Update: misfiring T5 - new DTCs

"Tim.." wrote in news:

Thanks for getting back to me, Tim.

Plugs were fitted by a Volvo dealer mechanic about 15k/2 years ago. They're single electrode with a pointy live electrode (platinum?), original Volvo plugs. Been fine during previous 15 months. Gap is 0.7mm. There is no sign of erosion, but they are jet black with soot. It *has* done quite a lot of cold start/short run cycles lately. Also, if you remember, the ECU previously flagged a code P0171, indicating *lean* running (that was before the split hose was replaced), yet the long term fuel trim keeps winding back to around -20% despite an ECU reset. So there are 3 factors that seem to contradict one another.

Dizzy cap contacts had some carbon buildup and slight pitting, so I'll replace it. I've cleaned the contacts for now but it hasn't made any difference.

BTW I noticed a bit of oil in the middle 3 plug wells. ISTR there is a known issue with this involving the breather?

Yes. I think it is also affecting performance as sometimes when I accelerate I don't feel like I'm getting any boost - it normally spins the wheels in 2nd gear every time (in 3rd on a wet road) but I'm sometimes having to wait until nearly 4000rpm before I feel any serious power. There's no sensation of a misfire when this happens. This is also sporadic - I more often get full performance.

The fact that it passed the MOT with near perfect emissions shows how hit and miss the fault is.

Nearly £10 a can at maplins but worth a go. Damn site cheaper than a scope and it does seem that it may be something that fails under hot conditions. I'll try that on the sensors and the ignition amp aswell.

Despite my vocation, I do not posess a quality DVM, only a cheapy one. I have always been able to get access to a Fluke. Unfortunately, I am between jobs ATM, having resigned from one in favour of another, which I start in the new year (hence the desperation to sort out my transport), so I can't get my hands on the appropriate gear.

AFAICS, the rev counter mimics exactly what the engine is doing, so I think the crank sensor is probably OK. The cam sensor could be a different matter though. For a crude diagnosis method, the best I can come up with is to hook up a low wattage 12v bulb to the coil LT side and observe the switching rate, if it is indeed slow enough for me to distinguish by eye.

And much less likely that I'll get it sorted myself >:-( At this stage, it looks like I'll be borrowing my father in law's car on Tuesday and dropping mine of with the local expert. His reputation is excellent, but I doubt that his fees are similar ;-)

BTW, did you see my comment re the intercooler? Is that little blow hole on the underside normal?

Cheers,

Stu

Clean / replace them, and then see.

Whats mpg like? If it is running rich, it should be drinking fuel?

I can't quite get my head around this! ECU is fuelling lean, yet plugs are black? Might be worth checking fuel pressure incase the reg is up the spout??

Leads and cap/rotor arm are of immense quality on this application (take note Mr Ford) and are usually still fine at 100k unless they've been damaged / chaffed or soaked in oil.

No- not normally.

- dismiss this for now- its probably a symptom, not a cause. Unless you have Silicone tyres, I suspect your car is running abit more boost than standard, as a stock T5 will usually only chirp in 2nd in the dry. Anyhow...

It wont be. Use a DVM of some sort with an RPM function. You can also use it on the CPS which has a square wave output, one pulse per cam-shaft revolution. (one pulse per two crank revolutions)

Possibly so, but I reckon he will be stumped if nothing shows up on the live data, but I would imagine it will. I would be interested to hear what he finds though...

The blow hole is meant to be there- its an oil drain and may well drip the odd small amount. Unless you have a reverse feed kit installed, leave it open.

The only other thing I can think of is a possible back feed of HT to the ECU from the coil which is causing it to shut down momentarily, though usually you get a jittery rev counter.

There was an TSB pertailing to earlier 850's with the twin ECU setup where the King lead was very close to the MAF cable by the air filter lid due to neither being clipped. Although the MAF cable is shielded with a braid (which should be earthed at one end-ecu- you should check with a meter) the king lead could still induce enough voltage in it to upset the ECU. You should check that your MAF wire is routed as far away from the king lead as possible, and that it is properly clipped to the air cleaner lid.

"Tim.." wrote in news:N-ednZslauCLRg snipped-for-privacy@bt.com:

The contact points where the spark fires are spotless - it's just the rest of the plug that's black. The actual plug condition is as new, but I'll replace them if you really think it is/could be necessary?

Lately, it's been a short run scenario, punctuated by £15/20 a time fuel stops, so I haven't had the oppurtunity to take an mpg reading. Besides if I fill the tank to the brim, I get a sharp pain in my wallet ;-). This will alter next week, when I start doing a regular commute of 15 miles each way (just enough to warm her up) and I'll start filling the tank and taking readings. But yes, the little orange needle does sag rather too fast for my liking.

I've been thinking about a fuel delivery problem, but I don't have a pressure gauge, let alone one with a schrader valve coupling. Nor am I sure where I'd get one and if it's worth me buying one, bearing in mind it's not guaranteed to help me diagnose my problem.

Well, as I say, the cap is serviceable but not perfect. Glad to hear about the quality, despite the make of HT leads used. Whoever said that French electrics were crap? ;-)

The most oil was in No4 plug well. Just checked the Volvo forums - the connection for the air pump used on non-turbos is between 3&4. Oil can escape here if the plug is missing or sealing badly. I'll check.

