G50 : Hesitation, Bucking, Jerking, Loss of Power, Choked Acceleration ...

[lino]

My car has had this problem for months now.

Here are some of the symptoms:

• When I try to accelerate, I have to really go easy on the gas to get the car to move and accelerate. Most of the time, I will ease off the gas, because the car will feel choked like it is flooded with gas, or starved of gas, or as if there is something electronic cutting the power. I have to do this "ease-on-ease-off" to gain acceleration. It really is like a balancing act. I find myself having to use the hazard lights sometimes, as the car will almost not leave the line at a traffic light and people will beep their horns.

• There is hesitation.

• There is bucking and jerking.

• There is a big loss of power. Sometimes the power comes back and the car takes off like a bat out of hell! Most of the time, it feels like 6 cylinders are not working.

• Sometimes I'll floor the car and the engine revs high, but the car goes nowhere. It only continues going at the same speed it was going before flooring the car. So I let off the gas.

• The shifting of the transmission is affected by this problem. Sometimes the car doesn't want to shift and the hesitation, bucking and jerking is present. When the car shifts, the car accelerates, but not as it should. The hesitation is still present. I tried driving the car is "3" and that doesn't help.

• Fuel economy is down considerably.

• This happens when taking off from traffic lights, driving at slow speeds and highway speeds.

• It is very rare that I see the RPM gauge go over 3000-4000.

• The car struggles to go up a hill, if I for example make a slow down make a turn, step on the gas and try to go up a hill.

Not too long ago I have:

• Had the Fuel Injection System cleaned professionally • Put a can of BG44K and 2 bottles of Red Line Fuel System Cleaner

• Cleaned the Throttle Body

• Clean the Mass Air Flow Sensor with Electrical Spray (q45.org)

• Replaced the Air Filter with an OEM part

• Replaced the Fuel Filter with an OEM part

• Replaced the Spark Plugs with NGK PFR-5B11

In the last week or so:

• The ECU gives me code 55. That's the only code I ever got from this car. I just did the test last week.

• I have replaced the MAF with a used one. I was told the car it came from had 78k on it. I can't be 100% certain that is "a known good MAF". It does look very clean.

• I checked the knock sensors and fuel injectors:



• I also tested the TPS:

[elwesso]

Ive been working with Lino quite a bit to get this figured out.

Im just wondering if anyone thinks the small difference in TPS voltage matters. Im thinking its trivial mainly because we cant be sure the voltage we're seeing the same thing the ECU is seeing, however, lets assume at idle the ECU sees .32 volts instead of the .44 volts it wants to have. What kind of differece would that make?

I certainly do not think the TPS has much to do with the issue.

[burijon]

Fuel pump or fuel pump controller issues? You can look at the controller and see if has any burns on it.

[lino]

There are no signs of burn marks whatsoever.

Here are some pics. (Sorry for the poor quality):











I had a hard time trying to take a clear picture of my FPCU, so I used a pic of a unit that is not mine. The numbers that I have added are the numbers that are on my unit.

[Q451990]

There are two common failure modes for the FPCU. One where the connector (or leads on the PCB inside feeding it) are burnt. The other is internal. I would open the FPCU and look for signs of overheating on the four transistor-like parts. They are actually screwed to the aluminum housing of the FPCU for heat disappation. Then again, it can be bad and not show any visible signs of being toasted... then you get into the "substitute a known good unit" testing.

Heath

[elwesso]

Now just ground out the fuel pump and see what that does.

[kidstayridintheq45]

have you had anyone look at your exhaust system? does it smell funny when you r driving....try checking out your catlaytic converters they might be clogged this could make your car do aLL OF WHAT U SAID AND CHECK FOR ANY VACUME LEAKS/ PCV VAULE

[sdkhalsa]

I had similar symptoms on my 94' Q. Originally thought it to be fuel pump, but after tee'ing in a gauge while operating, found that this was not the case. The problem was a bad knock sensor. Using a consult set-up on my laptop, I observed that the timing sharply retarded during these acceleration problems where normally it goes into significantly into the advance range. I might add that I had run the car with a vacuum gauge previously to check leaks, but there were no signs of any.

[maxnix]

Sounds like a good diagnostic routine, but wouldn't detect the melting then reforming of cooling solder on the FPCU board.

[lino]

Now just ground out the fuel pump and see what that does.

Just did that, drove approximately 30 feet and the car died. I tried to restart and nothing. I had to push the car back to the driveway. I put the connector back and nothing. The fuel pump does not come on anymore .

[goody90q45]

Just did that..... I put the connector back and nothing. The fuel pump does not come on anymore

I put in a newish FPCU today and took this pic while I was there. Is the pin with the alligator clip on it the one you grounded (lower left pin with the connector's clip up)? If you used an alligator clip you have to flatten or grind down the tip to fet it in deep enough to get good contact with the pin.

[maxnix]

So in summary, you have neither replaced the fuel pump nor inspected the circuit board of the FPCU?

[lino]

So in summary, you have neither replaced the fuel pump nor inspected the circuit board of the FPCU?

No, I have not yet. I don't have spares so that would mean that I would have to buy them. I see people buying these parts used, and I recall reading posts by q45tech where he doesn't recommend used ones. I really don't want to buy parts that I might not need. If I need them, then I have will.

I haven't taken out the FPCU yet. I can do that now, since it's the weekend.

