Misfire resolves in 48 seconds?

[mk378]

If it also runs badly under load while driving(*), it's not EGR.

Suggest doing a standard cylinder drop test to see if it is one cylinder (as a shuck valve, bad spark plug or wire would be) or generalized.

* It's been like pulling teeth to get a clear answer from the OP on that single question.

 

[tomkat22]

Originally Posted by mattd
Physically put you're hand on the tube while it's running at idle and feel it


EGR pipe not super hot near the valve,I can keep my finger on it a couple seconds without getting burned.A little hotter further down the pipe. Are you hinting at a clogged cat?

 

[tomkat22]

Originally Posted by mk378
If it also runs badly under load while driving(*), it's not EGR.

Suggest doing a standard cylinder drop test to see if it is one cylinder (as a shuck valve, bad spark plug or wire would be) or generalized.

* It's been like pulling teeth to get a clear answer from the OP on that single question.


What single question are you talking about? I've responded to every suggestion.

 

[tomkat22]

Strange because compression is decent,149,151,150 and 151. As far as a cylinder drop test I'm not having much luck with that. With two plugs per cylinder I have to remove the #1 plug wire on both coils simultaneously,kinda hard to do before the ECU compensates and raises the RPMs.Plus my hearing aint all that great.LOL.

 

[Trav]

Do you have any codes set when this happens. Did you check the TPS with an VOM.

 

[mattd]

Originally Posted by tomkat22
Originally Posted by mattd
Physically put you're hand on the tube while it's running at idle and feel it


EGR pipe not super hot near the valve,I can keep my finger on it a couple seconds without getting burned.A little hotter further down the pipe. Are you hinting at a clogged cat?


If the pipe is that hot at idle you have uncommanded egr flow. Intake vacuum is pulling exhaust gases past the valve/seat. It should be lightly warm (if at all) until egr flow is commanded then it will be hot. The problem is likely exacerbated by the changes in manifold vacuum from engine load. The spring and/or diaphragm in the valve is junk. Change the egr valve and see if it's fixed.

 

[tomkat22]

Originally Posted by Trav
Do you have any codes set when this happens. Did you check the TPS with an VOM.



No codes set. I monitor the TPS and ECT sensors with my scan tool,a Creader 3001. Suffice to say I am happy with the readings on the scan tool from both those sensors ,they seem to be functioning normally. As for the EGR I suspected it might not be functioning correctly so I fabricated a blanking plate...basically took the EGR out of the equation(temporarily as a test). Made no difference at all with the misfire. The misfire is not trigger by load on the engine,it's trigger by quick revving to high RPMs. That causes the vacuum gauge to start fluctuating wildly at 10-15 hg/in at idle. It slowly returns to normal within 48 seconds if it's allowed to idle. If I can find out what is "moving and changing" during that 48 second wait I think my problem will be solved.

 

[mk378]

If you can reach the fuel injectors you can also do the drop test by unplugging them one at a time.

I'm still not clear on the symptoms. When you drive off from a stoplight for example, does it always run steady and pull strong getting up to speed? I'm not talking about idling or revivng in neutral. Does the truck always go when you put it in gear and gas it, or will it misfire and not go?

 

[Trav]

I am not familiar with dual plug ignition Ford used on that engine but from what I understand one set fires while cranking up to 400 rpm then the other set comes on line?
i would almost suspect an ignition module problem going by what you have do so far, but I really have no idea, its just guessing. If I had it to work on I would have to do a lot of digging on this, the 48 second thing is what I don't get.
Maybe Clinebarger has some ideas.

 

[clinebarger]

Originally Posted by Trav

Maybe Clinebarger has some ideas.


The 48 second thing has me perplexed.......Quick vacuum gauge fluctuations at idle makes me think Worn Valve Guide/s, Weak valve spring, Sticky valve, Or a malfunctioning hydraulic lifter. That's what the basics would lead us to believe & a static cranking compression test is just about worthless if any of the above problems exist.

I would try to isolate WHAT cylinder is misfiring.....
*Disconnect the Exhaust side coil pack control & remove all the plastic retaining clips on the Intake spark plug wires.
*Start the engine & make it misfire
*Pull one plug wire off at a time 'til you find the offending cylinder, It's wise to use a incandescent test light hooked to Ground & place the probe end right next to the coil tower while removing the plug wire, This will keep you from bit by secondary voltage AND prevents damage to the coil as well.

