AJP087

To start off, I might type alot...... and Im new to the forum.. Hi!

This might not be the correct forum etiquette, but my first post is a CEL. I'm sure I'll be doing many searches and reading several hours worth of material for many weeks, ha-ha.




I'll jump right to topic. My Girlfriend bought a 1997 F150 4.6 V8 XLT shortbed, single cab, automatic, about a year and a half ago. Runs great and always reliable. But it came with the engine light on. Previous owner said use premium only. Never asked.

Has a hardpipe intake with cone filter and a flowmaster muffler. I took off the BBK throttle body until the engine light is sorted.

The code I pulled is P0306 . Misfire #6 cylinder. No other codes.

If I clear the code with a scanner the engine light will stay off. Runs real smooth... Always smooth. If I never go above 3500rpms( in town) then no code. But if I go over 3500 rpms, however, like getting up to speed on highway, after 10 minutes or so the engine light with blink several times and stay on.

I do not know if this next paragraph is relevant...
If I use regular gas, it will blink at anything over 3200ish RPMS. If I floor it at higher rpms it sounds like a lifter rattling. Loud, only when WOT. If Im at higher RPMS, and its not floored(passing gear), it sounds normal or light ticking and is smooth.

I started off by throwing parts at it. Here's what I've done in the last few months.

New Fuel Filter
New Crank Sensor (was told it could have metal buildup on end and to clean it, already off, so replaced it.)
New spark plugs
New spark plug wires (Wires not Coil on Plug)
Rebuilt Refurb #6 Injector from Rockauto
New coil pack
New Throttle Body gasket(took BBK off)
Cleaned MAF with MAF cleaner..





.................................................. ................................................

I was reading a 4.6 trouble shooting website and thought someone might be able to interpret this stuff.

Injector OHMS read as followed, with engine warm but not fully warmed up.
1- 16.1 ohms
2- 16.1
3- 16.2
4- 16.0
5- 15.9
6- 16.0
7- 15.8
8- I couldn't get my big hands in there.

Fuel Pressure
AT IDLE
With vacuum on regulator- 30psi
Without vacuum on regulator- 40psi

With vacuum and a good rev from 30 bounces to 40.

Fuel pressure goes down to 0 immediately after turning off engine. Gauge did have leak though, drip of gas. I am unclear if it should maintain pressure after the engine shuts down.


.................................................. .................................................. .



AND
Here is data from code scanner if it helps.

Freeze Frame Data from code scanner- two weeks ago.

P0306
ECT *F 190
STFT B1 .7%
LTFT B1 -2.3%
STFT B2 -8.5%
LTFT B2 0%
ENG RPM 682
MPH 0

SCANNER LIVE DATA

AT IDLE
LTFTRM B1 -6%
LTFTRM B2 -3%

AT 2000RPMS in park
LTFTRM B1 8.5%
LTFTRM B2 0%


O2 sensors seems normal range and functioning.
MAF read .9 ILBS/sec at idle and went up with revs

.................................................. .................................................. .

So that is how far I am with it. I'm unfamiliar with 4.6 engines, and do not know of the common problems that I could look into.

I can go ahead and do a compression check, and change the cam sensor(read it could cause misfire) but Im not sure if either is a problem.





I'm stumped. Any suggestions or advice would be appreciated. I've tried to be thorough. I do not know where to go from here.

Thanks.

Handywoman Teacher

My '98 is in the shop as we speak for the same thing. #6 and #8 misfiring all the time.

plugs, ... nope.

coil, ... nope.

voltage,... nope.

Guess what, .... blown head gasket. Apparently pretty common problem that is going to cost you some bucks, ... good luck.

AJP087

Would that show up in a compression test?

charliedyal

Most definitely. Cylinder will not hold pressure with a blown gasket. Any milkshake in the oil, white smoke, exhaust smell in the coolant?

AJP087

None of that. Coolant is normal, with minimal pressure, no leaks and never needs to be topped off. Oil is clean, changed every 3K with max520, and a k&n oil filter.(oil filter has drainback valve, fixed the morning startup noise) Motor doesn't smoke at all.

I've bought a compression tester, yesterday. I think I will have time this weekend to use it.

charliedyal

Hopefully your compression is good and you trace the issue back to something in the ignition/fuel system, but it sounds like you've tested/replaced almost everything. If the comp on that cylinder is low you either have a blown gasket or valve trouble. Both of which are expensive repairs.

AJP087

So good news is I found the problem.
Bad news, its low compression on cylinder 6.

I tested cylinder 5 and it was at 145 psi. Moved on to cylinder 6 and it was at 90psi. Got discouraged and didn't test any other cylinders.

At least I don't have shop fees.

Thanks for the guidance.

charliedyal

Sorry to hear that. Sounds like its time to do a tear down. You could have a blown head gasket, sticking or damaged valves or seats, or damaged/worn piston rings.

Carcrazygts2

Do a compression test on the entire bank. Likely the truck was overheated and it wont show on cylinder #5 but will show up on cylinder #7. Also do a dry and wet compression test. I wish the best on you choice. If it was I, I would replace the tired 4.6 with a PI Swapped 5.4

AJP087

Im kinda at a crossroads with it.

Still discussing it with my other half as to what we are going to do to it. We're looking at our options as to if we should even keep it and repair it. We've driven it 15K miles since we've had it in its current condition. Everything is in excellent shape. Aside from the heater not working.

If we try and sell it or trade it in for something newer, we don't know what its worth.

If we keep it and repair it, we wouldn't want to spend too much on it.