The V8 Owners Forum -

Welcome advice on what appears to be an over fuelling issue. 3.9 Efi Hotwire, engine fires and will run with throttle and revs nicely but lots of white exhaust smoke.

I have replaced the ignition system with known good parts, together with the AFM and fuel pressure regulator.

What is interesting it still starts and runs with throttle when the fuel pump relay is pulled and pump not working. Must be pulling fuel through.

Could it be injector(s) sticking open, how can I check in situ.

Thanks

White smoke isn't over fuelling. That would be black smoke.

Sure it's not steam?

Or a wild-card - brake fluid getting into the intake via the vac hose from the servo?

Chris.

Thanks, definitely over fuelling as you can smell it and it quickly finds it's way into the oil, so I changed the oil.

Not steam, definitely co2 as filled the garage. It is not burnt oil either. Plug foul up with petrol.

Welcome any advice, especially on how to check injectors incase some are stuck open.

Thanks

Hi
I think you have already found out that some are stuck open! The ones where the plugs are wet would be a good point to start looking. white smoke is either water or brake fluid, I would take a bet that the over fueling has partially hydro locked (well petrol locked) one or more cylinders and lifted head gasket. Oh just realized it's a bob tail, had it in any big puddles lately? maybe it is a case that you have hydro locked it and just happen to also have leaky injectors?
Best regards
Mike

Oops changed signature as different off-roader.

Water level hasn't changed and no milk appearing anywhere, just fuel smell and a sump filling up so hopefully fingers crossed I've not blown the head gasket.

I need the test regime for the injectors as I have lots of spares but idea if good or not. Can they be changed without pulling the plenum?

Have you reset the ecu
It could have picked up a sensor fault and gone int limp home mode

Simple enough
Disconnect battery for 30 seconds

Reconnect
Try again

When mine did this the fumes were terrible and eyes would water in the back garden with it running!


Eventually you have to find which sensor sent the wrong instruction or it will do it again


Ian

Big Orange wrote:Welcome advice on what appears to be an over fuelling issue. 3.9 Efi Hotwire, engine fires and will run with throttle and revs nicely but lots of white exhaust smoke.

I have replaced the ignition system with known good parts, together with the AFM and fuel pressure regulator.

What is interesting it still starts and runs with throttle when the fuel pump relay is pulled and pump not working. Must be pulling fuel through.

Could it be injector(s) sticking open, how can I check in situ.

Thanks

First thing you need to do is check just what is happening with the fuel pump - as it certainly can't 'pull fuel through' with the pump stopped when things are normal. But killing the pump on a running engine won't stop the engine instantly - it will run until the rails are empty. Which does take some time.

The most common reason for over fuelling is a failed coolant temperature sensor. This has a high resistance when cold and progressively goes lower as the coolant heats up. If it fails open circuit, the ECU thinks it is very cold and goes fully rich.

Easily checked - unplug it and measure the resistance of the sensor. I don't have the actual figure for your injection - but would expect it to be something like a couple of thousand ohms at ambient temp. A faulty one will give either no reading or a very high one.

An ECUMate could be helpful in these situations


https://www.youtube.com/watch?v=K0kSParKR5U


https://www.youtube.com/watch?v=GIJNe0lV2LY

Robrover wrote:An ECUMate could be helpful in these situations


https://www.youtube.com/watch?v=K0kSParKR5U


https://www.youtube.com/watch?v=GIJNe0lV2LY

I doubt it does anything a DVM and some basic skills can't. I also doubt it can check the actual ECU properly.

Or this:
http://alum.wpi.edu/~colinb/14cux_software.html

To test an injector, you can 'jerry rig' one with a working fuel pump / fuel rail, and some crude electronics to open it. Then spray some fuel out of it into a container. Have to be careful not to cause any sparks! And you have to figure out a suitable circuit to fire the injector. I have only done it on the previous fuel injection system so I don't know the specifics for the hotwire.

Chris.

DaveEFI wrote:

Big Orange wrote:
What is interesting it still starts and runs with throttle when the fuel pump relay is pulled and pump not working. Must be pulling fuel through.

First thing you need to do is check just what is happening with the fuel pump - as it certainly can't 'pull fuel through' with the pump stopped when things are normal. But killing the pump on a running engine won't stop the engine instantly - it will run until the rails are empty. Which does take some time.

