Difference between revisions of "V6 Cold starting issues"

Revision as of 21:17, 22 May 2009

V6 Cold starting issues

Background

On occasion, my car would struggle to start from cold. It always fired up after 3-30 seconds of cranking whilst opening the throttle, depending on the weather. After checking the plugs, wiring to sensors, etc, I had the thought that one or more of the injectors was failing to shut off completely, allowing fuel to dribble into the combustion chamber overnight.

It seemed to do this more during the colder weather.

Upon firing up, the car would misfire on 1/2 cylinders for a handful of seconds, before sorting itself out and running without any issues.

I isolated the problem to leaking injectors by removing the fuse from the engine-bay fuse box for the fuel pump, whilst the engine was running on my drive, and allowing the engine to stall from a lack of fuel pressure. The removal of this pressure stopped fuel from weeping from any of the injectors, and the car always fired up first turn of the key the next day. If your car has this problem, and it is rectified by removing the fuse at night, then it's probable that you are also suffering from one or more leaky injectors.

Over time, the struggle to start will end up contaminating the catalytic converter with unburnt fuel, and will eventually poison it to the extent where it can no longer work.

The solution is to remove the fuel injectors, and have them ultrasonically cleaned.

The company I used offer a discount to all Gold members on reconditioned injectors, and they may be interested in buying your old injectors back after you've done the job, reducing the overall cost. If you want your injectors ultrasonically cleaned, they also offer a discount on this work. Please see the Gold members discount forum for full details.

Method

Everything noted here was done by me on a 1999 mk2. Depending on your model year, you may find differences between what I've written here, and your actual car. Please see the notes at the bottom of the article for possible injector differences between model years if you plan on buying reconditioned ones rather than having your own cleaned.

It's a fair old job to get at the injectors, as the inlet manifold has to be removed. Because of this, I opted to change the spark plugs and HT leads at the same time, though it may also be prudent to clean the secondaries out whilst you're at it.

I'd hoped to photograph re-assembly, so I could provide a thorough walk-through for you, but working at -5°C meant my photographs were useless because of condensation on the lens. Apologies. There is, however, a detailed guide on removing the manifold here: UIM & LIM Removal And Cleaning

A short list of what I did:-

Start the engine. Remove the fuse from the fuel pump to allow the engine to stall, removing fuel pressure.

Upper inlet manifold and associated ancillaries

Remove the plastic cover from the front of the engine. It is held in place by 3 bolts, and covers the water pump drive belt, and the IMRC unit.

Disconnect the plastic intake pipe from the throttle body, and from the MAF sensor. There was a small plastic pipe fitted on the side nearest the front of the car, which can be pulled out. The pipe leading off to the air bypass valve, located at the rear of the inlet manifold, should be removed. These hoses can now be moved out of the way, underneath the throttle cable(s) toward the rear of the engine. I didn't have to remove/disturb the MAF or air filter assembly.

Next, the throttle cables. Rotate the arm on the throttle body so the throttle is open. This removes tension from the cable(s), allowing them to be unclipped. There will be a secondary cable if your car has cruise control. The one just unclips, the second has a metal cover, which needs sliding out of the way to unclip the plastic end of the cable. Don't lose the metal cover! There are three bolts securing the metal bracket to the manifold. Note that one is slightly shorter than the others. Once unbolted, the bracket and cables can be moved toward the bulkhead on the - UK - passenger side.

Whilst in that area, now disconnect the wiring plug from the throttle position sensor on the throttle body.

Remove the 2 vacuum pipes from the top of the inlet manifold. One feeds the brake servo, the other is used(I think) for the vacuum controlling cabin heater controls. These are brittle, and prone to snapping. A wide screwdriver should help here.

Unbolt the EGR valve - this is on the right-hand side of the manifold, standing in front of the car. The EGR valve will only move away slightly from the manifold, due to the metal pipe at the base of it. You will need to either replace the gasket, or use instant gasket sealant when reassembling.

Finally, there is a black plastic block on the rear of the manifold. There are two bolts securing this. Unbolt them, and push the block out of the way.

All that is left now is to unbolt the 6 bolts on top of the inlet manifold. As always, start unbolting at the outside, undoing opposing corners. Once the tension has been removed, unbolt the two central bolts. With these undone, the manifold and throttle body should pull away from the engine. Remove, and store somewhere clean.

It is sensible to now remove the gaskets from the lower intake manifold, and cover the inlets with some packing tape to prevent anything falling in.

Fuel injectors

Remove the wiring to the fuel injectors. Depending on model year, there may be spring clips securing the plugs to the injectors(I think this applies to late mk1 through to '99 cars), later ones have a larger cream outer piece of plastic securing the clips to the injectors. The black plugs inside these are quite brittle, so take care not to damage them.

Once undone, the wiring can be pulled upwards. Do the same for the other bank of cylinders.

Next is the fuel rail. Haynes suggests removing the fuel hoses, but this requires a special tool, or making a substitute. This is not necessary, as the rail can be moved out of the way to enable access to all 6 injectors. There are 4 bolts securing this to the engine - three underneath the wiring, and another on the side nearest the throttle body. Remove these, and with a screwdriver handle, gently lever between the fuel rail and the lower intake manifold. Don't use anything sharp, as you'll risk damaging the mating surface where the manifold sits. Old 'O' rings tend to swell with age, making a very snug fit between the fuel rail and the injectors. I'd apply pressure to one side, then the other, and keep rotating until you feel it start to give.

With that out of the way, the injectors can be removed and sent for cleaning. Again, then may be a very snug fit. If you can't remove them by hand, use a pair of pliers, taking care not to damage the electrical contacts or anywhere near the 'O' rings. You won't need much pressure on the injectors themselves, the force should be primarily applied to pulling the injectors out rather than gripping them tightly.

Reassembly is the reverse of disassembly. Clean injectors should now give a better spray of fuel, yielding a better burn. This will help the engine make optimum power, whilst using as little fuel as possible to do so. Injector sealing should be as good as new, resulting in no fuel leakage overnight, which should aid starting.

Apply either a drop of engine oil, or a smear of silicon grease, to the new 'O' rings on the injectors prior to reassembly. This will help them locate, and reduce any damage from fitting.

I suggest once the clean injectors are fitted, and the fuel rail secured into place with the electrical connectors pulled away, priming the fuel pump a couple of times and inspecting thoroughly for leaks. If all looks good, leave it for 10-15 minutes, then re-prime the pump and check again. Once the inlet manifold is on, and everything connected, start the car. If any leaks are found, or the smell of petrol is extreme, remove the fuse to the fuel pump and go over your work.

Notes

1. If you plan on ordering a set of reconditioned injectors, take note that there are at least 3 different types. Early mk1s had black injectors. Later mk1s through to some mk2s had a beige type, with oblong electrical connectors using a spring clip to secure the power connector. Later mk2s used beige injectors(not including the ST200), which look very similar but use a different power plug. This type has two locating lugs on the right-hand side of the power connector, with a slightly rounded oblong socket.

2. It would be wise to replace all disturbed gaskets. Personally, I chose to clean the gaskets between the lower and upper intake manifolds. I also used instant gasket on the EGR valve mating faces. All mating faces should be thoroughly cleaned before reassembling.

3. Check EVERYTHING at least twice before attempting to restart the car. Leaking fuel can be disastrous. Keep a fire extinguisher handy, or at the very least a couple of bottles of water.

Submitted by Rich. Please let me know if you find anything inaccurate.