Can serpentine belt slip cause misfire?

[hedges88]

I have had one small issue with my otherwise lovely 2003 Mitsubishi Galant Estate 2.4GDI. When I bought it there was a slight misfire on cyl 3 and according to the service log the issue had been rectified before though sadly not what was done. I changed the individual coil plug to another cylinder, problem stayed with number 3. So my thinking after checking the spark plug was okay etc that next I'd need the injector inspected, seemed like a logical next step. Knowing nothing about GDI engines unfortunately that meant taking it to a Mitsubishi service centre.

I noticed very very oddly that the issue was virtually eliminated in wet weather, the wetter the better. EML would even go off. This is polar opposite to every problem I have researched. I've noticed a bad and rapidly worsening squealing of the serpentine/aux drive belt. It just seemed like an embarrassment that a bit of WD40 belt restorer would quiten. Today the belt started squealing really bad as I accelerated suddenly. I got sudden and bad misfire, probably on more than just one cylinder to be honest it was rough. Now I didn't notice the battery/alternator light come on but is it possible that when the belt is slipping the coils are somehow not getting enough electricity and therefore the misfire is happening because of the electrical problem, either lack of electricity or sudden varying amounts of alternator load/voltage output.

This is a pretty simple beast pre-canbus. It has an ECU yes but it also has an ignition control module which is separate to the ECU. Is it possible I have accidentally diagnosed my own problem, would wet weather make a serpentine belt more or less likely to slip?

If anyone knows I would be most grateful

[Polly Grigora]

yes, the voltage will be low when the belt is slipping, how low is an unknown

[LarJammer]

Could be similar to a phenomenon that affects Porsche dfi engines (09 to 2013). If the wrong length belt is used, it causes a resonance / vibration that the ECU pick up as a misfire.

[trashbat]

I would think it's more likely that your original theory of blocked injectors and overall GDI carbon buildup is to blame.

[hedges88]

trashbat said:

I would think it's more likely that your original theory of blocked injectors and overall GDI carbon buildup is to blame.

It most certainly could be the failing serpentine belt or tensioners and an injector problem as well, both issues together. Just seems strange to me that it seems to go away in the rain or at least improve a lot. The wiring that goes to the coils is pretty old and wrapped up in insulating tape I've not really wanted to get that far into it and make it worse but I guess I might have to cut the insulating tape open and see what's going on and do my best to do a good job of neatening them up maybe heat shrink wrap them to see if things improve or worsen. I'm not happy to continue driving anymore I have fears about unburned fuel reaching the catalyst. The misfire is most prominent when it starts up just a light little shake at idle here and there doesn't occur in the upper rev ranges much and on a wet day once the engine has been on for a while the problem seems to get worse possibly due to heat. I think I might get a bottle of water with a mister and have a little spray under the bonnet in darkness and see what illuminates if anything. I took the plug out and cleaned it, soaked in WD-40 all night and used a metal wire brush to clean it all off and it looks much better now but I will post some pictures of what it was like. Maybe it's condition will point to a fuel problem or not? I know some people are good at "reading" spark plugs to determine what's going on in that cylinder based on the colour and the way the yellow stuff for the black stuff builds up and where I don't really know a lot about them...

[trashbat]

I say that to you because I had an Alfa 156 JTS, one of the first DI engines, and I suspected and tried a lot of different things like wiring looms before having to accept it needed ultrasonic injector cleaning and a head-off decoke. There are photos of it somewhere and it was pretty bad. I don't know Mitsu specifics but I'd imagine yours is similar.

[stevieturbo]

trying to clean precious metal plugs with physical trauma...ie, especially a wire brush etc, will always cause more harm than good.

If the plugs are old, fit new plugs. If you've damaged the plugs by trying to "clean" them, fit new plugs.

[GreenV8S]

You mentioned WD-40 a couple of times.

WD-40 is good for stopping your tools rusting and making them smell nice.

It has no business anywhere near your plugs or drive belt.

If you take the plugs out and they don't look new or nearly new, refit new ones correctly gapped.

If your belt is slipping, replace it. Belt dressing spray or bar soap rubbed over it can improve the grip temporarily until you get round to replacing it. Oil will stop it squealing but not stop it slipping - it may also degrade the belt.

If you're able to swap the coil and plug leads between cylinders that would show whether these are contributing to the problem.

[hedges88]

trashbat said:

I say that to you because I had an Alfa 156 JTS, one of the first DI engines, and I suspected and tried a lot of different things like wiring looms before having to accept it needed ultrasonic injector cleaning and a head-off decoke. There are photos of it somewhere and it was pretty bad. I don't know Mitsu specifics but I'd imagine yours is similar.

I'm afraid not, the Italians will tell you that they invented basically everything if you let them. Now this kind of thing I am good with

The 1955 Mercedes-Benz 300SL became the first road car with direct injection. Then the 1996 Mitsubishi Galant featured a smaller version of my engine with GDI for the first time and it was the first car to have GDI. Now that I know.....

