Over fuelling sensor connection check

[Philpooma 30]

I have a final challenge left to overcome when starting my newly rebuilt engine, I have an over-fuelling issue.

I have tested the injectors with the rail removed from the engine and all is well, the injectors have been re checked on a test rig and they perform 100% as they should. It seems that when they are installed back into the head the over fuelling issue appears.

 

I’m going to re check this morning with the injectors out of the car and then individually earth the injectors to check that the earth coil has not broken down on any of the injectors.

 

I have read on this forum about the ECU coolant sensor being connected in the wrong place, causing an over fuelling issue, can I ask that someone in “the know” takes a look at the attached image and confirms that these 3 connections below the dizzy are correct please?

 

I have added a photo of my injector test set up, so that I can see what the injectors are doing, looks very Heath Robinson, but does the job.

[jackherer 543]

The blue plug on the blue sensor is correct, that's the ECU coolant sensor and plug. The other two are just for the dash gauges.

 

Unplug the blue connector and measure the resistance of the sensor with a multimeter. Also check the terminals are correctly seated in the plug, they can be pushed back so they don't make contact.

[Philpooma 30]

6 hours ago, jackherer said:

The blue plug on the blue sensor is correct, that's the ECU coolant sensor and plug. The other two are just for the dash gauges.

 

Unplug the blue connector and measure the resistance of the sensor with a multimeter. Also check the terminals are correctly seated in the plug, they can be pushed back so they don't make contact.

Thanks for the reply, just out of interest, how do you measure the resistance of the sensor please?

I’m assuming you cant put the multimeter on the sensor connections as it wont have any power, and I wont be able tk measure the resistance of the sensor using the plug connections.

This is probably a stupid question, but I’m still learning with regards to automotive electronics 

[jackherer 543]

It doesn't need power to measure the resistance so you do need to unplug it.

 

Also leaving it connected would lead to a false reading because you'd be measuring the ECUs internal components as well as the sensor.

 

So unplug the connector and measure the resistance directly on the sensor itself.

 

The resistance obviously depends on temperature, this table shows the sort of numbers you're looking for, it doesn't need to be exactly the same as the table, just in the ball park.

 

[Philpooma 30]

I tested the injectors individually “outside” of the cylinder head. They all seem to work fine, I also earthed the injectors and re tested and got the same results. So at the moment it appears that the injectors over fuel the engine when they are fitted into the ports, but not when they are outside.......does that make any sense to anyone?

 

I’m a little stuck with this now, not quite sure what to test or do next 

[Philpooma 30]

3 minutes ago, jackherer said:

It doesn't need power to measure the resistance so you do need to unplug it.

 

Also leaving it connected would lead to a false reading because you'd be measuring the ECUs internal components as well as the sensor.

 

So unplug the connector and measure the resistance directly on the sensor itself.

 

The resistance obviously depends on temperature, this table shows the sort of numbers you're looking for, it doesn't need to be exactly the same as the table, just in the ball park.

 

Thanks Kieran, I’ll check that now.

I had started the other post above before seeing your reply. I’ll report back.

Would a problem with this sensor cause the engine to run rich as opposed to big over fuelling running on 3 cylinders?

[Philpooma 30]

Just as an additional question, I believe that its No.1 cylinder (timing end of engine) that is the problem.

If I use the multimeter on the injector feeds when the engine is being cranked, do you know what reading I should be seeing?

This would be good to know so that I can see if I have an issue with that particular electrical feed 

[Philpooma 30]

26 minutes ago, jackherer said:

It doesn't need power to measure the resistance so you do need to unplug it.

 

Also leaving it connected would lead to a false reading because you'd be measuring the ECUs internal components as well as the sensor.

 

So unplug the connector and measure the resistance directly on the sensor itself.

 

The resistance obviously depends on temperature, this table shows the sort of numbers you're looking for, it doesn't need to be exactly the same as the table, just in the ball park.

 

OK Kieran, I have just tested the resistance of the Blue ECU coolant sensor and (although its tricky to get the multimeter prongs onto the sensor posts) I didnt get a reading at all, just Zero.

I’m assuming that this means the sensor is dead?

[jackherer 543]

Yes as long as your multimeter works your coolant temp sensor is dead.

