Higher RPM (4000+) detonation?

[01rangerxl]

Sometime within the last month or so, my truck has developed detonation at over 4000 RPM. Below 4000 RPM it runs great...very smooth, good power delivery, seems perfectly tuned. Above 4000 RPM, it's rattle rattle rattle, and power seems to drop off, whereas it used to be pretty good right up to the 5000 RPM HP peak. Used to be able to run the truck up to 5500+ RPM (as high as the trans would let me go before shifting), but if I try it now, I get the flashing CEL for cat con destruction warning. Truck will not set a code for anything, probably because it's running fine the majority of the time where it is below 4000 RPM. I don't want to hammer it to death just to try to force a code out of it though.

20K miles ago, I did plugs (went from Motorcraft to Denso Platinum TT), wires (original for Prestolite, which should have been the OE supplier), cleaned the TB, and threw in a Motorcraft reman MAF. The original MAF is still good but needs cleaning. As a first step I will probably clean the original MAF really well, then put it back in and see if there is any change. If no change, then move on to the plugs and wires. Denso Platinum plugs should not be shot at 20K miles, but I have run a LOT of E85 through this truck, and E85 is hard on plugs. I'll check gap and condition, and maybe just go ahead and replace them again.

I kind of doubt there is a ton of carbon on the heads because this truck has not really been babied or grandma driven, but it does burn oil and has for over 100K miles, so maybe there is. I have never SeaFoamed it or anything, maybe I should?

I also wonder about the cats on this truck. It has never thrown a code for the cats specifically, but it has burned oil since around 40K miles, so would it be safe to assume there is buildup? I did run a bottle of Prestolite/Mr. Gasket "Cataclean" through it, and that did seem to improve responsiveness, but did nothing for the pinging, and could just be a placebo effect.

The coil is original...should it be a suspect?

Just curious to hear what others may have found in situations where an engine only detonates at higher RPM.

 

[artificialist]

Fuel filter? A fuel filter clogging up may not give you enough fuel for full throttle operation.

I suggest replacing that filter, and then hooking up a fuel pressure gauge to see if fuel pressure is within spec even at full throttle.

Also, sometimes knock sensors can fail, but not set an error code. I dealt with this once on a 1993 Buick Roadmaster.

 

[01rangerxl]

Sorry, forgot to mention I replaced the fuel filter this year with a Wix. I have not tested the fuel pressure yet. It has none of the typical signs of a dying pump. I think the fuel system including injectors should be clean due to all the ethanol, but I don't know for sure.

No knock sensors on this engine, everything is done off the MAF/O2 sensors. O2 sensors were replaced with direct fit Bosch at 100K when it threw a code for one of them (I replaced them all).

 

[Rand]

was the timing chain ever fixed?
that was the year they had bad tensioners

 

[oldhp]

Is this a flex-fuel truck? If not flex-fuel and using E85 I would think it would run stupid lean which would cause detonation, and would eat plugs because of high cylinder temps.

 

[Virtuoso]

Burning how much oil?

We drove a Saturn that ate a quart every 700 to 300 miles (depending on age) and the cat lived. We drove that car for about 90,000 miles. YMMV of course.

Personally, I would swap the MAF first, without cleaning it, just to see what happens.

 

[01rangerxl]

Originally Posted By: Rand
was the timing chain ever fixed?
that was the year they had bad tensioners



This is the 3.0 Vulcan, it should be good.

It is a Flex Fuel engine as well, from the factory.

 

[01rangerxl]

Originally Posted By: Virtuoso
Burning how much oil?

We drove a Saturn that ate a quart every 700 to 300 miles (depending on age) and the cat lived. We drove that car for about 90,000 miles. YMMV of course.

Personally, I would swap the MAF first, without cleaning it, just to see what happens.


The amount it burns varies a lot depending on use, but I would say on average, a quart in 4K miles, for most of the last 100K miles.

