Vehicle details: Vauxhall Signum
Year: 2003
Symptom: Engine misfire,
Author: Dave Hill |

Vauxhall Signum | Misfire

A 2003 Vauxhall Signum (same as a Vectra C) arrived at the workshop with a slight misfire and a more general flatness under acceleration. A scan provided the code P0301 (Cylinder 1 Misfire Detected) and a quick inspection confirmed that the insulation had failed on the cylinder 1 coil area.

A new coil pack and set of plugs cured the single cylinder misfire, but still there was a general flatness in performance on the road. When I rescanned it, there was a new code P1191 Unknown DTC.

This is a new system to me and some head-scratching began. This is a direct injection setup where a pump in the tank supplies a high-pressure pump driven by the inlet camshaft. The low-pressure pump delivers approximately 4 bar (64 psi in my case) and the high-pressure pump boosts this pressure to a maximum 120 bar (1740.5 psi).

The fuel rail resembles a common rail diesel setup, with a pressure sensor (3-wire) and a pressure regulator (2-wire). I set about taking a capture of both these components in an effort to understand what was wrong.

Here you can see the duty cycle increase as I floor the throttle but the pressure sensor output doesn’t rise as I expected.

Unfortunately I don’t have any kit that will physically test the pressure in the rail but I needed to prove if the sensor was capable of reacting to a pressure increase, so I used the workshop airline pressure to test it and sure enough I got a reaction, however small.

The ironic thing is that I had had three of these vehicles in recently with various faults and I have missed the opportunity to take captures of various systems to gain the knowledge needed.

A few days later…

A new pump arrived after getting lost in a trolley at Luton for two days! Anyway, it sorted the problem as expected.

Here is the same capture as before, but now the pressure sensor reacts to throttle demand.

I did manage to strip the high-pressure pump (once it was condemned) and the failure was due to a small perforation in one of the three rubber pumping diaphragms.


10 comments | Add comment

March 29 2015

would that have showed up scoping oxygen sensor and seeing it stay low during hard acceleration too?

Dominique van Wyk
August 05 2012

Hi, i have this p1191 error on my car as well except that i have a Alfa Romeo 147 JTDM, my experience while driving the car has been increased smoke, incread fuel consumption and also flatness and slowish response on wide open throttle, after driving a while and one wide open throttle session or so on a warm day the problem will kick in and engage limp mode. what i have noted is that in cold weather the fault does not come up but the rest of the symptoms remain, could my HP pump also be faulty maybe? sorry i know its a diesel so a bit off your story here but you seem like someone who really knows his stuff and im struggling to find anyone knowledgeable on these sort of things in South Africa

Dominique van Wyk.

Morten Sinding
March 04 2010

I have a customers car with 3 faults:
P1191 and after a test drive I got this:
Fuel rail pressure at idle was 4990 KPa I will be back later Yours MS

February 17 2010

First Class Hinweis leicht zu verstehen und nachzuvollziehen super

Paul Whatmough
November 09 2008

First class repair Dave. Very informative and as usual well presented and easy to understand. Thanks for taking the time to put this together keep up the good work.

Fernando Ramos Vergel
October 29 2008

The problems with GDI are common in Peru.
Your waveforms will help me when these cars flatnes in a wide open throttle.

solomon khan
October 29 2008

As with any new [cutting edge] designs,there will always be frontiers to cross. Thanks for sharing.

Mike Gove
October 29 2008

Very nice job.

Devon Sampson
October 22 2008

Great information, this engine must be similer to 3.5 direct injection Isuzu engine in the USA.

Stuart Duff
October 21 2008

Very informative and usefull too. Many Thanks

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Case study: Misfire