Q45 acceleration problems?

[hockalougie]

I'm down in Texas and I own a 1991 Q45 with 86k. The car is currently driving on it's third motor (chain guides, of course) and the motor is estimated to have 15-20k. I did complete chain job and plenum hose job. I replaced one O2 sensor. And the MAF connection sparkles.Now here's my problem:The car is perfectly smooth, quiet and powerful...when in park. Once you put it in gear, it's okay until you accelerate. At anywhere from 1800 rpm to 2700 rpm while accelerating, the steering wheel shakes and the car vibrates enough to make inside pieces rattle. It's definetly more a vibration like from a massage chair than anything else.From 3000-4800, it's beautiful.Then, when you get to around 5000 with it floored, as when passing on a farm road, all power deceases, for about a second, then the transmission hits the next gear, and the car throws you into the seat as if it had 500hp.I know this is really complex, but it's definetly not a one time thing. It's been doing for 1000 miles now, and it only does the vibration when the engine is hot, but the loss of power is at any temperature.I am completely befuddled on what this could be, unless possibly the knock sensors. Can anyone help?Also- I've heard other Q's, and my cams rattle unusually loud. They were newer Q's (94-96) and I remember when replacing the engine in mine, the block numbers were in the low 1200's, while the original motor was more around 20k.

If it weren't for this site, that beautiful car would be in the Gulf of Mexico by now.

[911/Q45]

An hours worth of Consult testing at a dealer would be money well spent.

[downtempo]

I'm not the most knowledgable here, but it sounds like an injector problem. I have similar probs. with my '91 @ 93K. Maybe have them ohmed.

[hockalougie]

Actually that doesn't sound like a bad idea...I remember when I had the plenum off they were looking not so great, so maybe a replacement is in order?

[maxnix]

Fuel pressures? Any loud hum from behind the rear seat? New fuel filter?

Did you replace the camshaft timing chain tensionsers? Inspect oil pump and chain? Any old guide pieces missing?

[Jesda]

Everything Brian said above, and try this:http://www.q45.org/ohminjectors.html

[Q451990]

I'm down in Texas and I own a 1991 Q45 with 86k. The car is currently driving on it's third motor (chain guides, of course) and the motor is estimated to have 15-20k.

Are you saying that the car itself has 86K and the motor failed twice already? Typical guide failures happen at about 110-120K, although I've seen them as early as 77K. I assume the new motor got the updated guides?

It's a small world - one of my good friends lives in Tomball. Actually outside of Tomball, but I'm pretty familiar with the area.

I agree with the idea of it being an injector issue or fuel pressure problem. As 911/Q45 said, a Consult test at the dealership would be an excellent idea. See if they can do a PowerBalance test and give you the print-out and post the results here. You might also invest in a fuel pressure gauge and a hose long enough to run it out to tape to the windshield. Then you can check the pressure to be sure that it's OK.

Also, you mentioned that you had the Plenum off... what did you do while you were in there and how long ago was this? Also, you said that the injectors didn't look too hot while you were under there - what looked wrong with them? I don't think knock sensors are your issue.

Also, you mentioned your cams rattling... do you mean a lifter tap, or more of a fluttering rattling sound?

Good luck!

Heath

[hockalougie]

The car has a new fuel filter, all new timing chain tensioners and oil chain tensioners w/ the new oil pump change. The first motor actually failed because of lack of oil changes ( I estimate maybe every 10k?) but I bought the car with a bad motor so I'd have something to do.The first motor had a bad rattle, the egr was bad, and after we replaced it, the chain guide broke completely and seized the motor. It was estimated to have 30-40k (Sent from Japan)The new motor we planned to take no chances on, every part available except the chain itself was replaced for the timing chains. Under the plenum, water and emission hoses were all replaced. This was all at 82k.

Definetly there is a very loud hum from the fuel pump. It makes an erratic hissing noise when the tank is full, but when it's around a quarter, just loud humming. The fuel injectors looked as if they possibly leaked fuel...sure enough, 3k after putting the motor in, you smell gas every time you pop the hood.

With the cam rattle, you don't hear it when the engine is cold. Drive for 10 miles, and theres like a "clunk" with the fluttering. I know the fluttering is sometimes expected, but this is too loud.

I'll definetly look into fuel pressure and ohming.

[911/Q45]

Have the short hoses that connect the different injector system parts been replaced? These are the most likely cause of fuel leaking under the plenum, as they dry out and shrink.

[hockalougie]

ahh, no those have not been replaced. As I said, the only things under the plenum we replaced were emissions hoses and coolant hoses. Oh and those little intake gaskets.

[Q45tech]

Fuel hoses survive about 10 years because the gasoline junk eventually eats them up inside and tiny pieces flake off and lodge in injector screens and back to the tank where they are hopefully captured by the two gasoline filters.

All it takes is a few refinery short cuts to really damage the OLD hoses.

If the car makes it 10 years 150k, all the under plenum rubber should be replaced in mass.............sure it adds $300 [injector o rings, fuel hoses, all hoses instead of the obvious leakers [coolant pcv, etc] to a normal knock sensor/coolant hose job] but pay the labor ONCE every 100-150k.

Same with knock sensors and harness..............$1300-$1500 for everything is less than a penny per mile every 130k [average].

But those pennies do add up to 15 cents per mile for averaged out M&R.

8 cents for the first 100k [underwarranty], then 15 cents, then maybe 19 cents in the FINAL 200k-300k range...........~~14-15 cents for 300,000 miles with no accidents................$40-45,000 roughly what new MSRP was.

Obviously with NICO, doityourself and discounts you can save 10-30%.......not counting your TIME...........very few including myself find it economical to do every repair or maintenance function [not enough tools or test equipment] or skills or just old and tired like me [tire work, wheel work, serious parts replacement where $40 [discounted] an hour is cheap compared to my spending 3-4 times as long and no home lift.....or hurting my back.

Barter your car repairs...........find something you can do for a small expert independent shop.............electrican, plumber, accountant, lawyer, cut the grass, fix a roof leak............think what skill sets you might have that they need........at work or at their home.

Next month my 90 Q will be 15 years old [born on date] by then 275,000 miles by end of month...........now my tag advalorum tax is only $35 per year and insurance is only $500.

[hockalougie]

I've been doing my research on this site, and basically from what I can tell, I need to start replacing my fuel system from the fuel pump forward...and no, I really don't see the point of doing an Infiniti Consult...why would I want to spend $300-$400 for somebody to tell me my car is broken when I already know that?

Since the fuel pump has been bad for about 4k, I would figure the FPCU would start to go bad, but I haven't had any of the symptoms. I have humming, vibrations, loss of power, and leaking fuel under the plenum...and I basically know what all I have to do to fix each problem.

Also though, I figured out my fuel injectors are leaking inside the motor because the car has alot of trouble starting when it sits for twelve hours or more. So that means the gas is rinsing the oil off the cylinder walls causing loss of compression, therefore no go.

Also...my "Brake pads worn" sensor has been on for a couple hundred miles...thats the first job. Anyone have a link on instructions, and how do I reset the sensor? I hope I don't have to go to Infiniti...they want money...something I don't have.

By the way....I'm only seventeen, I make $6.25 an hour at the local Target...and even though my car has millions of mechanical problems, it's cosmetically perfect.