DB9 Misfiring tried cleaning throttle bodies code p1797 HELP

DB9 Misfiring tried cleaning throttle bodies code p1797 HELP

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x15jq

Original Poster:

32 posts

125 months

Tuesday 29th September 2009
quotequote all
Hi all. I read the tutorial by Rick last week to clean the throttle bodies because I have been having a hesitating feeling on my 2006 db9 and rough idle mostly occurring in top gear from 1000-2500 rpm. I found the throttle bodies full of oily residue along with the intake pipes. After disconnecting the plugs and replugging on the throttles, I noticed the car was not running right. I disconnected the battery and all seems well for now. I was able to pull code p1797 and reset the engine light after it stalled out.

The car has 56000 miles I do not see any misfire codes.

Any ideas? Was I supposed to disconnect battery prior to removing throttle body connections?


Thank you in advance!!

rick-derby-

1,105 posts

137 months

Tuesday 29th September 2009
quotequote all
x15jq said:
Hi all. I read the tutorial by Rick last week to clean the throttle bodies because I have been having a hesitating feeling on my 2006 db9 and rough idle mostly occurring in top gear from 1000-2500 rpm. I found the throttle bodies full of oily residue along with the intake pipes. After disconnecting the plugs and replugging on the throttles, I noticed the car was not running right. I disconnected the battery and all seems well for now. I was able to pull code p1797 and reset the engine light after it stalled out.

The car has 56000 miles I do not see any misfire codes.

Any ideas? Was I supposed to disconnect battery prior to removing throttle body connections?


Thank you in advance!!
The systems adapt not only to driving style but also the sensors fitted, I presume if the throttle bodies had quite a build up then they would not be fully closing, so from a tech point of view, before you cleaned them they could have a value of say 1.2 volts closed, then you clean them and they return to the fully closed position reading 0.97 volts, as the system is expecting the first value, so re-adaptation can take a few trips(a trip is classed as from cold to a full warm up) The code p1797 is a communication area (can bus) the modules on the car use this system as a network, A battery reset can help with quite a few module related problems, without the benefit of the dealer diagnostic equipment to carry out the resets etc, The battery reset is the next best option and then letting the car tick over for 5 minutes before a run of mixed roads from cruising to accelerating and decelerating so revised values can be learnt,

Disconnecting the battery before removing the connections should not be necessary, just make sure the ignition is off,

We have now added throttle body cleaning to every service as again this seems to be a regular complaint,

Please note just because you may never use us does not mean that we will not help, if you have an issue following any of our help or advice (these are meant as guides only and may not be relevant to your particular complaint)just email phone or pm, our advice is free, I can honestly say 75% of the phone calls on advice is from other garages (worldwide) and owners who will not spend a single penny with us, why do we bother, those who know me understand my passion those who don't know me after speaking to me it will become very clear,


x15jq

Original Poster:

32 posts

125 months

Tuesday 29th September 2009
quotequote all
Rick, thank you very much for your response. It helped to explain things quite well. It is nice to see you have a passion for these cars!

On a good note no more check engine light, but the car still seems to have a lurching misfiring feeling to it at low rpm. Every few seconds at idle it has a shake and in top gear at around 40-50 mph it lugs if you try to accelerate, almost as if it is surging.

I think since I am in the US the next step will be a dealer, since I don't have the diagnostic computer AMDS.


rick-derby-

1,105 posts

137 months

Tuesday 29th September 2009
quotequote all
okay lets start with the basics, how experienced are you with motor vehicles, no disrespect intended, as we are dealing with the engine system generic obd equipment may help, simple checks can be easily made, when standing at the rear with the engine running, is the output from both exhaust equal, or does one appear smooth whilst the other is popping, looking at the colour of the inside of the tail pipes is one more black than the other, does the brake pedal seem harder than what is was before, has fuel consumption changed, is the fault more evident when cold or hot, has the issue just appeared or seems to be a deterioration, all can help with diagnosis, as amds is a tool to point you in the right direction so are all the other signs,

When you have faults make a note of as many factors as possible engine hot cold, wet or dry day can all be contributing factors, write them down and if you can not repair yourself pass it on it can save hours of testing plus save you labour costs, The reason i say write it down is because this can be passed on to the tech looking at the problem, human nature is what we hear, as to what we pass to someone else bears our interpretation rather than the facts, this leads to misinterpretation and faults not being rectified, and your ultimate dissatisfaction, imo the bigger the dealer the bigger the problem, more people more information by mouth passes through the more diluted the outcome, if you can talk directly to the person who is repairing the car the better chance of a first time repair,

x15jq

Original Poster:

32 posts

125 months

Wednesday 30th September 2009
quotequote all
Hi, and thank you again for the reply Rick! I am experienced with motor vehicles and perform all the maintinence to the other vehicles I have had, mostly BMW and Mercedes. I have used the generic obd2 equipment, all the 02 sensor voltages looked normal.

