1.4DTI Wiring Causing Misfire

G

garywoods

Member
My 1.4 TDI 75 A2 has once or twice shown a 'misfire' whereby the engines seems to be running rough, poss on two cylinders and this seems to be related to damp conditions.

Upon investigation there is a round electrical connector with 4 wires which goes to the top right hand side of the cylinder head /cam cover(as you look at the front of the car) if this is 'waggled' the engine will go back to normal / reinstigate the issue. Could someone explain what this connector actually controls? senses? goes to? Has anyone come across this before.

In addition to this there is a warning light which comes on which i believe is actually the traction control light. Any ideas? what exactly this is. Im almost certain the problem lies within this connector / small area of the wiring as it can be made to go away by agitating this connector. As other than this the engine drives fine.

One further question i have is on the left hand side of the engine bay there is a unit which has some silver corrugated pipe work (looks like aircon ducting but it isnt as i havent got aircon) going into and from it. One of the pipes is clipped down to the very bottom of the car and doesnt appear to connect to anything? any ideas what this is and whether it is normal for it not to connect to anything it has a jubilee clip on the bottom. Theres no obvious place for it to connect and it is causing me no issues.

Many Thanks In Anticipation.

Gary
 
Hi Gary, welcome to the A2oc
From your description I'd guess the connector is for the electronically controlled fuel injectors. This connector links to a small wiring loom which runs inside the rocker cover and this loom has caused problems on a couple of members TDi's.

Sorry i'm not sure if the warning light activation is linked.

Assuming you have an early (2001 - 2002) car then this unit is the auxiliary coolant heater. It's diesel powered and works like a mini central heating boiler. Unless you use the Econ button it switches on automaticaly in temps below approx 5 deg for faster warm-up and improved heater performance.

Cheers Spike
 
Thanks for your reply spike much appreciated. It would certainly make sense for it to be related to the injectors as presumably this would be a prime candidate for the 'missing' if they werent firing. Would be good to hear of members experiences of this.

The male part of this connector is indeed fitted to the rocker cover and the female part is the removable section which seems to remove the problem when agitated. I guess the wires then run inside this and down to the injectors? Do you know what the three little black plugs on the front face of the engine are? (my knowledge of diesels is not great but they look like the equivalent of injector connectors on a petrol and they connect to things that are screwed into the head). Are these the glow plugs?

Gary
 
Spike,

I have the injector harness now. Which has the connector which goes to the ecu and the three little plugs to the injector.

I was wondering how much of a job this is to change? it looks relatively straight forward. But at first glance it looks like the wiring sits under the 'rocker' cover and the connector flange screws to the head.

I havent had chance to look further due to weather generally being rubbish but plan to tackle it this weekend with my dad. If rocker cover etc. has to come off i will need to sort gasket etc..

Any advice would be greatly appreciated although when i look closer it may become more obvious.

I just want to get back driving!

Regards

Gary
 
Hi Gary
I have not replaced an injector harness personally but think it should be fairly straight forward and just a case of feeding the wiring through drillings in the webs of the head casting.
In theory the (expensive) rocker cover gasket is re-useable so i'd be tempted not to replace it unless it leaks.

CheersSpike
 
Ok guys thought I would follow up with fault codes part changed etc so that it could hopefully be useful for someone else one day.

The following fault codes were logged:

18075 - Valve for Pump - Jet: Cylinder 2 (N241): Electrical Malfunction
16686 - Cylinder 2 Misfire Detected
18074 - Valve for Pump - Jet: Cylinder 1 (N240): Electrical Malfunction

which according to the ross tech wiki is as follows:

Possible Symptoms

Irregular rpm

Possible Causes

Wiring and/or connections to/from the Valve for Pump Jet
Valve for Pump Jet

Possible Solutions

Check wiring and Check / Clean all connections
Replace the cable-tree to/from all the Valves for Pump Jet
Replace Valve for Pump Jet (replace them all !)

Special Notes

For each Valve the ECU checks the Begin of Injection Period (BIP) via a voltage. That voltage is very small (less than 0.0001A). Each extra resistance in the cable is fatal. So, in case of any doubt, just replace all cables.


I changed the injector harness (35 quid + vat) which lives under the rocker cover as per suggestions from the guys on this forum. And 300 miles + later I can confirm the fault has not re-occured (it was getting regular every journey in the end). The fault being the ABS light and ASR light coming on along with the beep and exclamation mark, coupled with a nasty missfire.

The cable lives in pretty harsh conditions (heat, oil and vibration) and was looking a bit tired, bare wires showing from the crimp terminals etc. Job was pretty easy to do once you figure out how to get the air inlet out of the way!

