Sick 172 :( - Bad misfire problem

[Daveca4]

Hi Guys,

First, I'm new here so want to say hi

I have a sick 172 PH2 that I'm having trouble getting well. The problem I'm having is a really bad missfire and very jerky/shaking rough idle. The car also likes to kangaroo when in any gear - for example 4th gear at 30mph where you would expect to just drive normally it will jump all over the place.

I borrowed a fiends clip for a day but unfortunately there were no codes stored.

Replaced so far:

Coil pack
HT Leads (Euro car parts)
Spark plugs - NGK
Map sensor
TDC Sensor
Throttle Body
Pre cat Lambda
Cylinder 3 Injector

The only time i did get anything code wise was a cylinder 3 misfire which prompted me to replace the coil, leads, sparks which didn't make a difference then eventually the injector... but again no real difference in how the car runs but the code has never been back since.

I still need to do a compression test but I'm scared to do so in case this means big bills I'll try it this weekend hopefully

I have noticed something strange between 1000 and 2000 rpm which just happens to be when the car is at its worst - which I've uploaded to YouTube https://www.youtube.com/watch?v=FYCVDKvAGak&feature=youtu.be The pedal is still at this point - the needle is jumping around by itself. This is also the point in the rev range where the kangaroo thing i mentioned is at its worst no matter what gear you're in.

Also, here is a video of the idle https://www.youtube.com/watch?v=Z6KrguRtDns&feature=youtu.be

And, here is a video of the engine shaking around https://www.youtube.com/watch?v=-_GuXcWr6LA&feature=youtu.be

I've had the car lose all power when the rev range is in-between 1000 & 2000 rpm where the accelerator pedal does nothing.. this last for a few seconds and then car splutters back to life. The car is pretty smooth above 3000rpm

I'm not getting any noticeable loss of power nor is the car smoking from the exhaust.

I'm looking around Edinburgh to see if there are any decent specialists that can help me out so any recommendations are welcome. I'm hoping I've missed something obvious and you guys can point me in the right direction before i do though

Any help would be greatly appreciated!

Thanks

Dave

 

[Oscar88]

dave i'd have a look at your fuel filter it may be blocked and the fuel pressure to tick that off the list. curious to know if you can get the car past 1-2k revs? is that the maximum it'll do with this missfire? throttle positioning sensor could be another probable cause dave

 

[Daveca4]

Thanks, i haven't checked the fuel filter - how easy is it?

It gets past 1-2k revs without issue - i can drive it fine on a motorway at 70 and you wouldn't think there was a problem. it's just rough as hell around town and judders all over the place

 

[jase.ph1]

Did you use new parts or second hand ?

 

[George182]

dave i'd have a look at your fuel filter it may be blocked and the fuel pressure to tick that off the list. curious to know if you can get the car past 1-2k revs? is that the maximum it'll do with this missfire? throttle positioning sensor could be another probable cause dave

Fuel filter is inside the fuel pump on these isn't it?

 

[Oscar88]

Fuel filter is inside the fuel pump on these isn't it?

on a 182 it's apart of the fuel pump, on 172 phase 1's from memory (its been a while!) they aren't in the fuel pump pump, they are in the usual fuel filter location after the fuel pump and phase two's are in the same location as 182's i believe. the 182 fuel filter is the trickier one to change

 

[Big P Dog]

I reckon if it was a dodgy fuel filter the problem would occur throughout the rev range. I imagine it's a problem with the ignition system. I had a similar problem and it was an injector. When you took the plugs out, were they all the same colour? Nice light brown? You can check the injectors by putting an ammeter across the two tabs inside the connector and reading for between 12 and 16 ohms resistance. You should get a constant reading after a second or so and they should all be vaguely similar.

Another similar issue I had was wires melted between the MAP sensor and ECU but this caused the car to cut out. If taking it to a specialist, I recommend Rentec at Leith. They did a great job on my car and were very reasonable too.

 

[Daveca4]

Hi Guys,

thanks for the recommendation. I'll take it to Rentec guys and see what they say. I checked the plugs today and 3 of the 4 we're dry carbon fouled so it's running way too rich.

I couldn't do the compression test today since the tester i have is 14m hopefully the rentec guys can help me out

thanks

Dave

 

[Ryanph1rs]

Tried a temp switch ? As that controls fueling when it's cold aswell to act as a choke" if you will ..... Sounds small to cause such a bit problem but it's usally the little things that do this

 

[Daveca4]

I have a temp switch to swap out but haven't got round to it. The temp gets up to running temp ok and stays there so I wasn't sure it would make a difference but will give it a go. At this rate I'm going to end up replacing all the sensors

thanks

dave

 

[D4w5on]

have u got this issue sorted because mine does the same