G50: Help with a diagnosis

[Teach45]

I love the site and check back often. Thanks to everybody that contributes and makes it such a useful tool.

I got my 94QT back in Feb 06 and it has been flawless thus far. I am having my firts problem an its intermittant nature has me baffled. I have researched on the site but maybe you can hepme out. Since Febuary I have put about 15K on with hardly a hiccup, just a new alternator in early march.

Here goes the problem. Every few days the car can be a little sluggish. Engine smooth but as if it is lacking enough fuel. This goes away and all is well for days. No buzzing sound from the pump at all. I put in a can of BG44k mabe it improved but because this is so intermittant I can't really tell.

The car has 130k and I don't knw that the fuel ump was replaced but it may have because I found a printout of the wiring diagram for the pump in the trunk when I bought the car and the previous 2 owners had been very good about mantenance. (can't contact them now to ask)

When this is happening the Q will stall when I pull into a parking spot and when I rev sghtly if I come off the edal it aso stals.

Ony other clue is that this first happened after a three hour drve in hard rain.

Thanks

[maxnix]

Welcome to our club with your first post.

Have you checked the MAF connector? Check the wiring also for corrosion. There was a running change to the final 1995 configuration during the 1994 model year.

It is customary for new ownvers to exchange all fluids and filters immediately after purchase unless there is documentaion suggesting it was done correctly in the immediate past. This is a little more critical on a 1994 and before t model as teh PS fluid is shared with the HICAS system.

Total miles?

[Q45tech]

Weird intermittents as you describe can often be traced to sometjing in the FPCU.

Often the easiest solution is to just swap things like FPCU and MAF, that cannot throw ecu codes if they function at all even BADLY.

The problem is used parts may be bad because of their years of use and create similar or different problems.

Short of continuously recording min max fuel pressure gauge or min max MAF voltage monitor diagnosis is difficult. Even MAF voltage doesn't tell you everything because it could just be off [from perfect] by 20% [ a few 0.1 volts] and cause a lean misfire under cruise conditions.

For regular customers we just swap the part and wait a week to charge the customers credit card until they inform use the problem really went away...........or ask them to come back and try something else and pull out our test part. 9 out of 10 times we guess correctly because we have had 10 years of experience with the 90-95Q.

I have a personal spare for every electronic module and sensor that I frequently use, however most problems tend to be bad connections or bad solder joints from excessive current as rotary or impulse parts degrade.

After 10-15 years many relays have pitted contacts which can cause problems [starter] [Fans] [Fuel Pumps] [Compressor clutches] [ABS] {TCS}

All one can do is find someone in US that works on SO MANY that they are clairvoyant especially after a few hours of testing.

[Teach45]

Thanks for the quick reply. So you are more likely thinking MAF or FPCU than the pump necessarily.

Can the pum be going and manifst this intermitantly. Should I lt the tank run low and see if it is worse.

I think I have an extra fpcu and maf on hand will try thse next week,

Can the pum go without the buzz?

[Teach45]

130K thousand miles total

[maxnix]

1.) Can the pum be going and manifst this intermitantly. Should I lt the tank run low and see if it is worse.

2.) Can the pum go without the buzz?

1.) Not usually. There is just more drag and it turns slower while pulling more current in an attempt to maintain fuel pressure. Why Q45tech recommended measuring fuel pressure.

Knowledgeable owners never let the tank go below ¼ in normal operation since the return line and the gas in the tank serve to cool the pump and the fuel system.

2.) Rare, but it has happened.
Modified by maxnix at 8:09 AM 1/18/2007

[Teach45]

I actualy never do and use bg44k every month or so just thought letting the tank drop would be a way of showing if the pump was at fault

[3Q Jay]

careful about using the bg44k all the time. it will attack the soft metals (rod bearings). accepted practise is to run a tank of the 44k just before oil and filter change (refuel near empty before changing oil). yeah i know--violates the 1/4 tank rule--the one exception i can think of.

[Q45tech]

What chemical component in BG44k will attack the bearings..???.......2 solvent chemicals which naturally occur in gasoline and the amine/amide detergent are the sole components.

Ring wear is usually the limiting factor in engines.

With 90 DAY oil changes you never have bearing problems.

[qship96]

I always see a spike in lead # in my oil analysis after running bg44k , normally 3-4 ppm lead readings,spiking to 11-15 ppm after using bg44k. something in bg44k is causing increaded bearing wear-why recommended to use in last tank of gas before oil change......

[Q45tech]

But the BG44k would need to get into oil which means your rings are already excessively worn or it somehow breaks down the ring tension.

That is the rub.............more old worn cars get additives to try to crutch them on.

Are you using the required/suggested MOA [111] oil additive at every change................the Zinc protects against extreme wear which may be misssing in modern oils. ""the zinc compounds react with the metal to prevent scuffing, particularly between cylinder bores and piston rings...."

Modern oils have reduced zinc since if you burn oil the zinc reduces cat efficiency..............how much zinc is show by your oil analysis?

All in all every additive including the use of gasoline has it's up and down sides...............Not knowing what you are doing can easily cause extra wear and damage.

All in all one is better to keep fuel additive usage to the minimum. Unfortunately the bulk of US fuels won't allow this.

[qship96]

qtech- I doubt my rings are worn,as oil always changed at less than 90 days since brand new- mobil 1 for first 100,000 miles,Redline since then also at 90 day intervals- currently at 185,800 burns no oil ever- Redline is soo rich with zinc and moly{over 1400ppm zinc,700ppm moly} and a group 5 ester based synthetic designed for max. protection.Insoluables results from my analysis suggest low blowby,no fuel dilution,and low silicon{dirt}

[Black stallion]

What about any increase in sludge?

[qship96]

I dont understand your question? clarify please!

[Black stallion]

An increase in sludge due to the properties of syn oil - because it doesn't burn like conv oil

[qship96]

synthetic oil is LESS prone to sludge than conventional oil,not more prone!

[Q45tech]

Sludge is from not changing oil frequently enough so that it gets very viscous [all the light fractions have boiled away] like tar/asphalt after its antisludge additives are used up.

It can happen to synthetics also just takes longer since their boiling/flash point is higher by 100-150F.