Hi all

Just when I thought my problems were over I ran into another issue, and this one has me stumped

She was running just fine, starting very easily and not missing a beat (apart from no power, which I am convinced is vacuum lines) I got back home after a 10 km drive to see family (20 there and back) about 30 mins later my dad wanted to drive her, she wouldn't start... And she has been like this since. I had disconnected the CTS and checked the reading after I got back. I tried again the next morning and got a few coughs and a very rough run, when I opened the throttle a little she shook a lot and backfired rather loudly. I noticed that I had left the CTS off, I put it back on and it made no differnece . I have since checked the ohm reading at the ECU (pin 5 and 19) and she is reading about 3,17 when the multi-meter is on the 20k scale (I assume this is the "10's scale"). This seems about right and and the reading does vary with temp as it should (down to about 0.19 when hot on the same scale). I also checked the output fuel regulator and it breaks at about 23 psi, which it was doing before. My question is what should I check next, what are the possible reasons for this?

One last thing I might mention is that when I disconnect the fuel line at the filter, after running the pump, it no longer sprays everywhere like it used to... the pump sounds normal and I can hear fuel moving through the output regulator (which I have checked)... I have also tried restricting the output flow of fuel to increase the pressure, this doesn't make any difference...

Any advice is much appreciated.

 

I personally was thinking fuel as I was reading along, then you mentioned fuel(not spraying). that is a lack of pressure. Check valve for sure, but there are ways to bypass that. Mine went bad a couple weeks ago. As stated elsewhere on this forum site. Put it in gear(R or D) and turn the key to the start position and hold it for a few seconds, put it back in P or N and try starting. That primes the fuel system.
But the backfiring? thats a lack of either fuel pressure or a lack of spark.
Spark plugs, wires, cap, rotor? None of these would cause the loss of pressure that you described though.
My 2 cents!

 

Many thanks Amaezing, however I think that the V12 is wired differently and this test only applies to the straight six, I might be wrong however... I have also had the pump hot-wired so that it only runs in position 2 and 3 ("on" and "crank"). I am also thinking a pressure issue, possibly pump related... I am not sure if a pump can fail in this manner? the lines at the fuel rail do seem softer than usual, but increasing the pressure made no difference... (I did this by putting a slight pressure from a pump into the outlet regulator).

 

Yep, your probably correct. I am not familiar with the V12

 

I would check the 'deadhead' output pressure of the fuel pump. That is, unregulated fuel pressure.

Remove the supply line (at RH side of the fuel rail) and attach your pressure gauge directly to it and then operate the fuel pump. You want to see 75 psi or so. Of course, with everything hooked up, this is regulated way down.

I suspect that your fuel pump is operational but weak...or you have a badly plugged filter

Cheers
DD

 

Many thanks Doug and Amaezing, I'll check those items today and report back.

 

Right, I have found a problem, the one-way valve was faulty, hence the low fuel pressure when I took the filter in the boot out, the one-way outlet was sticky, as a result, most of the fuel pressure was going back to the tanks... However, she still wont start... Is it possible that she may be flooded from all the cranking? I am told the the HE does not like being flooded... When cranking she merely coughs on a few cylinders... Seemingly the same ones... Opening the throttle has very little effect... Not having a pressure gauge (yes I know) to check the pump pressure makes things difficult... However the lines are no longer soft like they used to be.

Any other suggestions?

I'm getting desperate to have her running again...

 

Hi all

Today I pulled the rail off, fulled it with fuel, pressurized it (about 22 psi) disconnected the fuel pump, connected all the injectors to the loom (which was connected to the car) and cranked... Fuel, they all fired.

Then I pulled a plug out, seemed fairly clean, carbon right around though. I also checked for spark at this lead, and there was a very strong blue spark at the lead...

She is still only coughing on a few cylinders...

Any further suggestions out there

 

Looks like Doug said it should be 75 psi. Did I read that right? If so. There's the problem. I can almost guarantee its fuel, since you have good spark.
There is a way to cheat the flood if it is flooded with starting fluid. Remove plugs spray a bit of starting fluid in hole reinstall plug to trap fluid. Repeat on all cylinders. Then start it. Do not do in diesel motors but I've always had luck cleaning this way.
My 2 cents. I'm sure others will disagree or be scared, but I've done it many many times.

 

You've determined that all of the injectors are fundamentally operational, which is obviously a good thing.....but that alone doesn't prove they're operating correctly while the engine is running. But, for the moment, we'll assume (probably correctly) that they're OK.


Fuel pressure: can you clarify the 22 psi? Is this while cranking? With regulators in play?

You should have about 30-38 psi regulated pressure and, as mentioned earlier, about 75 psi raw pump pressure



Cheers
DD

 

Good.

You'll have to dig a bit deeper, I'm afraid....you still have 11 cylinders to go ! I know that pulling plugs on a V12 is not something done on a whim but pull at least a couple from each bank and see if they look the same as the one you already pulled.

How does the inside of the cap look? What about plug wires?

With the engine running go to the back of the car and listen to the exhaust. Is one side purring while the other sputtering? Or one side chuffing black smoke while the other is clean? You might be able to narrow things down a bit.

Cheers
DD

 

Good tip and it works

Only problem is that removing plugs on a V12 is a couple hour ordeal....or an entire afternoon it you're a first-timer. By the time you got everything buttoned back up the starting spray would have probably evaporated!

In the back of my mind I'm thinking the that ECU cuts off the injectors if it sees a cranking signal (taken from the starter circuit) together with a wide open throttle (taken from the throttle position sensor). This would obviously help clear flooded cylinders (like we used to do with carbureted engines)....but I can't find (at the moment) anything in writing to confirm my thoughts on the matter

Cheers
DD

 

Many thanks Doug and Amaezing

The trouble to start with is that she doesn't actually start and run, so I can't check the pipes, she did however run smoothly on both sides before she started playing up.

The pressure up to 38 psi? I know she is only 22 psi, is this possibly too low? She has run with this pressure all of the time...

I'll pull as many plugs as I can and see and check their condition, I may have just pulled the plug from one of the 'coughing' cylinders...

I also had an extra 'in-line' filter fitted, just before the regulators (even the lines are dirty) so I'll clean this one too.

I'm hoping it's either plugs, fuel or the pump...

I'll report back what pops up.

Thanks again for the help, I really appreciate it.

 

Right... Problem found... Carbon build-up in the dizzy...

First problem was the non-return valve, located just before after the filter... The little rubber (I assume) piston had "tumbled" and as a result wasn't delivering fuel pressure to the rail.

This was made worse by the carbon build-up in the dizzy.

At least that's what I think...

Happy driving