when you pull it.

 

[Mike534x]

Check the motor mounts with someone. When mine started to go out it happened pretty much the way you described it. You might just not have noticed when they started going out.

We did check but they didn't appear to be shot, but we're going to replace them anyway just so its one less thing to work on and since it seems to be common to have them go out around this mileage, we may as well do it.

Check the fuel pressure regulator. If the diaphragm inside cracks it can leak down pressure when the vehicle is off, so it starts harder. The FPR on the 3800 series engine was notorious for that happening and causing hard starts. If it is bad enough you can smell gas in the vacuum line when you pull it.

We didn't even think of checking that. Just by chance, know the truck doesn't have a PVC valve, but does the PVC hose running from the resonator to the engine do anything? When we went in to change the plugs/clean the TB there was some oil build up on the outside part of the hose that connects to the engine so I'm just wondering if that is something I need to keep an eye on.

 

[Mounce]

Make sure you use ACDelco motor mounts, other brands aren't made to the same quality and don't handle the vibrations right. And I haven't seen much about the hose but I assume it just keeps the vapors outta the crankcase and prevents it from building pressure inside.

 

[Texan]

You are correct about the I6, it does not have a PCV valve. But it does have
a crankcase vent system. The hose from the resonator to the valve cover is the
filtered fresh air inlet to the crankcase. Over at the intake manifold there is a hose
in the center of it that is the vacuum source for the vent system.

 

[Mike534x]

Make sure you use ACDelco motor mounts, other brands aren't made to the same quality and don't handle the vibrations right. And I haven't seen much about the hose but I assume it just keeps the vapors outta the crankcase and prevents it from building pressure inside.

This is odd. Its been cold the past few days and the shut down has actually gotten smoother, we managed to get a few extra hands to see if we can get a look at the engine mounts and they still looked like they were in decent shape but then again I don't have the new ones to compare for an old vs new side by side shot.

The start up is still hard. We're hoping it warms up a tad bit to get a better look at the fuel pressure regulator as recommended by Sparky, which makes me wonder if this is the source of the start issue. I'm going to try posting the video tomorrow of a cold start to show what I mean. Maybe its normal for the way it sounds but it feels like there is a slight delay from the time the key is turned to when the engine actually cranks.

 

[Texan]

I think that the 04 TB has a fuel filter outside of the tank, underneath the rear driver side seat (outside)
with a Schrader valve for checking the pressure. I would check the pressure. Should be around
50 +/- PSI and not leak down when turned off.

 

[Klambro]

It's your motor mounts...they don't have to look bad to be bad. What you are describing was happening to my 03TB as well. I purchased the GM mounts and attempted to replace. I was able to get the passenger side fairly easily, but the driver's side was too difficult and I have yet to replace it (I will get to it). Even just replacing the one, the start up and shut down are completely different now. No shudder at all. Good luck

 

[KNBlazer]

It's your motor mounts...they don't have to look bad to be bad. What you are describing was happening to my 03TB as well. I purchased the GM mounts and attempted to replace. I was able to get the passenger side fairly easily, but the driver's side was too difficult and I have yet to replace it (I will get to it). Even just replacing the one, the start up and shut down are completely different now. No shudder at all. Good luck

Disconnect neg batt cable, Remove your alternator, remove both upper and lower nuts, raise engine, and remove bolts from engine side motor mount brackets....