Phil Silano

New problem this week, looks like an internal fuel leak as there is a strong smell of gas in the engine oil and gas consumption is excessive. Not to mention stalling at idle. Another indication is a failure to maintain fuel pressure in the injection lines after turning off the engine. The 34 psi indicated starts to bleed off immediately and quickly.

My initial thoughts are the cold start valve or a bad fuel injector.

Any other ideas out there or thoughts on how to narrow down the search?

Thanks.

joejoe

Perhaps a bad spark plug is not firing and washing a cylinder. That would be bad as it can really ruin a cylinder. Other is injector failed open and just dumps fuel all the time, same situation of washing cylinder and then into crank case. Check valve can also cause loss of pressure. this is cheap to change and if it hasn't been done it needs it. Hope this helps and am sure others will be here soon.

dr bob

Phil, what kinda car are we talking about here?

Phil Silano

It's an 83 928S. I should have mentioned that there is no evidence of fuel in the vacuum lines connected to the pressure regulators or damper.

dr bob

Regardless, you have a leaking injector. Fuel is washing the cylinder wall, taking the oil with it into the sump. DO NOT START THE ENGINE AGAIN UNTIL ITS FIXED. Besides the obvious issue with piston and cylinder scuffing with no oil, you have a serious risk of hydro locking the engine with fuel. Bends rods, breaks pistons when you try to start the engine.

Put a jumper in the fuel pump relay socket 30 to 87 for a minute, with spark plugs out. Sniff the cylinders to see which has gas in it. Might be more than one. Replace all the injectors, or at least have them cleaned and flow tested.

z driver 88t

Sounds like injector has failed open. Its been many years since I had to trouble shoot an injector. Generally they "click on" when you put 12V across the terminals. If you unplug them all and attach a 12V lead across the injector terminal see if you can hear a slight click, almost sounds like a relay, but softer. If one of them is permanently in the open position my guess is you will not hear that one click.

Nissans (where most of my experience is) tend to fail in the "injector closed" mode vs open, but I'm thinking the method to diagnose would be similar. I suppose if the seal has failed internally, you MIGHT still hear the bad injector click to fire and not be able to tell which one is bad, but its the easiest way to start.

Only alternative I can think of is to pull each one and physically run a fuel pump to the injector (You can drop a generic fuel pump into a bucket with a little bit of fuel and run a hose to one injector at a time and see if any allow fuel through with no current across the injector.

All this is backyard mechanic stuff we came up with while brainstorming working on old Z cars in the garage. I'm sure there are documented correct "injector test" procedures somewhere.

Phil Silano

Working on the troubleshooting this afternoon.

All Spark plugs are removed and no gross abnormalities noted. Cylinders 1-4 appear to be running slightly richer than 5-8.

Jumpered the fuel pump for several minutes with no apparent fuel or fuel odor from any cylinder. Using a stethoscope on each injector did not reveal any noticeable difference in sound. The loudest noise was coming from the cold start valve. That was the only one with a different tone.

Pulled the cold start valve and found no evidence of fuel in the tube leading from the valve into the intake. The increased flow noise may have been transmission from the fuel rails since the cold start valve is connected via a metal pipe while the injectors have some sound isolation via the rubber hoses.

Should note that although there is an odor of gas in the engine oil there does not appear to be any increase of liquid volume in the crankcase.

Running out of ideas here. Any other suggestions out there?

dr bob

There's a very short list of nine places where fuel can get to the oil. You'll know its injectors by sniffing cylinders, but you may need to rotate the engine to get the intake valves open under all the injectors. The fact that they click means they are moving, but is not an indication that they are closing. If they've not been cleaned in the last 75k miles or so, pull them and send them to Witchhunter or your other favorite service for cleaning and testing. You can pull a cold-start valve and test it with a 9V battery and pressure on it to verify both open and closed operation, as you might with the other injectors. The 9V battery is better than a 12V when you plan to leave the coil actuated for a while.

Phil Silano

I was about to rotate the cylinders when I decided to check one more thing first. The fact that cylinders 1-4 were running rich was just eating at me. I disconnected the "Y" pipe from the cold start valve and aux air valve to the back of the heads. Gas poured out of the right side. I think there is a spare valve in my parts bin but won't be able to verify that until next week. I'll update this post after the fix is verified.