 

With what is effectively infinitely high resistance it will run at the cooler end of the range, i.e. -40c!

 

And that will result in massive over-fuelling if the ambient temperature isn't actually -40c.

[Philpooma 30]

I’m sorry Kieran, I just need to check something re the Multimeter.

The temp is around 20oc at the moment in the garage, so the reading I’m looking for is 2.5 ohms or 2,500 ohms?

 

The setting on my multimeter is as shown below, is this correct (I know this is amateur night, sorry)

[Philpooma 30]

I’m sorry Kieran, I just need to check something re the Multimeter.

The temp is around 20oc at the moment in the garage, so the reading I’m looking for is 2.5 ohms or 2,500 ohms?

 

The setting on my multimeter is as shown below, is this correct (I know this is amateur night, sorry)

[jackherer 543]

It's 2500 ohms at 20c.

 

So you need it on the 20k setting.

 

Check it works first by touching the probes together and making sure it reads close to 0.

[Philpooma 30]

6 minutes ago, jackherer said:

It's 2500 ohms at 20c.

 

So you need it on the 20k setting.

 

Check it works first by touching the probes together and making sure it reads close to 0.

Thanks for that, I was clearly using the wrong setting on the meter.

So retesting using the 20k setting I got a reading of 2.43.

So looks like my sensor is in the right ball park?

I was so hoping that this was going to be the smoking gun.

 

Looks like its back to the drawing board, thanks very much for your help Kieran 

[jackherer 543]

Yes that is pretty much perfect then.

 

Check the pins in the temp sensor plug haven't been pushed back into the blue plastic housing.

 

If that's OK then have a look at the air flow meter.

[Philpooma 30]

4 minutes ago, jackherer said:

Yes that is pretty much perfect then.

 

Check the pins in the temp sensor plug haven't been pushed back into the blue plastic housing.

 

If that's OK then have a look at the air flow meter.

Sorry to ask, but what am I looking for with the AFM?

[jackherer 543]

It's a bit more complicated to test!

 

This article is useful: http://web.archive.org/web/20150329103701/http://www.the944.com/afm.htm

 

And it's discussed in the context of a 205 GTi here: https://www.205gtidrivers.com/forums/topic/158929-afm-identification-and-testing/

[Philpooma 30]

15 minutes ago, jackherer said:

It's a bit more complicated to test!

 

This article is useful: http://web.archive.org/web/20150329103701/http://www.the944.com/afm.htm

 

And it's discussed in the context of a 205 GTi here: https://www.205gtidrivers.com/forums/topic/158929-afm-identification-and-testing/

Thanks very much,  I really appreciate your help 

[welshpug 1,621]

how are you measuring this over fuelling?

[Philpooma 30]

8 hours ago, welshpug said:

how are you measuring this over fuelling?

When I first started the engine, it ran perfectly for 5 mins, then it started to run unevenly (3 cylinders) and smelt of petrol. We then noticed petrol dripping out of the exhaust joint at the back of the car, at that point we stopped the engine.

So somehow way too much fuel is getting into the engine.

As you will see in the summary above, when the injectors and fuel rail are out of the engine, the injectors seem to operate normally.

The injectors were refurbished before being fitted into the engine and last week were out back in the test unit and cycled, they all ran perfectly.

 

Currently I’m stumped 

[PhilNW 40]

Does the same happen every time you start it?  i.e. as it warms up it starts to misfire but ok when cold?

 

Does it start immediately or does it need a bit of churning?

 

The petrol smell  is probably unburnt fuel (from the misfiring cylinder)  being ejected down the exhaust. Dont think you will have neat petrol at the end of the exhaust just condensation ( or god forbid water from a leaking head gasket or similar) 

 

The misfire may be a fouled plug ,  can you check, you may find a wet plug.

 

Are they the correct grade of plug?

 

It may be something electrical i.e a plug or plug lead  failing when hot. 

 

Dont think the injectors are over-fuelling if they are OK injecting against atmospheric pressure (when tested) doubt they will over fuelling against a cylinder pressure of over 100 psi

 

 

Edited August 8, 2020 by PhilNW

[Philpooma 30]

51 minutes ago, PhilNW said:

Does the same happen every time you start it?  i.e. as it warms up it starts to misfire but ok when cold?