I could not get a read out on any mis fire codes however, yet the problem persists. It only happens hot, after the car has been run for at least 20 minutes. The exhaust feels smooth on both sides, however I noticed that the left bank of the engine has alot more oil in the intake tract (I noticed it was very wet while cleaning the throttle bodies). The brake pedal seems the same so I feel there is no vaccum leak at this time. The idle does not seem to hunt or race, it just occasionally shakes. The main issue is the surging while giving it throttle at low rpms, anything above 3000 rpm and it runs without issue.


The fuel consumption has gone up slightly since this has been happening but this could be from me driving with more gas in attempts to getting the engine to rev quicker.


Knights of Aston

311 posts

128 months

Wednesday 30th September 2009
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The car needs needs to know its misfire correction factors too. It needs them to ensure the engine runs right. Without them it can't tell if its having misfires or not. It loses these when the battery is disconnected. You'll have to carry out a coast down procedure which is not the easiest thing in the world unless you have a private road!

x15jq

Original Poster:

32 posts

125 months

Thursday 1st October 2009
quotequote all
Update:

The car still has no check engine light. The right side exhaust has a popping feel to it every 5-6 seconds. There seems to be a heavy amount of oil in the right side pcv lines which run through the throttle body as well.

I am wondering if this excessive oil in the intake tract caused the plugs to prematurely fail. The vibration is not very noticeable at idle, at this point I have been advised by the dealer to replace all plugs, coils and pcv valves which make sense.

GT119

902 posts

122 months

Wednesday 30th December 2009
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Earlier in the year my DB9 started doing the exact same thing so I called up Rick at DMS.
He sent me a diagnostics module which I plugged in for a week (car is used everyday).
Rick's diagnosis from the stored data was a poor (noisy) signal from both air mass flow meters, suggesting, in his view, an electrical issue such as a bad earth.
The problem is not as noticeable in the cold weather, so haven't dealt with it yet, but it does reappear once the engine has warmed. I'd be interested to know if you've fixed the problem yet on your car?


GaryU

34 posts

125 months

Thursday 31st December 2009
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I had a problem with my V12 DB7 Zagato. I diagnosed the problem with the Mass AIr flow reading by comparing the readings
from the two engine banks. The DB7 V12 has two separate EMU so with the correct ODBII software you can compare the two banks.
I assume the DB9 is the same. Having two banks makes fault diagnosis much easier.

On the DB7 the actual problem was rubber flashing on the new air filter causing turbulence airflow past the MAss ait flow senor.
It had been to the dealer twice. Very simple but who expects a faulty air filter.

BMS INC

3 posts

92 months

Friday 29th June 2012
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At 13,000 miles 2006 DB9, new coils, new plugs, new coolant expansion tank, cleaned the throttle bodies and now the car runs as new. No more missing

BingoBob

1,096 posts

97 months

Saturday 30th June 2012
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Is this the same car you are talking about? Did you change user name?

SLacKer

2,589 posts

157 months

Saturday 30th June 2012
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Knights of Aston said:
The car needs needs to know its misfire correction factors too. It needs them to ensure the engine runs right. Without them it can't tell if its having misfires or not. It loses these when the battery is disconnected. You'll have to carry out a coast down procedure which is not the easiest thing in the world unless you have a private road!
Anyone ever done this? Is it high rpm then let the car coast down to low rpm?

Might be a bit pricey as private roads are not cheap to buy smile

michael gould

5,690 posts

191 months

Saturday 30th June 2012
quotequote all
BMS INC said:
At 13,000 miles 2006 DB9, new coils, new plugs, new coolant expansion tank, cleaned the throttle bodies and now the car runs as new. No more missing
Is this the first DB9 on this forum that needed new coils ........I would be interested if anybody else has had coil issues with their DB9............it's well documented that it's a problem on the DB7V

3200gt

2,727 posts

174 months

Sunday 1st July 2012
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I did on mine, and I know of several others that have also.
The reason the throttle bodies need cleaning so often is that the positive crank ventilation valve on the near side always fails. Its a poor design. The valve allows oil vapour from the crankcase to outlet just in front of the nearside throttle body.
Its a 50p part but it is a bh to get at, so Aston don't bother to repair it. Its easier to clean the oil residue from the throttle body and air intake pipe every so often.
Anyone who races an DB9 disconnects the PCV outlet pipes and re-routes them into a condensation collection tank. Obviously, you also need to block off the (now open) connection points on the throttle body and air intake pipe.

code 1797 = CAN TCM/ECM Position Circuit Malfunction. Maybe caused when the electrical connecter to the throttle body was disconnected / reconnected.