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Horrible, Mysterious Detonation

3K views 29 replies 5 participants last post by  fergawesome 
#1 · (Edited)
I purchased a 2001 Ford Taurus SE with the 3.0 12v V6 Vulcan, featuring sequential multi-point fuel injection and a returnless fuel system, last July.

From day one, I noticed slight detonation while running 87 octane. Some injector cleaner treatments and higher grade fuel eliminated the issue mostly, albeit it's progressively worsened. I'm now running 93 octane, and I persistently experience intermittent detonation. Eliminating:
-EGR valve (cleaned, but hardly dirty; not stuck)
-MAF sensor (cleaned and reading sufficiently)
-Vacuum leaks
-Exhaust leaks
-Failing PCV valve (new)
-Spark plugs (new)
-Wires (new)
-Ignition coil pack (firing all six cylinders strong)

and a couple alternatives that I do not recall, I'm bewildered.

1) She features a returnless fuel system. Bank 2 fuel rail incorporates a fuel pressure sensor; albeit it's disconnected from the wiring harness (the connector has been deleted from the wiring) and a feedback line to the EGR has been deleted as well. When I sought to read the fuel rail pressure with a scanner tool, the data stream for the sensor read 'not supported', suggesting that the PCM had been re programmed. Moreover, the fuel rail has a numeric identification, written in marker, much like that of standalone parts in scrap yards, but the former owner claims to have done any and all maintenance with the Ford dealership. Do returnless fuel systems not require a fuel rail pressure sensor in order to function, or to function properly, rather?

2) For the past two fill ups, when I reached a half tank, detonation was unbelievable. After topping off the tank and a couple minutes later, the detonation reduced and then ceased.

I put a flat-blade screwdriver to each of the injectors to conclude that they are all firing, and I have run some four injector cleaner treatments through the fuel tank since purchase of the vehicle. Moreover, I ran injector cleaner directly through the intake manifold into the cylinders to perhaps reduce the effect of carbon on increased compression.

I had access to a borescope recently, so I removed the spark plugs and inspected the pistons. Pistons in cylinders 4-6 are scorched (I did not attempt to view cylinders 1-3, as they are behind a mass of wiring harnesses and vacuum lines), and piston 6 has chunks blown of out it (I could not wholly see the other pistons due to their stroke when the motor was shut off). Curiously, the motor is experiencing little blowby.

Some time ago, the PCM threw P0174 (System Too Lean Bank 2) on two separate occasions while the motor was experiencing detonation. After increasing octane rating, I have yet to the see those codes thrown again.

I fear expensive repairs in the near future if the problem persists. Can anybody provide insight?

Thanks in advance!

**CORRECTION**
The fuel rail pressure sensor vacuum line Should conjoin with a vacuum line from atop the EGR at a rubber elbow into the back of the upper intake manifold, not to the EGR itself. Instead, the vacuum hose to the sensor has been deleted and the inlet port, plugged.
 
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#2 ·
Welcome to my the detonation club. Both my 2001s have the issue with the one with 175k miles being terrible. Always was and I will blend high octane with regular in the summer. There is a TSB on the issue which calls for an octane correction in the computer. Never did it and has pinged for 15 years. Body is going so I don't think I will do it on this car
 
#4 ·
Something sounds strange here. 01 was a 1 year only fuel system with a filter that has 3 fuel lines going to it, a pressure regulator in the fuel tank, and no electronic fuel temp / pressure sensor on the rail.

Does your filter have 3 lines going to it?

Any chance the PO put in a different year (newer) engine with the fuel press/temp sensor on the rail in the car? Are you sure the PCM is the correct one for the engine?

Any codes present (codes can be stored without the CEL on)?

What do the long term fuel trims look like at idle, at 50 mph cruise, and with light to moderate acceleration?
 
#5 ·
Something sounds strange here. 01 was a 1 year only fuel system with a filter that has 3 fuel lines going to it, a pressure regulator in the fuel tank, and no electronic fuel temp / pressure sensor on the rail.

Does your filter have 3 lines going to it?

Any chance the PO put in a different year (newer) engine with the fuel press/temp sensor on the rail in the car? Are you sure the PCM is the correct one for the engine?

Any codes present (codes can be stored without the CEL on)?

What do the long term fuel trims look like at idle, at 50 mph cruise, and with light to moderate acceleration?
Really sounds like the wrong engine as you noted. The EGR should be hooked up and working. No EGR will cause issues. The PCM expects the EGR flow which lowers the peak cylinder temperature. The '01 does not have a fuel pressure sensor, or regulator on the fuel rail.

-chart-
 
#12 ·
I had access to a borescope recently, so I removed the spark plugs and inspected the pistons. Pistons in cylinders 4-6 are scorched (I did not attempt to view cylinders 1-3, as they are behind a mass of wiring harnesses and vacuum lines), and piston 6 has chunks blown of out it (I could not wholly see the other pistons due to their stroke when the motor was shut off). Curiously, the motor is experiencing little blowby.
I believe the "chunks" that are blown from the piston are relief cuts in the top for valve clearance. You may want to look at upper intake gaskets. I think mine were really leaking but not causing the pinging.
 

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#14 ·
The Vulcan is a non-interference motor. Clarity is rough, but this demonstrates the "chunks" that I'm referring to. I replaced the upper intake plenum to no avail a couple months ago and then again three days ago when I replaced the entire intake gasket set. I suspected it might be a culprit as well. I appreciate the input, as it does seem to cause the pinging for some owners!
 
#17 ·
Since you live in Georgia you may consider running a 180 degree thermostat to reduce cylinder temp which may help. I have run a 192 degrees instead of the 195 to 197 OEM one and it helped a little. In Ohio, that really drops the heat in the winter and my wife was complaining about heat when I used a 192 thermostat. I put in a OEM one and it increased the ping. I am not sure how the lower temp will effect emissions or drivability.

My 2001s have rust issues and the silver one (175k miles) is most likely going to the scrape yard this coming winter so I am not looking at the reflash, but estimated it to cost $150.
 
#21 ·
What about the knock sensor itself ? That's the main feedback for the PCM to control knock. I'd look at replacing that before changing thermostats to lower temps. .
Sensor could be out of range or "weak" not giving proper feedback to PCM. Sensor failure is a number one issue in every system in the car right ? So knock sensor could certainly be bad.
Slight ping can be heard as PCM backs off timing in a lot of vehicles but heavy ping I'd change that knock sensor first.
That is assuming OEM tune is in PCM, aftermarket tune then all bets are off.
 
#25 ·
No wonder I'm a Duratec only guy......
 
#30 ·
I put six remanufactured fuel injectors in over the past couple days (Bank 2 first, and Bank 1—below the UIM—today), and I seem to be observing a noticeable improvement in performance, albeit truthfully, it could be the placebo effect, but I don't think so. I was especially content to calculate fuel economy today and discover that my seventeen-year-old automobile still outputs an impressive nearly 20 mpg in the city. She still experiences slight detonation at high load with a 93% octane rating, albeit I am confident that it's improved from what it was. I replaced my lower intake manifold gaskets some couple weeks ago, and while I had the LIM separated from the motor, I took a metal brush to the intake runners, as large deposits of gunk had built up, likely from blowby and the PCV. I think the cleaning contributed to improved performance and lessened detonation, and I intend to reroute the PCV assembly from the crankcase to a "catch can". She's burning what I believe to be normal amounts of oil for her age, but noting the extent of the buildup, I wish to prevent it in the future. I think I will take her to the dealership to have the PCM "reflashed" and the timing retarded in the near future so that I may finally cease purchasing overpriced fuel.
 
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