wierd plug fouling condition

Ricky · 04-02-04, 06:54 PM

I am interested in comments from some of the boffins out there.

My 40 has been fouling plugs in a wierd way and I can't really work out why. The front pair are perfect and progressively the plugs go a nice biscuit colour to finally a black dry foul at the rear cylinders. The colouring is consistant from left to right banks and seems really odd.

The WOLF (V4) ECU has been set up properly and tuned - it is a group fire unlike the motec sequential system, the engine runs a victor jnr manifold with 4 barrel throttle body for simplicity and $$ savings until I can justify the quad stack system and plugs are NGK BPR6EFS.

Engine temp appears to be consistant on the gauge at about 80 degrees C

Any suggestions ??

Cheers,
RV

Kevin M · 04-02-04, 07:17 PM

This system has individual injectors taped into the manifold at the ports? If so, what is the routing of your fuel lines? Does it run down both sides from a common feed point? And, if so, is it richest at the feed end of the fuel lines?

Where I am going with this is, because it is a group fire system, it uses a lot of fuel at one time, if the lines are sized for a sequential system you may be getting less pressure as you go down the manifold. A fuel pressure gage inserted at a few key points will tell you if it is something like this.

Kevin

Ricky · 04-02-04, 08:51 PM

Correct, The injectors are inserted directly into welded bosses on the manifold ports.

The fuel rail is a continuous loop around the outer perimeter of the air cleaner - if that makes sense. Fuel is supplied at the front of the rail (front right cylinder of engine) loops around and returns to the pressure regulator also at the front left of the engine

-------->
| |------<
| |
|_|

(actually the regulator is burried in the right hand sill with the fuel pumps)

If there is a pressure loss I would think it would be at the left hand front cylinder which seems fine so I think presseure can be discounted.

Cheers,
RV

Kevin M · 04-02-04, 09:56 PM

OK, if it’s not fuel pressure, then it pretty much has to be pulse.

How is the wiring set up from the computer to the injectors? Is there any pattern in the wiring that corresponds to the front to back “layering”? We are looking for anything that could possibly cause the signal to the injectors to loose voltage through some source of resistance as we move toward the forward injectors. A check here would be to put a Voltmeter in the circuit at a front & rear injector and look for a voltage drop. (It will be small, most injectors are wide open at 5 volts or so, this won’t necessarily be easy to see).

Kevin

Kevin M · 04-02-04, 10:24 PM

Rick,

There is an easier way to test this. If the system is a batch fire, it should fire all of the injectors at the same time and with the same signal. That said, it should make no difference which lead is connected to which injector. Try removing the harness and reinstalling it backward. That is to say, connect what were the front cylinder connectors to the rear cylinders and connect what were the rear connectors to the front injectors, etc. Then see is the pattern on the plugs changes from one end of the motor to the other.

Kevin

Robert Logan · 04-04-04, 03:35 AM

Kevin / Rick,

It could be fuel pressure !!!

You might need to adjust the pressure regulator.

Best wishes,

Robert

Eric · 04-04-04, 10:17 AM

A pic might help. Another possibility is burning oil in those cylinders.?

DenisBedford · 04-06-04, 05:25 AM

Rick before you pull anything apart disconnect all vacumn lines from the manifold, throttle ,etc(PCV vac brake etc)and block all the openings and check any openings on the throttle body that may not have been blocked

Kevin M · 04-10-04, 09:51 AM

Rick,

Did you find or solve the problem? If so, please post a quick explanation. I am really curious on this one.

Thanks,

Kevin

Ricky · 04-13-04, 06:59 PM

I have been pretty flat out at work the last week so have not gone too far but the story so far....

1.Checked for vacuum leaks - no problems here.
2.Changed plugs - this was done regardless. I am not sure what was installed but will pull the plugs after a run on the weekend to see how things look and establish what the plugs are that were fitted before the retune.
3. Had the cold start set up altered once again the guy doing the ECU mapping believes the fouling was from the cold start. We shall see.......
4. Oil usage has been non existent even with track days. I kind of ruled this out as the plugs were dry fouling and not sticky gummy or wet.
5. I will check the fuel pressure and will fit an adjustable regulator. the present one is a preset unit supplied with the system.
6. I am still not happy with the low speed running (Idle - 2500rpm) the tune is not allowing a nice clean pull, it is a hesitant run until 2500 then goes like a blur from there.
7. I am going to get someone else to try and tune this damn thing. I see no reason why it can not run strong and clean from idle to the 6300 cutout.

