200 miles on the lower intake manifold gasket repair on my 2002 Blazer (199,400 miles). No coolant leaks, no oil consumption (three changes to clean up the coolant/oil). New rotor and cap. Compression good. Idle, acceleration, power are all strong and steady. The idle does not hunt or falter but it is not smooth. It's kinda grumbly. Rough but very steady.

I will check the vacuum but I normally associate vacuum leaks with other problems. Never touched the fuel injectors. Did a fuel pump at 100,000. What should I look at? One thing I have never done is motor mounts, never owned a truck long enough. Could that be it?

Thanks,

George

 

Is your misfire detection operational? SES light operational? Have you checked cam sensor retard (should be 0° ± 2°) Have you checked fuel pressure per sticky at the top of this forum - all 4 readings? These are the basics.

 

A shaky idle especially in gear is a pretty common thing. I've read it is an unbalanced motor design, (a cut-down 283?) but it seems to me that something like that would not be allowed onto the showroom floors by Marketing. I suspect the mounts or maybe something in the transmission or even the A/C. If you find out, post it!

 

Checked the engine computer and no codes.

Fuel rail pressure with priming cycle on = 62 psi

Fuel rail pressure just after priming cycle cut off = 55 psi

Fuel rail pressure after 10 min leak down interval = 55 psi

Is the lack of trouble codes sufficient to rule out a cam sensor retard fault or do I check that live with the code reader?

Thanks,

George

 

The list of causes for a rough idle are probably pretty universal but most engines have specific items that go bad routinely (like the lower intake manifold gaskets on this engine). Does anybody have any guidance on where I should start as this whole list would take quite some time:

Fuel pressure (just tested mine and its good).
Fuel filter (probably been 50k miles)
Injectors (I have never cleaned these)

Rotor (new AC Delco)
Distr cap (new AC Delco)
Ignition wires (probably have 80k miles, AC Delco)
Spark plugs (probably have 80k miles, checked the gaps at compr test, all looked good, AC Delco)
Coil(s)

PVC
IAC
MAF
EGR
O2 (replaced as they failed)
Throttle body
Idle speed

Thanks,

George

 

Nope cam sensor retard can be way off and not set a code - need to check it live with a capable scanner.

I already told you where to start. If you want me to help then please finish the tasks and we can go further. These are all basics that need to be verified before getting in deeper.

p.s. you still need to report dead ended fuel pressure and leakdown.

 

I will look and see if my scanner can read cam sensor retard

I did report leakdown and it passed as well as the pressure with the pump energized. The sticky that you sent me to suggests testing the output at the fuel filter if the readings at the fuel rail fail so that you can determine the source of the failure. I presume that this is what you mean by dead ended pressure. If not, please explain.

 

Unfortunately neither of my scanners can report cam sensor retard so I am at a dead end there.

Looking at my live data I see that long term fuel trim is -9.5 on both sides so the system is compensating for running too rich. I know that fuel trim can drift as an engine ages and that double digits is bad. Is a -10 LTFT an expected value for a 200,000 mile engine or should I chase the source of the rich mixture?

Thanks,

George

 

I'm glad you're working on this, George.

 

Try running some seafoam thru the fuel and vacuum systems and see if that'll help at all. Stuff works wonders. And only costs about 8 bucks a can at commie-mart. Also, your fuel trim readings sounds a little like you might have some faulty o2 sensors. Perhaps further testing there.