 

Does it start immediately or does it need a bit of churning?

 

The petrol smell  is probably unburnt fuel (from the misfiring cylinder)  being ejected down the exhaust. Dont think you will have neat petrol at the end of the exhaust just condensation ( or god forbid water from a leaking head gasket or similar) 

 

The misfire may be a fouled plug ,  can you check, you may find a wet plug.

 

Are they the correct grade of plug?

 

It may be something electrical i.e a plug or plug lead  failing when hot. 

 

Dont think the injectors are over-fuelling if they are OK injecting against atmospheric pressure (when tested) doubt they will over fuelling against a cylinder pressure of over 100 psi

 

 

Thanks for the reply Phil.

Last time I started it, it started immediately and ran on three cylinders, so I killed the ignition. There was some liquid dripping from the rear silencer joint which smelt of petrol, so thats why I’m assuming its over fuelling.

 

When I removed the injector rail, No.1 cylinder spat out some petrol, so pretty sure my issue is with No.1 cylinder

Initially we had a weak spark with No.1, we have since replaced the HT leads and the plugs and we have good sparks on all leads and plugs.

 

I suppose its possible that it could be residual fuel in the cylinder and I may be assuming (incorrectly) that its new fuel. However, I have removed the spark plugs and left the cylinders to vent (in a dust and dirt free garage).
 

I also as a precaution dropped the running in oil and replaced with fresh oil. The oil did smell of petrol but had no traces of water in it.

 

Are there any situations where the injectors could pump large amounts of fuel into the engine at low revs?

Thanks for your interest and comments.

I’ll report back when I have tried the engine again 

I think the next step is to check all cylinders are free of fuel, re check the spark plugs for a good spark, make sure they are Clean and try to start the engine again.

[PhilNW 40]

Quick and dirty way to check which cylinder is the problem is to take off the plug leads one at a time and see what effect it has on the misfire.  Best way is to stop and start engine between cylinders so you dont get any nasty shocks from the plug leads with engine running. No change in misfire means that cylinder is the problem cylinder, increase in misfire means that cylinder is good.

 

Place a screwdriver to the injector while running and the other end to your ear and listen for the consistency in the ticking noise  (the opening and closing) of the injector, might give a clue.

 

The variation in length of the injector pulse (the tick) which controls the volume of fuel injected is basically controlled by the AFM and the temperature sensor.

 

If the injectors have been tested cant see a good reason for overfuelling on one cylinder. Do you have a Gunson colourtune plug (the one which lets you see the colour of the flame in the cylinder) it should give a quick and dirty way of seeing lean or rich fuel mixture. 

 

EDIT - the petrol smell in the oil is probably the misfire pushing raw fuel down the cylinder walls past the pistons rings. Careful it may wash oil from the walls causing premature  wear. 

 

Edited August 8, 2020 by PhilNW

[welshpug 1,621]

don't need to stop and start, use a pair of insulated grips.

 

as for the injectors running against pressure, they don't unless it is a boosted engine, they will be under a vacuum with the throttle closed, about half a bar at the most, the vacuum reference tube to the pressure regulator compensates for this.

 

if the car has not been run up to temperature and given a decent drive the exhaust can be full of condensation which will smell of petrol.

 

 

I would start with a compression test, a fresh set of plugs and have the injectors refurbished/cleaned.

[Zetec7 4]

3 hours ago, PhilNW said:

Does the same happen every time you start it?  i.e. as it warms up it starts to misfire but ok when cold?

 

Does it start immediately or does it need a bit of churning?

 

The petrol smell  is probably unburnt fuel (from the misfiring cylinder)  being ejected down the exhaust. Dont think you will have neat petrol at the end of the exhaust just condensation ( or god forbid water from a leaking head gasket or similar) 

 

The misfire may be a fouled plug ,  can you check, you may find a wet plug.

 

Are they the correct grade of plug?

 

It may be something electrical i.e a plug or plug lead  failing when hot. 

 

Dont think the injectors are over-fuelling if they are OK injecting against atmospheric pressure (when tested) doubt they will over fuelling against a cylinder pressure of over 100 psi

 

 

Its not a diesel, they are injecting into the inlet manifold that's usually vacuum unless wide open throttle 

[PhilNW 40]

My mistake - I was thinking diesel