Miss­ing a beat

Car Mechanics (UK) - - Diagnostics Doctor -

I have a 2004 Vaux­hall Signum 2.2 di­rect petrol auto with the Z22YH en­gine and 99,000 miles. Re­cently, it has felt as if the en­gine was oc­ca­sion­ally miss­ing a beat and the idle was a lit­tle lumpier than usual. Then the ‘span­ner in a car’ sym­bol il­lu­mi­nated on the dash and, shortly af­ter­wards, the en­gine lamp il­lu­mi­nated. The run­ning be­came very poor, un­til the car would only jud­der along at 5mph. Turn­ing the en­gine off and on re­stored nor­mal oper­a­tion, but the en­gine lamp re­mains on.

My £15 scan­ner showed no er­ror codes, so I bought a Foxwell NT414, which has high­lighted ‘P1191-52 – Fuel pres­sure sys­tem mal­func­tion’ and ‘U2103-70 – Can-bus mode no com­mu­ni­ca­tion’. This would seem to in­di­cate a faulty fuel pres­sure sen­sor (is this the MAP sen­sor?), fuel reg­u­la­tor or high-pres­sure fuel pump.

It rec­om­mends check­ing the fuel pres­sure us­ing Tech 2, but is this some­thing I can check with my NT414? Also, should I re­place the sen­sor first and see if that helps or do I need to get the fuel pres­sure checked? In­ci­den­tally, the fuel fil­ter was re­placed about six months ago. Af­ter clear­ing the codes, it took four at­tempts to start the car and then it ran quite roughly. In traf­fic, it would hardly pull at all, but putting it in neu­tral and revving the en­gine seemed to re­store nor­mal ser­vice. The ‘span­ner’ sym­bol dis­ap­peared and just the en­gine light came on. When I got home, I checked the codes again and a third has ap­peared: ‘P0302-01 – Cylin­der 2 misfire de­tected’. Rob Veltze The MAP sen­sor is a dif­fer­ent com­po­nent to the fuel pres­sure reg­u­la­tor. The MAP sen­sor de­tects man­i­fold air pres­sure, while the fuel pres­sure sen­sor mea­sures the fuel pres­sure in the fuel rail. The code ‘U2103-70 – Can-bus mode no com­mu­ni­ca­tion’ may be an un­re­lated prob­lem. It usu­ally in­di­cates a fault with the col­umn in­te­grated mod­ule (CIM) – this is a com­mu­ni­ca­tion hub for the ECU and sys­tems.

Given the fuel pres­sure codes and the misfire, there are three likely causes of the prob­lem. The first is that the in­jec­tor for num­ber two cylin­der is faulty. The sec­ond is that the fuel pump has failed. The third is that the pres­sure re­lief valve at the end of the fuel rail is stuck or bro­ken, al­low­ing loss of pres­sure.

Pro­vided the sen­sor is work­ing cor­rectly, your NT414 should be able to read the fuel pres­sure from the live data. The fuel pres­sure should run at be­tween 4.0-4.4 Bar, and if you are get­ting suf­fi­cient pres­sure and have elim­i­nated the above pos­si­bil­i­ties, I would check the in­let sys­tem for any air leaks. If you are in doubt about the ac­cu­racy of the fuel pres­sure read­ing, it may be worth get­ting the pres­sure checked us­ing a gauge.

An­other pos­si­bil­ity is that the EGR valve is faulty, but if this were the case I would ex­pect to see a mul­ti­ple misfire as op­posed to the sin­gle-cylin­der misfire that has been de­tected. UP­DATE I re­ceived an email from Rob Veltze say­ing that, af­ter hav­ing the fuel pump over­hauled, the prob­lems were rec­ti­fied.

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