Will keep you posted.
RV

flatchat(Chris) · 04-14-04, 06:50 PM

Sounds a bit like an intake manifold leak--try tightening the bolts -- an engine anyliser should pick this up
Good Luck! [img]/ubbthreads/images/graemlins/cool.gif[/img]

Adam C. · 04-15-04, 11:38 AM

[ QUOTE ]
what is the routing of your fuel lines?

[/ QUOTE ]

I think Kevin is on the right track. I think it is probably a system dynamics problem (sort of like water hammer), and less of a flow problem however. I bet if you make it so that the fuel rails are connected front and rear, like the OEM does, then the problem will greatly diminish.

Sorry about the crappy picture. It is all I had laying around.

Adam

Adam C. · 04-15-04, 11:44 AM

Sorry,

A vacuum leak between the intake and head face is also a very strong possibility. Were the manifold or heads ever milled?

Adam

Howard Jones · 04-15-04, 01:06 PM

Adam may be on to something with his milling question. I had a big ford,460, once that had a warped intake manifold. This resulted in two cylinders , the last two side by side on one head, fowling plugs. I replaced the intake gasket and right away the problem came back. In the end taking everything apart to crack check the head, intake , resulted in finding the warped intake. I believe it was cast bad from the begining. The engine ran okish and I wouldn't have found this problem if I wasn't doing a tune up and noticed the two different plugs readings.

You might want to really have a look at the intake to head surface for flatness. If a given cylinder goes super lean, 40-50 to 1 or more because of a leak then the fuel charge might not even burn resulting in a fowled plug. This might also be the cause of your low speed ruffness. Low engine speed\ high vacume would be the worst case for this if this is it. At a higher engine speed low vacume condition the entake charge might just fatten up enough to fire. Here's your higher rev power coming on.

That is all I can think of, except if you are going to tune the FI again check EACH cylinder fuel\air ratio. This is going to be hard with your exaust system. You might want to fit up some cheepo exaust manifolds with sensor bungs in each exaust port just for the setup of your FI system.

I hope this helps.

Ron Earp · 04-15-04, 03:03 PM

Check that leak using some WD40 or similar. Spray around the area and if you can detect a change is a number of things - vibration, sound, RPM, etc. then you've found it. If it is a leak that is not exposed to your spray it won't help you, but at least it is worth a shot.

Ricky · 04-24-04, 08:13 PM

The latest on this subject.

1) Sprayed with CRC around the manifold - no difference.

2) Changed the thermostat to a 91Deg C unit as the car was struggling to maintain a constant 80 deg water temp on the road (It is fine on a dyno)

3) I went into panic mode when someone mentioned possible warped manifold (no machining was done to heads or manifold)

4) Had one of those "Oh F*!$K It" days and ordered the stack manifold and throttle bodies. (The wife took this quite well actually!)

5) Replaced the coolant by pass piping from the back of the inlet manifold to the thermostat housing (Originally removed as the car was taking forever to get any form of temperature into it and figured that coolant bypassing the thermostat was just heating 20+ litres of radiator coolant instead of coolant in the block keeping the engine in cold running mode for too long) Reinstating this plumbing has removed the big change in temperature from thermostat open / close and was in hindsight probably tricking the computer into cold running mode / rich mixture setting in a cyclic fashion.

As a result I had a run at a the latest sprint round yesterday and found that when cold it was still a bit fluffy down low. Once temp was up to about 60 deg + it got better and better with no back firing or fluffiness.

I pulled the rear plugs and they are perfect.

Only problem now is that after doing 5 or 6 practice laps on the sprint circuit the ignition died when on the first timed run !! so now it is back to the drawing board to work that one out.

Many thanks to all for their input.

RV