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Check Engine Light flashes when going down a steep hill
Hi all, I haven't been around for a while, but my old F150 is still running.
It's a 1998, 4.2L, 2wd, automatic... Just over 200K now..
The other day, while coming down a very steep hill, the CEL started flashing. But I wasn't on the gas, so there was no pinging..
When the hill got less steep, the light stopped flashing. (but it stayed on)
The first time it happened, I had the OD turned off. But now it's happened three times on that same hill, and I left the OD on to see if that had anything to do with it. No difference... The light flashes on the steep parts every time.
The code reader shows two codes; P0302, and P0302 pending.
P0302 is misfire on cylinder 2...
I cleared the codes twice, and the light comes back on within a day.
I did a compression test today, here's the results;
#1 ...172
#2 ...139
#3 ...162
#4 ...176
#5 ...172
#6 ...185
So I put some oil in cylinder #2, and the reading came up to 150 for that one..
I'm afraid it might be the head gasket, but it's really strange how going down a steep hill makes the CEL flash when I'm not even touching the skinny pedal. Anyone ever heard of that before?
never heard of that, but the compression on #2 cylinder is somewhat lower than the others........ that being said, the atmospheric pressure at sea level is 14 psi... with a 9 to 1 compression, you should get about 130 psi... Your 175 psi numbers seem high. Possibly the gauge is miss calibrated.
Since #2 is in miss fire you have two NORMAL options for problems... Injector problem, or coil problem...... with the low compression, I would wonder about an injector leaking and washing down the cylinder wall and scratching occurring which would cause low compression.......... If nothing else, I would suggest pulling the plug and injector for inspection / replacement.
-------- this assumes you don't have a head gasket leaking..... any sign of antifreeze loss ? Look at the plug for fouling / water blasting / etc. .............. but you normally would not get the 302 code unless the head gasket leak was VERY NOTICABLE.
never heard of that, but the compression on #2 cylinder is somewhat lower than the others........ that being said, the atmospheric pressure at sea level is 14 psi... with a 9 to 1 compression, you should get about 130 psi... Your 175 psi numbers seem high. Possibly the gauge is miss calibrated.
Since #2 is in miss fire you have two NORMAL options for problems... Injector problem, or coil problem...... with the low compression, I would wonder about an injector leaking and washing down the cylinder wall and scratching occurring which would cause low compression.......... If nothing else, I would suggest pulling the plug and injector for inspection / replacement.
-------- this assumes you don't have a head gasket leaking..... any sign of antifreeze loss ? Look at the plug for fouling / water blasting / etc. .............. but you normally would not get the 302 code unless the head gasket leak was VERY NOTICABLE.
Thanks Steve, I was kind of amazed by those numbers too... 170-185 was much higher than I expected to see on any of them.
...but I figure, even if the gage is off a little, they were all tested with the same gage -so the percentage difference is still there either way. On a couple of them, I took the reading twice and got the exact same number each time.
On the #2 cylinder, I only did the "dry" check once (and got 139). After adding oil I got exactly 150, three times. I even let it sit for 15-20 minutes before doing the third reading, and still got 150.
About 5 or 6 years ago, I replaced the coil pack/plugs/wires. Back then, she was running real bad. The light was flashing and the engine was pinging hard! Loss of power and everything... This one is nothing like that... The engine does have a slight miss/vibration these days, but only at low rpm. When I hit the gas, she still goes pretty good.
One other detail that I didn't mention in the first post... I've had foam under the oil filler cap for a long time now. The oil on the dipstick looks normal, but the underside of the filler cap doesn't look so good. Some people say it might just be condensation, but I dunno about that...
maybe its me? but cylinders 1 , 5 and 6 look a bit too clean. Unless they had been changed recently? Gotta wonder if that is where the minor head gasket leaks are at and might be as Steve(ill) called "water blasting" those and may also account for the elevated compression readings especially on #6.
AS for why cylinder 2 is down on compression, only can speculate and agree with Steve(ill).
with the low compression, I would wonder about an injector leaking and washing down the cylinder wall and scratching occurring which would cause low compression.
I see things a bit different.
Those plugs as shown have a mile wide gap, way out of normal.
At deceleration down a hill with no throttle the fuel injectors are mostly shut down and IAC closed down because there is no need for them under those conditions..
Its built into the program to save fuel and offers a small engine brake effects.
Its also the time when the computer updates its tables when there is much less to do.
If new plugs don't clear the CEL, use a Scanner that has a Trap feature. This is set to freeze frame the code when the CEL comes on, then you know what it is since it may not be cylinder 2.
Cylinder 2 causing a CEL under Dcell seems unlikely under the conditions but stranger things have happened. I say this for the following reason. Misfire codes are based on a cylinder's lack of expected rotation time as measured by the crank sensor. Down hill the truck is pushing the motor through the drive train and fuel is shut down. Maybe it's over analysis but these things are all part of the dynamic overall operation.
