big flat spot and popping

[Anonymous]

The V is experiencing a big flat spot when under acceleration. i can be fine then, if power is applied quickly (as in overtaking etc) it revs for a short time then hits a flat spot and the power will not resume until the revs drop, which is then followed by a large pop from the exhaust. it doesnt do it at a set rev range it can be anything from 3k to 6k. so practically the whole rev range is affected. it doesnt do it all the time either. i can change up a gear and it will rev through fine. its like it gets stuck at a certain rev limit and wont rev no higher but it changes all the time. its a similar feeling to hitting the rev limiter in a diesel car.

from what i have read on here it looks like it could be a possible lamba sensor causing this problem??

please help because its driving me mad!!!


jack

 

[taipan]

Not mechanically minded but I had a similar symptons in my old RX8. Changed the ignition leads and coils and voila probelm solved.

If it is dodgy coils this is a common problem with the Vees. Do a search and you'll find loadsa info.

 

[Kevred]

The fuel filter tends to get forgotten about due to it being time consuming and diffiult to change , when you do fit a new one its worth cutting the old one in half to see how much crap is in it

 

[Anonymous]

i thought possibly coils but surely if it was the coils i would notice the flat spot all the time not just under heavy acceleration. fuel filter is a maybe where is it located?

 

[Spike]

i thought possibly coils but surely if it was the coils i would notice the flat spot all the time not just under heavy acceleration. fuel filter is a maybe where is it located?

how many miles? 20k + needs a fuel filter, its a pain to change but for about ten quid!!!!

 

[Anonymous]

any help on this?

 

[Jamesv6]

Although I would tend to go with SPIKE on this one.

 

[Spike]

any help on this?

What sort of help are you after? advice, or mechanical help?
there are many knowledgeable members on here who are only too willing to help, see if there is anyone closer to you than nottm, where i am, if no one comes forward pm me and if i get in your area i will come and have a look, but use the forum, we wont bite.
any takers children?
alternatively pay for my gas and i'll come over if you are stuck, but try the filter first.
and again, how many miles on the car? spike.

 

[k1ano]

Could be ecu going into limp mode for some reason, though I would expect the engine light to be on, but I would also try an obd diagnostic check for stored fault codes ... there is also a simpler fault code check you can do via the dash but you will have to check the knowledge base as I can't remember off the top of my head...

Martin

 

[Spike]

Could be ecu going into limp mode for some reason, though I would expect the engine light to be on, but I would also try an obd diagnostic check for stored fault codes ... there is also a simpler fault code check you can do via the dash but you will have to check the knowledge base as I can't remember off the top of my head...

Martin

FULLY AGREE....... :approve:
i can help with a scanner, but it will not register fuel pressure or flow in obd codes, or even man specific! i have built a rig to test fuel pressure at the tank whilst isolated from the ecu, but you still have to lift the carpet and hatch.

 

[WONGY]

I had similar to this on mine - it turned out to be a knackered fuel pump

Reason is the car sat at a dealer with low fuel so the fuel pump rusted to bits!

They found it per Spike's suggestion e..g OBD showed nothing, so had to use a clip to measure the fuel pressure which nosedived under load

I think the handbook says always have 2 gallons minimum in the tank to make sure the pump is submerged

 

[Anonymous]

i do have a scanner will bang that on it later see if it shows anything and will keep you posted!

 

[k1ano]

Heres is a section 'clipped' from the knowledge base article which indicates that fuel flow can be read by the dash diagnostics - I assume there must be a pressure sensor in the fuel rail rather than assuming the fuel pump is working optimally, if so, this should give you an indication as to whether your fuel pump/pressure is within tollerance ...

Reading Engine Diagnotic Codes

<snip>
Starting Diagnostic Mode

With the igition off press and keep hold of the button at the end of the wiper stalk and then turn the ignition on. All the dashboard warning lights will come on and the speedo and rev counter will go through a predefined 'dancing' sequence. Once in this diagnostic mode, pressing the stalk button will sequence you through the various bits of diagnostic information on the digital read-out.

Diagnostic Information

The following details will be displayed as you cycle through using the wiper stalk button.

All the lights lit (shows if you have a failed LED).
The amount of fuel left in the tank in liters.
Fuel flow (the engine has to be running. This is in liters per hour
Stored faults

t - an injection fault has been detected for a minimum of 4 seconds.
J - a fault has been noted on the fuel gauge. It must have disconnected for longer than 100 seconds. The resistance from the fuel tank sensor needs to be between 5 and 350 Ohms.
d - an injection signal fault has been detected.
h - an oil level sensor fault has been detected. Resistance from the sensor should be between 6 and 20 Ohms. Any reading over 20Ohms is an open cicuit anything under 3 is a short circuit.

NB: If no faults are logged then dashes will be displayed. Also note that no other faults are displayed.