Thanks for the input spike.

Gary
 
Hi Gary

Thats a great result. Thanks for providing an overview of the problem and the fix as this type of feedback is just what we need to improve the knowledge base of our club.

Cheers Spike
 
Interesting reading. My 2001 1.4 TDI has exactly the same problem which I was trying to diagnose today. Fault codes P1666 No1 injector and P0301 misfire.
I have noticed that once the engine has started to warm up, switch off and restart. This will clear the ABS and ASR captions and the shortly afterwards the engine runs normally.
A bit of searching on the net quoted a resistance of 0.5 ohms at the injector. Add 0.3 to 0.5 ohms when checking via the harness.
Today I put my multimeter on the pins in the plug mounted on the side of the engine. Bottom left was the earth and on checking across the other pins I got 0.8 ohms, 0.8 ohms and 0 ohms. Found the problem. Warmed the engine up, switched engine off then on, cleared the ABS/ASR, engine running normally. Re-checked the plug and now all 3 pins were reading 0.8 ohms.
Next step - is it the harness or the injector. Only removing the rocker cover and checking the resistance at the injector will tell.
Based on the information above from Gary about the harsh environment that the harness lives in, I feel confident that changing the harness should fix the problem.
 
1.4tdi wiring causing misfire

ive just had the weekend outside changing the wiring loom as suggested above..... in fact thats a lie ive just cleaned the connections and spayed some brake cleaner on the connection and put the same gasket back on as well and hey presto its sorted the problem thanks guys......
 
erratic starting/ non starting

could this problem be my erratic starting when mid warm ( but not always)?
also garry how do yuo get the air box out of the way or can iy be done without moving it?
Paul
 
Paul,

Im not really sure whether this could be your problem have you had the fault codes scan?

My problem could be made to go away for in one case 70 odd mile trip by cleaning the connector on the right hand side of the head (requires removal of no parts whatsoever its the round connector easily accessible.

Its just a bayonet style fitting. This must have dropped the resistance in the cable low enough for it to continue to work by cleaning the pins. However this problem kept reapearing getting worse and worse to the point i couldnt make it go away. So I removed the rocker cover and as I had bought a new harness anyway just swopped it.

As hamilton has just suggested I think he cleaned the connector under the cam cover too and this also seems to have fixed the problem for him. In my case i've been error free for 7000 miles now. It must be noted that my problem was not a starting issue but a missfire. This brought the ABS, and ESR light coupled with the beep and the yellow warning triangle on the dash. And the car was running on 2 cylinder, lumpy as hell undriveable. The car would start then could be 2 or three miles into journey would start to miss, could have been related to temperature.

I've not been following your starting issue but if you have any fault codes similar to those I described its well worth just changing for £35 in my opinion while you are in there. I would suggest cleaning that connector first see if it helps.

To get the cabin inlet out of the way with ease you need to remove the wiper arm then a short sharp tug at the edges of the cowelling at the base of the windscreen with the drains in will reveal two fasteners pozi if i recall correct which secure the air inlet down from the top, be careful not to disturb your pipes to your washer jets, if in doubt disconnect them but i did it without. To the right hand side of the inlet, again if i remember correctly, there are four nuts on studs that hold it to the bulkhead.then it should come away.

Then the cam cover is the bolts down to the top, the one at the back in the middle is a swine to get to. Cos the inlet casting is in the way so youll need a knuckle to get at it.

Youll then see the injector loom bathed in oil feeding each of the pump injectors, removal is then obvious.

Hope this helps.

Gary
 
Excellent advice, I experienced a misfire on my 1.4 Tdi and had a failed No1 injector diagnosed. With an estimated cost to repair of £870 I decided to follow the advice above and replace the injector wiring harness. Result one very sweet running, better than it has for a long time, Tdi engine.
I did however make the mistake of replacing the cam cover gasket and bad oil leak resulted on the rear RH corner of the engine. Purchased a new gasket expecting I had damaged the previous during fitting. However I found no problems with my work and the locating grove for the seal in the cam cover full of oil. On closer inspection I noticed that the cam cover has two locating notches for the seal at approximately 30 degrees up both sides of the cam bearing cap arches. The replacement seal has a single locating protrusion at the top of the arches. The locating holes in the cam cover were allowing the oil to enter the groove and hence the leak.
Problem was fixed by trimming of the unnecessary locating protrusions off the seal, one at each end. I sealed the four locating notches on the cam cover with liquid gasket being very careful to remove all excess. OK I bodged it but the problem is now solved. My advice is, as above, stick with the old gasket if it is not leaking.
 
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