Shouldn't be, unless the wastegate rod has been shortened. I played with a boost guage a while ago and found I was getting 1.0bar = 15psi. Standard boost. Road must've been slippery that day :-)

Ahh..I thought a scope would be required to monitor the CAS. I think I'll investigate the cost of a half-decent automotive DVM. It might just be worth the investment.

I promise you I'll let you know what the outcome is when it's all sorted. The least I can do after all the help you've given me :-)

Yup - there's a nice little pool of oily crap accumulated in the undertray beneath the hole. Thanks - I can replace the undertray now that I know it's OK.

Well, the rev counter jitters, but in tune with the engine IYSWIM.

Another helpful tip. The king lead does indeed come very close to the MAF cable, although the MAF still displays a steady 4g/s of air at idle without variation. Even so, I'll try to separate them as best I can and check for induced voltage in the MAF cable shield.

Stu

Unless you're giving it hard use then a cheap a-D on the computer can do most of what you want to do with a scope. Picoscope make nice ones for way less than my flukes cost.

"Duncan Wood" wrote in news: snipped-for-privacy@lucy.domainnotset.invalid:

I see that they do a 2 channel automotive scope for £400. Whilst I'd love to own one, I can't afford or justify that sort of expense when I don't diagnose engine management faults on a regular basis.

The automotive meter from maplin for £26 is more up my street, and a can of freezer spray. If I don't get anywhere with those, at least I can still take the car to someone who *can* diagnose it for me and after that I'd still hope to have spent less than £400!

That's meant as a polite criticism, not a flame, BTW :-)

Stu

Fair point, but you don't need the automotive kit, any cheap A-D will do.

Diagnosis is now complete. The local Volvo specialist is working today, so I went down to see him. He used a Volvo specific code reader to pull

- EFI-414 Boost pressure control. Faulty Signal

Glad to know you finally found the cause.

And note how it wasn't the boost sensor that was faulty. This is a classic example of why fault codes should be taken with a pinch of salt. The engine knows that it needs x amount of air per revolution at 1bar (2500cc in this case), so it expects to see an amount of airflow from the MAF sensor, that is proportional to the boost pressure (or MAP) sensor. So if one reading goes out of limits, then the ECU knows something has gone wrong, but it doesn't know what. So it goes into a reduced output mode that is least likely to result in engine damage (if it had a faulty boost sensor that didn't show true pressure and it stopped looking at the airflow, it could lead to an overboost situation, so instead it's programmed to look at the sensor that's going to produce the safest running conditions for the engine, and will log a fault accordingly)

I'm sure some suitable refreshments or beer tokens wouldn't go a miss ;-)

That's the benefit of having good datalogging facilities. On a live data plot, that would stick out like a sore thumb.

Pretty much the problem in a nutshell.

Could also try GSF, and EuroCarParts. They do a lot of vairous sensors, but probably best to get it from the Volvo specialist since since he did find the problem for you for no charge.

That's the reason why good equipment costs a lot of money, and why it's only any use if used by someone who knows what they're doing.

No problem. We enjoy the occasional challenge. It's makes a change from the usual problems around here.

E.g. Pinking Micra's.....

Tim..

I've not been much help, but I've actually been following this thread with much interest. Sorta sad to see it's came to an end, though! Glad you've got (or are getting) the damn thing sorted, finally!

"moray" wrote in news:en0gsh$7ij$1$ snipped-for-privacy@news.demon.co.uk:

Yup. It was the VADIS software that linked the DTC to the probable cause. Ironically, I (allegedly) have a copy of VADIS on my home PC, I just don't have a Volvo specific FCR.

Deffo. Always pays to keep good people onside.

I can set up a data plot on the laptop, but the battery is shagged these days and I only get a few minutes use from it. Just enough to clear codes and check sensor readings. Not enough to sit around and wait for the fault to appear. Last year I used this facility to diagnose an over- active secondary O2 sensor on the wife's Yaris. It indicated a bad cat and flagged a fault code saying the same, but the car flew through the emissions test. Hence I circumvented the sensor using a pair of carefully selected resistors. The MIL hasn't been on since.

The problem I find using OBD is that due to the limitations of the RS232 interface, the sampling rate gets very poor if you try to monitor several sensors at once.

ECP do the original BOSCH one for £223 or a cheapy one for £117. His price is about half of Volvo's so about £150. I'll go with him for loyalty and convenience (nearest ECP is about 15 miles).

Stu

"Sandy Nuts" wrote in news:15Qkh.22222$ snipped-for-privacy@text.news.blueyonder.co.uk:

Hehe....thanks. I usually lurk in the background, but when I raise a new thread, it often turns into an epic :-)

Stu

I thought it was a pinking punto, or cinquo or some such fiat junk? Thankfully we've not heard from pinking peter recently ;-o

"Moray Cuthill" wrote in news:4594624f$0$15440$ snipped-for-privacy@free.teranews.com:

Hehe.....yes, I remember him. Was it the 1.1 FIRE model he had? SWMBO had the same engine in her Sei. Every one I've come across sounds tinkly. Doesn't stop them from delivering decent performance & economy, though.

Stu