Does your scanner support Mode-6 data? If so.....Select Test ID# $53 & look at the VALUE number on each Component listed, There will be 4 Components listed as this is a 4 cylinder engine.
The VALUE number is the representative of misfires that occurred on that cylinder as a percentage.

*Lets say the VALUE is 7898, Multiply that by .00015.....Equals 1.1847......The cylinder is misfiring 1.2% of the time. The MAX misfire percentage threshold on Fords is usually above 14,000 OR 2.1%. The MAX value must be reached before a misfire DTC will set.
I've seen the MAX as high as 200,000 OR 30%.

.

 

[tomkat22]

I decided to mount the vacuum gauge under dash,it's a handheld under-the-hood type but I was able to adapt it to under dash. It revealed some interesting facts during a long-ish drive. When giving it gas the needle on the gauge drops to below 10 hg and is steady as a rock.When I completely let off the pedal it climbs above 20 and also steady as a rock. However between 10-20 (half-throttle,lite-med load) the needle bounces like crazy.4-5 point swings. I assume that's not normal? I've never used a vacuum gauge before and never owned a vehicle with one. I take it each bounce of the needle represents a misfire?I couple of websites said that is probably worn valve guides. As far as mode 6 data the PCM does not support it on this vehicle. No misfire counts.It did on my 07 KIa Rio,I sure wish it did on this truck. I dumped half a bottle of a popular oil additive before the trip and it seemed to have helped. BTW,the hotter the engine gets(200+)the misfire basically goes away. Conversely the truck is almost un-driveable the first 5 minutes after starting,it runs so rough.

 

[Trav]

If you don't mind wasting a couple of bucks try some GM top engine cleaner down a vacuum line like the brake booster.
I remember when when GM used the dual throttle bodies on the Z28 with the hood inlet. Water would get down in them, this one I did had been sitting a while developed a misfire the above fixed it.

Another way would be to remove the valve cover and use your timing light to view the valves in operation, you will see anything unusual like one sticking right away.

 

[tomkat22]

Originally Posted by mk378
If you can reach the fuel injectors you can also do the drop test by unplugging them one at a time.

I'm still not clear on the symptoms. When you drive off from a stoplight for example, does it always run steady and pull strong getting up to speed? I'm not talking about idling or revivng in neutral. Does the truck always go when you put it in gear and gas it, or will it misfire and not go?



So if the needle is bouncing between 12-17 and I unplug the injector of a "good" cylinder the needle would start bouncing between roughly 8-13? But if I unplug the bad/offending cylinder injector the needle keeps bouncing between 12-17(no change)?

 

[andyd]

Dunno the numbers, Yes, dropping the bad injector, should result in no change in the vacuum readings. Also check the plug when you find the cylinder.

 

[mattd]

The bouncing needle is an indication of a valve train issue. The most likely cause is valve float or valve(s) sticking in guides.

 

[tomkat22]

Yeah that's been my suspicion all along,a compression related misfire caused by something in the valve train. I suppose the 48 second wait for the misfire to stop could be raw fuel being dumped into the cylinder while the misfire is occurring,floods the plug,then needs time to "burn off" and clear before the plug can start firing again.Probably a little oil mixed in there too. Gonna change the valve springs and take a look at whatever else I can see while in there,lifters,etc. Thanks.

 

[brages]

I'm guessing the OP is long gone, but I had basically the same symptoms in my 97 Ranger with 273,000 miles.

I found another guy on the internet saying that this is due to recessed valve seats. The logic is that the hydraulic lifters pump up when you rev the motor, then when the engine returns to idle, the valves do not close completely until the lifters leak back down a bit. After the lifters leak down, the misfire resolves itself.

My problem started getting a bit worse and would die when you slowed down at a traffic light sometimes. Cylinder 3 was showing the misfire.

Took off my head, and sure enough, the cylinder giving the misfire when RPMs come down (#3) was showing recession on the exhaust valve. I took the head to a old-school auto machinist and he found a tiny crack under the magnaflux and advised that I buy a new head. He said that it's not uncommon for these engines to "eat" their valves.

I didn't want to pay the money for a new/rebuilt head (hard to find under $400), so I pulled a 120,000 mile head from the pick-a-part for $50 and brought it to the machine shop. No cracks, good valve seats, the machinist worked it over a bit and I put it on. Fixed the problem!