Be sure when doing compression test that the throttle is held open a good amount so the cylinders can get enough air to compress and show an accurate reading.
Good luck.
I see things a bit different. Those plugs as shown have a mile wide gap, way out of normal.
At deceleration down a hill with no throttle the fuel injectors are mostly shut down and IAC closed down because there is no need for them under those conditions..
Its built into the program to save fuel and offers a small engine brake effects.
Its also the time when the computer updates its tables when there is much less to do.
If new plugs don't clear the CEL, use a Scanner that has a Trap feature. This is set to freeze frame the code when the CEL comes on, then you know what it is since it may not be cylinder 2.
Cylinder 2 causing a CEL under Dcell seems unlikely under the conditions but stranger things have happened. I say this for the following reason. Misfire codes are based on a cylinder's lack of expected rotation time as measured by the crank sensor. Down hill the truck is pushing the motor through the drive train and fuel is shut down. Maybe it's over analysis but these things are all part of the dynamic overall operation. Be sure when doing compression test that the throttle is held open a good amount so the cylinders can get enough air to compress and show an accurate reading.
Good luck.
Thanks Bluegrass, I thought those gaps looked huge too, but, when I checked them, they were all good. ...if anything, they were on the tight side (.052).
The plugs are "Autolite XP", They were all new when I changed the coil pack and wires at the same time. That was maybe 5 years ago.
For the compression test, I only warmed it up for a minute or so. She wasn't quite up to operating temp, but not stone cold either. I unplugged the ignition system at the alternator, and pulled the fuel pump fuse. Then, with the gas pedal floored, I gave it 8 rotations for each reading. I feel pretty confident that those readings are correct... or at least, they're as accurate as the gage is.
It's very strange how the hill triggers the light to flash. I never heard of that one before. When it first happened, the oil was a quart low, so I thought maybe all the oil was up in the front and the computer thought it was empty (the hill is ridiculously steep)... But that wasn't it either because, after I put oil in, it still happened.
I'm still leaning towards head gasket, but I can't see how the hill would have anything to do with that.
I'll post a pic of the oil cap and dipstick later on. The dipstick oil seems ok, but the oil filler cap has foam on it.
maybe its me? but cylinders 1 , 5 and 6 look a bit too clean. Unless they had been changed recently? Gotta wonder if that is where the minor head gasket leaks are at and might be as Steve(ill) called "water blasting" those and may also account for the elevated compression readings especially on #6.
AS for why cylinder 2 is down on compression, only can speculate and agree with Steve(ill). & maybe add that a valve is getting a good seal.
Thanks man, the plugs were all changed at the same time when I did the wires and coil too. That was about 5 years ago, iirc.
There is a little bit of a tapping sound which could be a valve tap.
never heard of that, but the compression on #2 cylinder is somewhat lower than the others........ that being said,the atmospheric pressure at sea level is 14 psi... with a 9 to 1 compression, you should get about 130 psi... Your 175 psi numbers seem high. Possibly the gauge is miss calibrated.
Since #2 is in miss fire you have two NORMAL options for problems... Injector problem, or coil problem...... with the low compression, I would wonder about an injector leaking and washing down the cylinder wall and scratching occurring which would cause low compression.......... If nothing else, I would suggest pulling the plug and injector for inspection / replacement.
-------- this assumes you don't have a head gasket leaking..... any sign of antifreeze loss ? Look at the plug for fouling / water blasting / etc. .............. but you normally would not get the 302 code unless the head gasket leak was VERY NOTICABLE.
Thanks again Steve, that's an interesting point, about "atmospheric pressure times nine"... I didn't quite understand that at first...
So I just looked up an atmospheric pressure calculator, and I'm at 350 ft altitude, so the pressure here should be 14.52 psi. ...times nine would be 130.68 psi... so I guess that means one of two things...
Either there's so much buildup inside the cylinders that the compression went way up...
Or the gage is off by that much...
If the gage is off by that much, then that means #2 is actually around 98 psi then...?
that is a possibility ( #2 under 100 psi)... I don't know that the compression is 9:1... just giving you a BALL PARK number for compression.. Your right that " it don't matter what the psi is as long as they are similar"... is basically right, assuming they are all over 100.
Intake gasket leak is a known failure on the 4.2 V6.
Some say it is only 97-98s but I have a 2002 that had a bad internal intake gasket leak. It was really obvious though, it blew a steady cloud of white smoke which is actually steam.
If you look at the 4.2 intake gasket you can see that the coolant crossover passage is directly adjacent to the intake tract and separated from leakage only by that O-ring type gasket. The isolator bolts holding the intake on have a weird grommet that can fail, the bolt effectively "loosens" and then gasket leaks. I'm not saying that is for sure what your problem is but it is a known issue. It isn't really that bad to change them. Make sure all surfaces are really clean before putting it back together.
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