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Perplexing Misfire. Only when started warm

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cfoss
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Perplexing Misfire. Only when started warm

Post by cfoss » Mon Sep 23, 2019 4:00 pm

Hi all. I have a 2000 V70XC with the 2.4T.

It is my first Volvo but I am an active mechanic--I take care of all my vehicles and have modified/turbo'd vehicles etc...

BUT, this one has me scratching my head a bit.

When cold, it starts and runs great. Smooth-no issues. It will continue to run this way for the length of time it is run.

If it shut down for a period of time, say 30 minutes, then when started again it runs rough--definite misfire. Sometimes it recovers and smoothes out, sometimes not.

But it will always run well again if left to cool. At first I was thinking leaking injector, and/or heat soak causing vapour lock in the fuel system. It could still be that, but I think it's unlikely.

Do these cars have issues with stuck EGR valves? Seems like that's a possible culprit? I have codes for misfires on the ignition, and also 'open circuit' codes for the injectors, but my experience has been they either work or they don't (Especially the injectors). Is this true for Volvos?


Thanks,

Chay Foss



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Re: Perplexing Misfire. Only when started warm

Post by abscate » Mon Sep 23, 2019 8:18 pm

Your 2000 won’t have EGR, Volvo engineered that out years before.


These problems do suck to troubleshoot, so you have to try to sort out by monitoring parameters with either a good scan gauge or VIDa, Volvo software.


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Re: Perplexing Misfire. Only when started warm

Post by RickHaleParker » Tue Sep 24, 2019 5:14 am

cfoss wrote:
Mon Sep 23, 2019 4:00 pm
I have codes for misfires on the ignition, and also 'open circuit' codes for the injectors.
Metal contracts when cold, expands as temperatures rise. Check the condition of the connectors. Are they clean and tight?
You might want to measure the resistance of the injector both cold and hot.


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Platform: X40 (Nedcar) 2003 S40, B4204T3, AW55-50/51SN, Siemens EMS 2000. Plant: Born Netherlands.

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Re: Perplexing Misfire. Only when started warm

Post by oragex » Tue Sep 24, 2019 7:31 am

How is the fuel pressure at the rail at the moment of hot restart ? I'm thinking about the fuel pump on this one - of course, just an idea. Injectors are pretty solid on these cars. Another area, maybe a coolant temp sensor ? Does the needle climbs steady when warming up ? The wires near the connector can also crack



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Re: Perplexing Misfire. Only when started warm

Post by mrbrian200 » Tue Sep 24, 2019 8:58 am

Something's sensitive to heat soak. Once you've checked the initial 'basics': fuel pressure and/or intake air leaks, assuming there are no problems there, this will be very difficult to trace without a good diagnostic tool. To start you need to look at misfire codes/counts to at least figure out whether it's one cylinder doing it (and which) or whether miss is randomly spread across all cylinders.



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Re: Perplexing Misfire. Only when started warm

Post by cfoss » Fri Sep 27, 2019 9:27 am

Thanks for the ideas guys. Yeah it's some type of heat soak for sure. I'll check the CTS but there is no indication form the guage of any issues. Do they use the same sensor for the ECM and the guage? I've seen it both ways.

I have checked both the injector connectors and the ignition coil connectors-they were fine. Better than expected actually. I should have checked the resistance values but I had to reassemble to use it....I'll check there next.

I have to get it misfiring then start checking what cylinder(s) are misfiring by pulling coils etc. Can you just disconnect the coil low voltage leads or will this harm the electronics? I guess I could just pull the coil screws then remove them one at a time.

If the misfire is random then it pretty much has to be fuel related. Whether it's low pressure, high pressure (excessive rich), air in the lines or some type of sensor failure.

It always screws up at an inopportune time---like I'm in a hurry or whatever. Then it will run great when I have a chance to troubleshoot. Frustrating!

Oh well, keeps me out of trouble ;)




Chay



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Re: Perplexing Misfire. Only when started warm

Post by cfoss » Mon Sep 30, 2019 8:28 am

I removed the cover plates for the coils and the injectors. It hasn’t run rough but it failed to start for about two tries then fired right up and ran great

I feel this must be a fuel issue. Didn’t have the correct adapter for the Schroeder valve to check the fuel pressure but I think I’m probably looking at a small leak some where or a pump

Hard to find though! There is no fluid dropping anywhere



Chay



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Re: Perplexing Misfire. Only when started warm

Post by mrbrian200 » Mon Sep 30, 2019 9:43 am

Considering your last post (no start first two tries, then started right up). I'm assuming the hood/bonnet was open. Check the crank and cam position sensors. They're hall effect sensors with an internal magnets. Those man made internal magnets lose magnetic flux as they age. The hotter they get, the magnet gets weaker but will recover somewhat as they cool. If it's teetering on the edge the heat soak condition/hot restart will often be the scenario where you'll start seeing trouble. On a cold engine, or whilst driving due to airflow through the bay, the sensors produce a strong enough signal for the ECM to read accurately.

This is just one possible theory based on your description. Don't consider it a 'firm diagnosis'.

I still advise you get hold of a decent scan tool to look at misfire codes/counts. If there is a high misfire count contained to one specific cylinder I'd look at the injector and it's harness connector first, followed by the ignition coil and it's electrical connections. The ground wires for the coils can become contaminated by engine oil leaking from the filler cap and cause trouble there too.

For these 'funky/difficult to nail down the cause' issues I'm big on pulling spare sensors/injectors etc from salvage vehicles to test/try. Otherwise throwing new parts at it gets needlessly/pointlessly expensive fast. Once you find the cause you can order the one offending part as new if you're not comfortable leaving a used part on it.



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Re: Perplexing Misfire. Only when started warm

Post by cfoss » Thu Oct 17, 2019 12:20 pm

I pulled the engine covers, in order to troubleshoot the misfire when it was happening-I have not had it happen since. It had been two weeks, so I thought maybe the cover was holding heat and the coils are the issue. That symptom doesn't quite match, given that when it doesn't start I get no cylinders firing, and I would assume that not all the coils could go intermittently bad at the same time, but no news was good news.

But just recently my wife said it was running 'funny' again. I guess it was telling a joke of some kind? I hate these type of descriptions lol.

Anyway, looks like the joke is on me...we still have an issue. Thanks for the info about the cam/crank sensors. We have no Volvo wreckers near us so that solution is out, but I will have to try throwing parts at it a bit I guess. It's so freaking intermittent it sucks to troubleshoot.

Hopefully something will just finally die and I can find/fix it.


Chay



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Re: Perplexing Misfire. Only when started warm

Post by RickHaleParker » Thu Oct 17, 2019 2:59 pm

Vida-DiCE to look for inactive DTCs might be informative. Inactive DTCs can tell what has happen but is not currently happening.


Platform: P80 1998 C70, B5234T3, AW50-42, Bosch Motronic 4.4, Special Edition package, Plant: Uddevalla Sweden.

Platform: X40 (Nedcar) 2003 S40, B4204T3, AW55-50/51SN, Siemens EMS 2000. Plant: Born Netherlands.

Platform P2 2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0, Plant Torslanda Sweden.
----------------------------------------------------------------
1997 S90, B6304S, AW30-42, Bosch Motronic 4.4 - Sold

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