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Discussion Starter #1 (Edited)
Fuel contaminated oil/extended cranking

Today whilst having my oil changed by a mechanic, it was observed that there was a strong odor of fuel in my oil and the oil seemed thin. I previously thought I had smelled exhaust/gas in my oil before changing it, and it dirtied quickly (Mobil 1 5w-30).

The car in question is a '93 Thunderbird SC 5 speed. Plugs/wires are basically new, Autolite & Motorcraft. I checked the fuel pressure regulator by observing the vac line for fuel with the engine off & on, none was found.

The car has a couple symptoms. Cranking time is slightly extended whether warm or cold, and during some warm restarts, the car will chug slightly before running and give a few puffs of black smoke (rich exhaust). There is also sometimes a slight smell of fuel in the air when starting warm or cold.

I am going to add Chevron Techron concentrate to the fuel tank as I think it could be dirty injectors leaking through after shutdown.

What are your thoughts on this problem? Thanks!
 

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I think you're on the right track with suspecting leaking injectors. Chevron's techron fuel system cleaner is the best stuff on the market from what a friend that works for a Siemens fuel injector rebuild facility told me. If I were you, I'd put in 2 large bottles of Techron in a full tank and then run it down to a quarter tank and see how it acts. Monitor your oil closely for fuel smell. I'd also suggest a switch to 10 W 30 for the summer. If that doesn't cure the fuel smell/thinning of the oil, replace the injectors.
 

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send a sample of the oil to blackstone labs and get an engine oil analysis done.

They will tell you everything about the motor.

The report is only 20 bucks and its money well spent.

JH
 

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Good suggestion Justin :)

On the topic of other means of fuel entering the crankcase... The only way that I'm aware of in an injected engine is leaking injectors. If the fuel was blowing by the rings and assuming you change your oil at around 3k miles, it would take a LONG time to thin the oil because the fuel would almost have to vaporize in the heat of the crankcase in that small an amount and the PCV system would suck the majority of it out.

My hypothesis is that you have injectors sticking open even after the engine is turned off dumping raw fuel into the cylinders in liquid form that is then running past the rings (also cleaning the oil off of your cylinder walls!!!) and contaminating the oil. I tend to be more paranoid than most people so take that into consideration when I say that were I to find fuel contaminated oil, I would replace the injectors immediately.
 

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Discussion Starter #6
As an update, I added the 12 oz Techron concentrate to 3/4 tank last night. Previously there would be small bumps which were detectable by placing my hands on steering wheel. With my solid rubber motor mounts, these bumps were fairly obvious. After driving 60 miles, I was able to notice a difference in the idle. These bumps were completely eliminated, under cold and warm engine conditions.

After another 40 or so miles, I then tried starting the motor from full temp after shutting down for 5, 10 and 20 minutes consecutively. Each time, the motor started up w/o chugging, and seemingly less crank time. These were night time temperatures however, so I will have to wait until warm weather returns here (65+) to observe any difference it has made in starting.

Obviously there was a problem with either carbon in the combustion chamber or dirty injectors cuasing ruff idle. Now to see if it was related to the starting, and if the Techron can clean well enough to eliminate it..
 

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Discussion Starter #7
Ok I have finished the tank of fuel cleaner and my starting situation has not improved.

It seems the starting problem is increasing too. Cold starting time is up slightly, warm starting is about the same. It does seem to take longer when cold than it does warm, and I've noticed when the engine is up to full temp crank time is almost normal for up to about 30 minutes after shutdown.

The new oil doesn't show indication of fuel contamination yet, but it only has a couple hundred miles on it or so.

I don't really know what else to chech for this. The lack of any other symptoms is making it difficult.
 

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Get or have someone put a pressure gauge on the fuel rail and monitor the pressure after the engine is shut down. It should hold pressure for at least 15-20 minutes. If it drops faster, then you have a fuel leak, which means either (assuming your not leaving a puddle of gas) 1 or more injectors are leaking and/or the check valve in the fuel pump is bleeding back. Since you had gas in the oil you could probably lean toward a injector problem rather than the pump.
 

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Discussion Starter #9
I have another vehicle in which the check valve for the fuel pump had failed, so I originally suspected it in this case. However, I was told by others that Ford does not use a fuel pump check valve?

Also, my knowledge of the fuel system is limited. If its normal for pressure to bleed off after 20 or so minutes, what precisely about the pressure bleeding off in less time causes hard starting? Does the fuel accumulate instead of vaporizing, or is it something different entirely?

Lastly, would an injector sticking open always cause a noticeable rich condition when running? I do not currently have this.

Thanks for the help!
 

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I know in diesel engines, fuel/oil contamination can be caused by bad piston rings. I'm a Coast Guard mechanic, and a generator at one of our lighthouses had 75% fuel/ oil dillution. It also sounded like complete crap while it was running (we tried to run it to the ground so we would be allowed to rebuild it or get a new one). The problem turned out to be completly shot piston rings. We thought it was injectors initially, but after we replaced them all about 3 times, and still had 75% dillution, it became apparent we were barking up the wrong tree. Lets just hope that's not the problem with your car!!
 

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Discussion Starter #11
Thanks for responding MadCanadian.

I had considered this also, although I don't seem to have any problem with compression, at least by the power it has. It does run well, and I never get abnormal smoke from the tailpipes, except after that occasional warm restart.

Come to think of it, the engine seems to have less trouble during warm restart after the injector cleaner even though cold crank time has increased. Maybe I'll try another tankfull..

Still wondering about that check valve..
 

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I'd say the injectors are sticking open or not closing all the way. I know a guy that has an '89 Mustang 5.0 5spd and his stock injectors were stuck wide open. When he'd start the car cold it looked like a mesquito fogger. His engine was like an oil factory cause the oil level kept getting higher without adding oil. His problem was bad enough he could drain his oil and light it on fire (almost more flamable than deisel). He sold the engine for a 351 stroker (427 stroked) and the guy that bought it put new injectors and it was fine.

Clay
 
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