I can't even see where it injects the fuel, I see where the spark plugs go I look further back at the engine and I can see something back there but no fuel lines or anything that I can see where the bloody hell does it inject the stuff. It's got a really deep block the spark plug sort of had to be lowered in like it was spelunking into a cave so maybe it's somewhere else?

Now I'm well aware of GDI engines positives and negatives , one of the reasons I bought this car is because of its unbelievable service history and it has always had a complete engine flush, fuel system treatment etc from Mitsubishi at each and every service, always run on premium fuel and also had a catch can fitted which is essential for GDIs. Now it is basically due it's next service and needs the timing belt and the balance belt so I'm thinking I might just get the serpentine belt & power steering belt done at the same time but I don't want to drive it to the Mitsubishi maintenance department with this misfire. I do have my own boroscope that attaches to my phone it's just like a Chinese thing nothing fancy but I could take some pictures of cylinder 3 and upload them just for a test

I've got no bloody workshop manuals for this thing. The American version is useless they don't have GDI they were built in Mexico and aren't even the same car basically. If I break something it could possibly be that there are just a handful of these parts available if it's something specific to the Galant and nothing else that is. I got rid of my Volvo because I was not confident to do diesel fuel injectors, are petrol injectors any easier or more forgiving to work with?

I will order four new plugs following some advice from above, to be fair it didn't hurt it or make it worse but yes I should have been more gentle with it I think people used to use that black sandpaper?

As for ordering new plugs what a bloody nightmare. I thought that the gap was really important that it was set right and it's usually set with new plugs straight out the box. Look at all these different various gaps on just a handful of the plugs available......Do I get one that's a Poly V TIT or what

These champions come as a set of 4, they are a good brand and they are cheap so I'll order them if they work?

[hedges88]

GreenV8S said:

You mentioned WD-40 a couple of times.

WD-40 is good for stopping your tools rusting and making them smell nice.

It has no business anywhere near your plugs or drive belt.

If you take the plugs out and they don't look new or nearly new, refit new ones correctly gapped.

If your belt is slipping, replace it. Belt dressing spray or bar soap rubbed over it can improve the grip temporarily until you get round to replacing it. Oil will stop it squealing but not stop it slipping - it may also degrade the belt.

If you're able to swap the coil and plug leads between cylinders that would show whether these are contributing to the problem.

I'm not great at mechanics but I'm a little bit better than that. I was referencing WD-40 belt dressing to try and keep it from slipping so I could get it to a garage and there's nothing wrong with using that that's a product that's not oil-based I'm assuming because I know that spraying belts with oil is the last thing you want to do so that would probably be the appropriate product for the job. That said I've just finished revitalising all the door and window seals and I still have some Gummi Pflege left that might quieten it. That basically restores rubber and I believe is water-based.

I already did swap the coil the problem stayed on the cylinder so not the coil I think I mentioned it but if I didn't I apologise

[trashbat]

hedges88 said:

I'm afraid not, the Italians will tell you that they invented basically everything if you let them. Now this kind of thing I am good with

The 1955 Mercedes-Benz 300SL became the first road car with direct injection. Then the 1996 Mitsubishi Galant featured a smaller version of my engine with GDI for the first time and it was the first car to have GDI. Now that I know.....

Hence "one of the first" JTS was 2002. Mitsubishi were indeed first of the modern era and there were a small handful of other manufacturers releasing them between those points.

Photos of mine, now long gone, are at http://crap.wapoc.com/jtsrebuild/

[stevieturbo]

hedges88 said:

I will order four new plugs following some advice from above, to be fair it didn't hurt it or make it worse but yes I should have been more gentle with it I think people used to use that black sandpaper?

No, people do not. People do not try and clean precious metal plugs.


As for Champion plugs, never liked them

NGK or Denso always.

[hedges88]

Well it's all sorted. I'm driving to my friends this evening and suddenly, Bang! Alternator lights and everything else light up the dash like an Xmas tree. I'm suddenly faced with turning into a side road trying to overcome a disabled power steering system. AA says it's going to be like 2 hours and my friend was close by so I limped it to hers watching the coolant guage climbing very slowly as expected. A few minutes away from her I loose my headlights in the dark and the transmission had started acting up. I just rolled up and parked coolant nowhere near red. I waited for the AA and initially wanted it taken to a dealership for repair under my AA breakdown repair warranty but was NOT happy with the decision to tow it. According to their system Mitsubishi say it can go 19 miles up to 30MPH. It's not a regular autobox, the fact most do 30 miles and it does less is a clue to fragility in my mind. Also we did not want to leave it outside a closed dealer for security. Bonnet gets lifted the belt is still there! Turns out to be another belt running transversely Infront of the engine to do PAS, AC and something else we don't know. Good news is they are coming tomorrow morning to replace not only the belt that snapped but also to replace the Aux Drive belt in place. If less or around my excess then I'll pay for parts if over I'll just claim.

With the belt snapped it idles a hundred rpm less or so smooth as butter no misfires or jolts once stationary. I'm hoping indeed these misfires have been connected. Bolts for tensioners look a little shot but they should be able hopefully to sort it in place.