Going to try the MAF first. I might have time to play with it after work tomorrow.

 

[Colt45ws]

Could be MAF; Might be a weak fuel pump too.

 

[bvance554]

What fuel are you using? I think I'd try a little higher octane and see what happens before I started throwing money at blindly replacing parts. If it has only been in the past month could it be the change in the 'winter blend' fuel is causing it?

 

[andyd]

There is no need to the wind the poor thing that high. Detonation is not good for piston crowns and exhaust valves. It is caused by a lean condition. A weak spark usually causes a rich condition.

 

[Trav]

Quote:
20K miles ago, I did plugs (went from Motorcraft to Denso Platinum TT

Check the plugs first, i see some of these TT plugs erode the gap in a short time.
Try Autolite double platinums.

 

[NHGUY]

4000 rpm? This a pushrod engine,not an Indy car.Found its home for many years in Taurus cars (non SHO).Find a 4.0 OHC engine Ranger,or drop to an OHC 2.3 Pinto powered oldie.Then rev-er-up.

 

[Trav]

4000 RPM is nothing. Most unmodified push rod gasoline engines redline at 5500+ with the right valve springs, cam, etc 7K is easily doable.

 

[The_Eric]

Originally Posted By: NHGUY
4000 rpm? This a pushrod engine,not an Indy car.Found its home for many years in Taurus cars (non SHO).Find a 4.0 OHC engine Ranger,or drop to an OHC 2.3 Pinto powered oldie.Then rev-er-up.

Indy car or no, it shouldn't detonate.


Originally Posted By: Trav
Quote:
20K miles ago, I did plugs (went from Motorcraft to Denso Platinum TT

Check the plugs first, i see some of these TT plugs erode the gap in a short time.
Try Autolite double platinums.


Wouldn't surprise me. I think that the TT is Denso's low cost platinum plug.

 

[Trav]

The TT was originally only sold by AA. It was/is the cheapest platinum plug they offer usually on sale for $1.99
When its a high speed misfire ignition is usually the culprit and eroded gaps are more often than not the cause.

http://www.densocorp-na.com/vision/2009spring-summer/aftermarketadvances_sparkingdemand.php

 

[OVERKILL]

Sounds like it may be the MAF to me. I'd swap in the old one and go from there. Which as you said, is your game plan.

 

[Trav]

Is that high rpm miss with no MAF code a symptom with Fords? I don't know but most GM MAF sensor problems are usually accompanied by hard starting, stalling and sometimes even smoking after start up.

Your right though there could be a leak after the sensor or something with the sensor itself. I figured the MAF would have thrown a code but now i think about it my Expedition didn't and it had a broken (rotten) band clamp on the round filter housing.
Scan tool data would be helpful.

 

[01rangerxl]

Thanks for the heads up on the Platinum TTs...yes, they were $2 a plug. I will pull one or two when I look at the MAF and see how they look.

Yes, I know a good scan tool could probably pin point it. We have one at work, I think a Snap-On, but generally it's just the actual mechanic who uses it, so I don't know what all features it has. Might hook it up to the scanner at work on Monday since mine doesn't do much other than spit out a code if there is one.

 

[01rangerxl]

Originally Posted By: NHGUY
4000 rpm? This a pushrod engine,not an Indy car.Found its home for many years in Taurus cars (non SHO).Find a 4.0 OHC engine Ranger,or drop to an OHC 2.3 Pinto powered oldie.Then rev-er-up.


Well this unlucky Vulcan found its home in a pickup that gets flogged, and with 150HP to move nearly 4K lbs, it's just going to have to work a little harder than one in a Taurus.

If I just took it over 4K RPM for the first time and it did this, I probably wouldn't think much other than "oh, I shouldn't do that," but this engine used to run great at any RPM right up to 5500 which is as high as the trans apparently cares to go. Because it wasn't an issue before, and detonation is bad, I want to figure out what's going on.