Hello Orange, Yes indeed it can 'pull through' as you put it! Running without the pump is a feature occasionally seen under certain conditions by RV8 Efi owners, even on a 'normal' engine.

Let's examine how this can happen?

Efi Engine Runs Without Fuel Pump

# For an RV8 Efi to run without the pump, there has to be a manifold vacuum and obviously, no amount of vacuum could jam the injectors open, so, clearly the ECU also has to be active, plus, the fuel pressure created by manifold vacuum must be sufficient to cause this effect.

# With the feed line (or even the return fuel line, dangling in fuel) still connected to the petrol supply, the manifold depression at idle is at its (normal) highest (minus10 psi approx).

# Normal atmospheric pressure (15psi approx) inside the tank combines with the manifold depression to give a total fuel line pressure of 25 psi approx).

# This is sufficient to push petrol through the pump, uphill to the filter and uphill again into the fuel rail.

# Thus, the difference between manifold depression and atmospheric pressure allows the injectors to function, admittedly at fairly low overall pressure, but sufficient to sustain a very low torque combustion process at idle speed rpm.

# The engine will continue to run as described until it runs out of fuel, or the ignition is switched off.

# The fuel rail remain full, all the time.

# Yes! several if not many owners have come across this phenomenon, even at first, I could not get my head around what owners were describing/confirming, but the more I thought it through, the more this tangible explanation emerged.

# Expressed another way! With fuel pump disabled the engine runs on because it is SUCKING up fuel with the normal depression seen at the intake manifold at idle speed in sufficient volume to fill the fuel rail and keep the engine ticking over due to the normal function of the injectors.

# In reality, it is a mirage, because the system was never designed to run as described and is merely a function of someone perversely pulling out a relay to see what happens.

So it is not impossible! Your genuine observation is exactly as described.

If you want to test the function some more, let the engine run as described and see how long it will run for without booting the throttle and with the ignition remaining 'on' (be sensible - not until the tank is empty!).

Your feedback would be appreciated.

Read more about this phenomenon from here:

http://www.vintagemodelairplane.com/pag ... ump01.html

Ramon, are you absolutely sure of that 25 psi fuel pressure with no pump?

Thanks Ramon,

Very interesting and I can report it will not tick over unaided by the throttle but as it's in the garage I cannot hang around without suffering from c02 poisoning. I have revved it and achieved a good 5 mins without having to evacuate.
I have changed the temp sensor, have to say the britpart one would not even fit properly so took one from a known good engine.

Can I check the injectors in situ although I do have a spare ecu to try.

Thanks

Big Orange wrote:Very interesting and I can report it will not tick over unaided by the throttle but as it's in the garage I cannot hang around without suffering from c02 poisoning.

Orange can you clarify this?

The statement confuses me if the engine will not tick over - otherwise you could stay in the garage with no ill effects, forever???????

I don't know how the injectors could be tested (for squirting) in situ but they can be tested electrically in situ with a multimeter .

Check out this archive for the 'fuel injector and power resistor' section

http://www.vintagemodelairplane.com/pag ... nts01.html

AFM is a good culpret for over fueling- its output goes higher than it should, so the ECU thinks the car needs more fuel. You can do a basic test with a test meter. This came from Mark Adams of tornado systems origionally:

Most airflow meter faults will cause the engine to run excessively rich. However if the airflow meter remains connected whilst defective then the vehicle will probably not run. In most cases the output from a defective airflow meter will be in the range 2.0-2.5 Volts, which is a viable value. This represents a moderate load and will cause heavy over-fuelling without setting a fault code.

Testing is performed in the following manner. Peel back the rubber boot on the airflow meter connector and leave it plugged in to the airflow meter. Set up the digital multimeter to read voltage. Insert the negative probe into the Red/Black wire (sensor ground), and the positive into the Blue/Green wire (Airflow signal).

Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts after the initial "warm up" spike. Most defective airflow meters will overshoot to 0.8 Volts or higher, and take at least 2 seconds to come down to the correct voltage.

As for Diagnostics the ECUMate is good for a hand held text display of the sensor data or fault codes, or there is the RoverGauge PC based software (its free)and if you do a google search you will find plenty on it. Hardware wise its needs an interface cable that costs £35 on Ebay.