Clearing And Ending Diagnostic Mode

To clear faults - press the reset button to clear the logged faults. To exit diagnostic mode - turn the engine off or move the key to the off position.
<snip>

 

[Anonymous]

i will have a look at this also when i get home! k1ano thank you for that

top man! [smilie=icon_cheers.gif]

 

[Spike]

Heres is a section 'clipped' from the knowledge base article which indicates that fuel flow can be read by the dash diagnostics - I assume there must be a pressure sensor in the fuel rail rather than assuming the fuel pump is working optimally, if so, this should give you an indication as to whether your fuel pump/pressure is within tollerance ...
<snip>

THERE IS NO CONNECTION BETWEEN FUEL PUMP AND ECU!
sorry but i had to shout, yes there is data displayed on the dash but its calculated from rpm and injection time, nothing else! there are no fuel pressure sensors or flow sensors or even any clever gismo's. the ecu detects engine running and holds the pump relay energised, thats it. the pump as we all know is in the tank, also in the tank is the fuel pressure regulator which is a mechanical unit that will control the pressure even at minimal flow. there is not even a return from the engine as the return is just a tee piece mounted after the filter.
this all means the engine or ecu does not see any flow restriction or pressure drop, so long as there is fuel there the engine will run, abeit tick over. put your foot down under these conditions and at best you will feel a flat spot at worst it will die, a fault code will log if driven for long enough via the lambda, showing out of range. this is because under load the motor is running piss weak, at this point you get the lambda or lambdas changed and find out its just the same, you've just got less money in your wallet.
i do agree with wongy with the fuel pumps falling to bits, but you can test for this by over pressurising the system temporararily and reading the pressure, should run at 4bar (ph1) or 3.5 (ph2) but you should see 6 bar if you clip the return. if yo do not get a raised pressure after clipping the return go for the pump.
if its a ph2 a worthwhile mod whilst replacing the pump is up the pressure to ph1 spec, definately a performance increase with midrange.
STILL NO MENTION OF MILEAGE!
if you need more info on how to do this by all means ring, 07889 153352, I HATE TYPING, spike.

 

[Anonymous]

41351 miles spike

 

[k1ano]

Yes no need to shout LOL ...

Just had a read of a Bosch ME 7.4 technical manual and yes there is no electronic fuel pressure or temperature sensor so calculation must be based on the 'assumption' the pump is working optimally.

Out of interest I copy a few notable points which I had read about previously - they may help people a bit (I add them here so I can put them in the knowledge base later) ...

Diagnostoc light operation (explains why the engine light goes off after a coil failure)

The LED located on the control panel is controlled by the ECU. On a multiplexed vehicle, this information is broadcast on the CAN network.
For L4 and ifL5 depollution, the engine diagnostic LED is used to inform the driver that the regulatory pollutant emissions level has been exceeded.
Operating mode of the LED for L4 and ifL5 depollution:

•ignition off:−the LED is extinguished.
•ignition on, engine off:−the LED is illuminated.
•engine running:−no fault:the LED extinguishes.

Presence of a major permanent fault with LED permanently illuminated:

•the LED will remain illuminated to warn the driver that the regulatory emissions level has been exceeded,
•it will extinguish when this fault successfully passes 3 diagnostic sequences.

Presence of a major permanent fault with LED flashing:

•the LED will flash after misfires to warn the driver (risk of damaging the catalytic converter),
•the LED will stop flashing when the misfires have disappeared.

Note: For the ME7.4.4 injection system, all faults affecting the motorised throttle or the pedal sensor cause the diagnostic LED to illuminate immediately.

For K' depollution, the diagnostic LED is used when there is a risk of damaging the engine.
The LED illuminates when the fault appears and extinguishes when the fault switches to temporary.

Automatic clearing of 'some' fault codes

Faults can be erased without using a diagnostic tool. The ECU can automatically erase a temporary fault from its memory if it does not reappear within 40 warming up cycles.
A "warming up cycle" is a vehicle operating period which is sufficient to allow the engine temperature to increase by at least 22°C from when the engine was started and reach a minimum temperature of 70°C.

Programming the pedal position sensor (to avoid poor running or loss of power)

The programming procedure consists of programming:

•The idle position of the pedal sensor in order to recognise the idle position of the accelerator pedal,
•The maximum position of the pedal sensor in order to recognise the full load position of the accelerator pedal.

The accelerator pedal position sensor programming procedure should be performed after:
•replacing the ECU,
•replacing the accelerator pedal position sensor,
•repairing the accelerator pedal position sensor after a fault is detected,
•downloading the ECU,
•telecoding the ECU.

Pedal position sensor programming procedure
•accelerator pedal at rest,
•switch on the ignition,
•press the accelerator pedal down fully,
•release the accelerator pedal,
•start the engine without accelerating.

Important: If this programming procedure is not performed, the ECU will not be able to precisely recognise:

•the idle position of the pedal sensor in relation to the idle position of the accelerator pedal,
•the full load position of the pedal sensor, where this information is required to control torque requests from the driver.

 

[Spike]

THATS ALL FRENCH TO ME! usefull info though.

 

[k1ano]

I used to be a software engineer though so have always had a fascinating with EFI systems and tinkering about with them :ihatepcs: bring back carburetors, points and distributors I say, you know where you are with them :rofl:

Keep us posted Jack on your findings too as your issues seem extreme especially if no engine warning light is being lit. You could try the throttle re-programming above - as this is a simple thing to eliminate (barring faults with the pedal/throttle units).

Martin

 

[Anonymous]

i have removed the carpet from the back and opened the hatch. how do i now remove the fuel pump to see if it is buggered or not??