***Update***I tried taking out the FPCU and was unsuccessful. I was able to remove the rear seats and part of the rear shelf, but that's it.
Modified by lino at 11:36 PM 3/16/2007

[lino]

I just did a test on the fuel pump. Here are my results:





I changed the results in this post, due to different results after more testing.
Modified by lino at 8:07 PM 3/17/2007

[lino]

I put in a newish FPCU today and took this pic while I was there. Is the pin with the alligator clip on it the one you grounded (lower left pin with the connector's clip up)? If you used an alligator clip you have to flatten or grind down the tip to fet it in deep enough to get good contact with the pin.

Thanks for the pic Mike I did not use an alligator clip. I just used wire and it was in there good.

[goody90q45]

***Update***I tried taking out the FPCU and was unsuccessful. I was able to remove the rear seats and part of the rear shelf, but that's it.

The shelf should pop right up. Put both hands and arms up to your shoulders between the shelf and the deck and pry up. When the last clip comes loose you'll know, the shelf will move forward. You've removed the 3rd brake light by twisting it CW and unplugging it?

If you're only removing the FPCU though you don't have to remove the deck. It just needs to be pryed up a few inches, just enough to get a short screwdriver in at the edge to remove some tarry insulation and then a small ratchet to remove the two bolts.

The FPCU is held in by only two 10mm bolts and they are all the way forward next to the thick rubber pad under the seat back. They are hard to find, unless your FPCU has been removed before, since they were covered in a tarry insulation sheet at the factory. Look at the pic and draw a straight line from the two phillips screws forward. You'll have to remove the insulation covering them with a flat tip screwdriver first. Next remove the two bolts and the FPCU will drop down and you can remove it through the trunk.

[maxnix]

***Update***I tried taking out the FPCU and was unsuccessful. I was able to remove the rear seats and part of the rear shelf, but that's it.

Read Tangaloras immaculate posts. All is revealed.

[Q45tech]

Sometimes pictures work better:http://www.picotech.com/auto/g...m.png

Note ~~8500 rpm and 6 amperes

"Typical roller vane type automotive fuel pumps (running loaded) draw between three and six amps at 5,000 to 6,000 rpms (approximately) when they are new. They are designed to have a useful life expectancy that will usually take them just beyond the warranty period. "

http://www.asashop.org/autoinc...h.htm

Every vehicle has fuel pump failures just the when varies.

Ampere numbers for Q45 pumps:zer...53062

[lino]

So I did some more tests and here are the results:









B

C

D


Modified by lino at 12:54 PM 3/18/2007

[elwesso]

I think the next step is to figure out somehow if the relay is being triggered. Im not exactly sure how we could jump the fuel pump relay to force it on... I always get confused by how the relays work..

zerothread?id=144058http://forums.nicoc ... ?id=144059

see how those links treat you.

[lino]

I just found a spare fuel pump relay and swapped it. That made no difference either.

[maxnix]

Well, it seems like you need a (preferably new) fuel pump to see if the FPCU will power it. Good chance the old one fried the FPCU anyway, so why don't you inspect it per TAngalora's posts? If you have a fried terminal, all is explained.

[Q45tech]

You could substitute an electric fan motor or just a very high wattage 2 ohm resistor for the fuel pump and check the FPCU system.

WE know a good pump draws 3-7 amperes.

Always remember ocassionally we need to replace the pump and the FPCU TOGETHER just to get the system to run .

Standard proceedure at dealers replace BOTH immediately!

[elwesso]

Tech... I talked to lino on the phone and he said that the relay is not coming on when it should. As we know, the fuel pump relay makes a decent click when you turn the car on and then clicks off when the fuel pump is done priming...

The fact that the relay is [seemingly] not coming on? I guess another choice would be to take the fuel pump out, unhook the leads from the fuel pump and then test it to see if 12 volts is getting to the pump. There is power going to the relay and the ground seems to be good too?

honestly, im gonna be pretty upset if this whole bucking/jerking problem turns out to be related to a fuel pump because we've spent a LOT of time trying to figure out this stupid thing for it to be a damn fuel pump. it could at least be something a lot more fun to figure out then a fuel pump!!!

Tech, when you guys get in Q with FRIED fuel pumps that take out the modules, does it do roughly the same thing....?

[lino]

I thought I'd mention that I made some changes to an earlier post. I added some more tests. Now if I can only figure out how to do the next 2 tests

[maxnix]

Inspecting your fuel pump control unit board may tell you a lot.

[elwesso]

Basically what your doing is seeing if the RELAY works... You apply 12 volts to pin 1 and 2 (using a battery and a couple wires) and then you test continuity between the 2 terminals...

Honestly, Id skip the relay test and go to the FPCU test. The FPCU test is a bit more complicated... All your doing with that test is testing wether all 3 "speed" settings work properly.

[elwesso]

In all reality, it might be easier to take the FPCU out and see if the common solder joint is bad... If its OK, then youll need to take the fuel pump out and see if its getting 12 volts TO THE PUMP.

Here is my recommended course of action... If you'd like to continue playing around with things and testing stuff, thats all good with me and I'll help you do it, however I think it would be very who of you to just go ahead and get a new fuel pump and a known good used FPCU, replace both and see what happens... If you dont have record of the fuel pump being replaced, at 150k+ its served its time. Hell, even if it was repalced at 100k its not uncommon for them to fail.

I think its time to commence surgery... We can take stuff apart and test things in other ways that will make everyones life so much simpler... First step is to take the fuel pump out of the tank. Once we have the fuel pump out of the trank, we can see if theres voltage getting to the pump AND we can test the pump outside the car to see if it works...

[lino]

Inspecting your fuel pump control unit board may tell you a lot.

I finally got the fuel pump control unit out! I have the unit here next to me with both plates off and I can't see anything that looks burnt or wrong with it.














Modified by lino at 8:19 PM 3/18/2007

[lino]

Fuel pump is out.