Q45 is sick, knocking and poor idle

[mbogart]

:help My 1990 Q just started knocking really bad one day while in stop and go traffic. I have repolaced the CAS as recommended by Scottsdale and put in new gas plus octane booost but the problem persisits. They also said it had given a code for bad knock sensors which i bouhgt but haven;t installed yet. It has 167,000 miles and I don't know if the chain guides have been replaced but it was running perfect and just sailed through our state emissions test and delivers consistent 22 mpg. A local shop said it had skippped a tooth on the timing chain and recommended areplacement engine. Now it's been sitting so long my wife and neighbors are getting irritable. Need to do something quick.

[DAEDALUS]

A local shop said it had skippped a tooth on the timing chain and recommended areplacement engine.

Did they check the base timing? Have you pulled the spark plugs yet? How old are they? They could be fouled up.

[mbogart]

spark plugs are new, I tried to set the new CAS in the same position as the old one but didn't check the timing, hadn't found this great resource yet and though i have the big tech manual it is still sketchy in many areas, or too cryptic to understand easily.

I had a crack in the rubber air intake some time earlier that i tried to patch so I'm thinking It may be running too lean if its getting more air than the air sensor is reading. It will run steady at cruise but sound like a machine gun when you push it hard. There was no lead up to this, no gradual deterioration of any kind it just started instantly under no particular load, althoug running slow on the freeway in arizona with the air on can be tough on everything.

I had worked under the plenum with help from a real mechanic a couple of years ago and replaced about 6 of the bigger hoses but didn't know about the hose kit at Scottsdale even though i bouhgt the hoses one at a time from there. The PCV hose shattered when i tried to move it a while ago and tiny pieces of that may have escaped down inside and could be contributing to the problem but it seems like they would burn up pretty fast.

[azskygod]

You really need to determine whether the knock is a result of preignition ping or something else. Where in Tempe are you located? I work around 44th Street & McDowell and could listen to it over lunch sometime if you're close. I know exactly what an engine that jumped time sounds like.

AZSKYGOD

[911/Q45]

Was that PCV hose replaced? A vacuum leak would cause your symptoms.

[mbogart]

Yes, hose was replaced with off the roll hose rather than the pre formed item from Infiniti, but yes, I guess a vacuum leak would cause a lean condition that could result in knocking, I'm not sure where all the sensors are or how they work together. I plan to replace the rest of the plenum hoses if it hasn't jumped a tooth on the timing gear. As I have read in other posts on this service, the leather is in such good shape and the interior and exterior are all above average so It will be hard to abandon this car. If it comes down to new chains and guides I will have to do most of it myself to make the money come out. I already got a new ABS controller and AC compressor both installed at sun devil auto just recently and those together cost more than the car is worth.

[DAEDALUS]

Check the base timing; you could be way too advanced. What service(s) did you do most recently before this happened? What brand are your plugs?

[mbogart]

the plugs are Bosch platinum. the most recent service was a new air filter and oil change. That was when the PCV hose shattered and the air horn cracked. Too much arizona heat it seems. I experimented with the full range of basic timing when installing the new CAS and there seemed to be no difference no matter where it was set, it seemed not to respond at all which could be because of the bad KS?? Scottsdale Infiniti reported a fault code for the KS as well as recommending the new CAS and wiring harness. Being green at this, i inspected the harness and saw no problem so i didn't bother to replace it.

[1992Q45A]

Get rid of those Boschs!!

You need the OEM recommended NGKs... Boschs have been reported as causing nothing but trouble.

Since you are in tempe (another AZ guy, how cool) anyway, you may want to have euro imports take a look at your car.. They have great techs, and provide great service at a fair price

[mbogart]

I hear you, i read several prior posts and lots of stuff about not using any plugs but NGK. There is very little help out there for those of us trying to save these magnificent old beasts so this service is fantactic and lots of us are in AZ it seems. I don't know where else you can get basic stuff like this and Ive googled this subject several times before coming across NICO by accident

[1992Q45A]

This is really it...

Once you join, you can never leave (evil laugh)

This is by far the most definitive collection of Q enthusiasts..

Those plugs have to go... NGKs arn't too expensive, $75 or so..

Wish I could say the same thing about Knock sensors, hopefully you won't have to do them.. although if you do, you will probably regain some lost performance..

I had mine done at euro imports

[90Q45blue]

Those plugs have to go... NGKs arn't too expensive, $75 or so..

$66 from Joe for the set.

Nick

[1992Q45A]

Even better!

[elwesso]

$55 from me!!!

If you search in the online mechanic, i posted a super easy way to check the timing..... Id like for someone else to try to make sure it works...

[Q451990]

When my guides failed, I had a very irregular idle and backfiring. I think I skipped two to three teeth though, because the car was still running, but I had some minor valve damage on one cylinder. I wouldn't rule out guides.

Heath

[mbogart]

Shouldn't that show up on a compression test? It seems that if one bank of cylinders has all the valves opening at the wrong time, there ought to be a difference in the compression readings.

[maxnix]

Only if the valves are bent. I think Q45tech said there is only a one tooth tolerance. Can't remember how many degrees, but I bet it is less than 4°.

[texasoil]

jumped timing chain will definitely show up on power balance test.

Will also show on compression test.

[maxnix]

True, there should be some bank to bank variation, but if it has already skipped, I wouldn't want to risk further damage with a compression test.

[Q45tech]

There are 36 teeth on cams so each tooth is 10 degrees. There are 18 teeth on crank so each tooth is 20 degrees.Two revolutions of the crank is just one revolution of the cams.

[azskygod]

Don't forget, for reference there's a video of my engine running on a slipped driver's side timing chain at ftp://69.26.192.114/MVI_0493.AVI.

AZSKYGOD

[maxnix]

That's a great post. Needs to go in the NICO archive. What a sad sound.

[texasoil]

a camshaft that 20 degrees (crank angle) late (0ne tooth on the cam sprocket) will result in an engine that barely runs--if at all. On my Maseratti quad cam hemi engine, the cams were individually adjustable in 0.5 degree increments (a combination of internal/external splines on drive sprocket), and 1.5 degree would make a real significant difference in idle.

[Q45tech]

In reality 20 degrees cam retard idles pretty badly until warm especially if only one is retarded and the CAS is not reset.This the timing [light is often a clue] as most slips occur on the driverside.

We had one where the exhaust cams were both retarded but the intake was ok and the CAS was reset to 15 degrees interesting to say the least. Idle a little shakey but WOT above 6,000 was powerful.......cruise with AC was also funky.

248 degrees and 8 degrees overlap at idle is pretty benign with HLA.......but when slipped and VVT on at 1500 the overlap goes from 28 to 48 degrees [lopey to say the least].