I have a misfire mystery going on in my girlfriends 00 ranger maybe you guys can help me with.

What is going on, is there is an intermittent misfire on #4. I have an ultra gauge hooked to it, so most of the time when it does it, it will flash a pending code. A lot of the time, the pending code will go away, but sometimes it will set the PO304 code.

First I tried a tune up. New plugs and wires, air cleaner, cleaned out the throttle body. This cured it, for a short while. Then we were back to the pending code / setting code for #4.

When I pull the plug on #4 it is sometimes wet with gas. If you put a new plug in it runs fine for a while. In fact the last time we took a several 100 mile trip with it right after plug change, and it ran great. The pulled plugs re always in good condition with no burn, oil, chips or glazing. I have been using the standard autolites that are in advace auto's computer for that engine. No issues with the other 5 so I figure they re good enough.

The day after we came back I get the call... Honey its doing it again. Often to the point of having no power at all.

But it will clear itself usually, if not a new plug for #4 will cure it immediately.

So I thought something is killing this plug.... Or flooding it. SO I ran 2 cans of sea foam though it, put in a new plug and an new wire. It fixed it for a week then it did it again.

Ok I think... maybe the coil pack is bad either killing the plug or just not firing it at all? So since the pack has never been change in its nearly 300K life (to my knowledge, shes had the truck since about 60K) What the heck.... a new coil pack for the old thing.

I am waiting patiently for the call to come..... "honey its doing it again".

I have not had the chance to clean the MAF but we are talking misfire on one cylinder, every now and then with no real conditions that set it off. More often than not its a pending code that you can even hear or feel and other times its a full blown miss that drags the truck down. Well for a short while until it clears up or I replace the plug.

3 cans of seafoam surely would have cleared a sticky injector. I realize it could be a bad wire to that injector but I have not had the time to tear the fiddle bits off to get to it to clean and test it... or just replace it.

Honestly Ive had a lot of cars and trucks, I dont remember ever having to replace an injector. Ive had bad wires to them but they misbehave ALL the time. This problem is so intermittent its freaky.

Lets say she calls today and says its doing it again.


Any suggestions on where to hit it first?
She says it does it mostly when its cold or not totally warmed up. Almost always, by the time the engine is hot it goes away.

And hot for this truck is over 185F, which I think its too cold to be running and the thermostat needs changed BUT she thinks cool=good. I keep telling her no, cool is often not good, the engine needs to be up to the operating temp.... which to me means 190-200. Her ranger runs between 170-180 all the time. I doubt thats causing the problem but still.... I think new thermo is in order.

My thinking is since it runs so cool all the time, the issue might be related to a spike in the temp over 180 ish, that gods forbid is opening a crack somewhere to suck air or lose compression.

And a compression test is my next step on #4 if/when it does it again.

Now I have had cracked valves before, I dont recall them acting this way.
After all sometimes the thing will go 100s of miles under different drivng conditions and run fine. I don't think a cracked valve would be that nice.

Shes getting @18 MPG mixed driving, when it runs t runs like a bear. It always fires right up. There is no smoke, white or black. There is no water in the oil, no oil in the water. No audible exhaust leaks. No ticks knocks or oddball noises. For its age and miles almost 300K it runs perfectly.

Well until it has its intermittent issue with the misfire, that isnt bad enough to actually set the code.

Any input you guys can give me is appreciated.

 

Welcome to FTE.
Kinda sounds like the #4 fuel injector pintle is intermittently sticking & causing runny nose mischief, or maybe it has an intermittent electrical problem with its electrical connector contacts, or wiring to it. When it acts out, have a listen to the #4 fuel injector with your stethoscope, to determine if it sounds different than the others. EDIT: Also do the listen test around the head to determine if a valve on #4 is ticking/sticking, ect, in time with the miss.
CCDI=Combustion Chamber Deposit Interference, is known to cause intermittent miss & with the miles on this puppy, flaking off intake valve, or combustion chamber deposits may be intermittently holding a valve open until it clears. The 20oz Techron treatment in a tank at the pump before filling with a PEA containing fuel, along with Fords daily 3 mile 3600 rpm blow it out run during the treated tank, will be good for this condition.
If you think it may be electrical, maybe try a injector wiring/connector wiggle/thump test & see if you can induce, or clear up the problem.
If internal fuel injector deposits are on your suspect list, you might consider trying a 20oz dose of Techron Concentrate Plus in the tank, at the pump before filling, so to get good mixing & if we'll use Chevron, Texaco, Caltex, or now Shell fuel, all of which have some PEA in their ad pack, that along with the added Techron, will raise the treat rate 10X above pump gas alone & will usually bring results in one treated tank.
If things get better suspect internal injector deposits. Some thoughts for consideration, keep us posted on your trouble shoot.

 

I recently read a book on OBDII. It said that the misfire code can be generated by many sources. The crankshaft sensor is the source. The combustion stroke is seen by the computer to have been less than expected using the crankshaft sensor. Further anything that has to do with a problem with the combustion efficiency can cause a misfire.
Additionally you are noticing the misfire, before a code has been set. So it's noticeable and goes away after the engine is totally heated up.
So the next question to ask is how's the cooling system? What changes due to the system being totally heated up?
Start there and see what's up.

 

Any coolant loss?

If it's a gasket (intake or head) that is failing, a compression test alone might not be enough to pinpoint the problem....you really need to do a cylinder "leak-down" test, as well.

FWIW, here's my experience with a #4 misfire on the 4.0L OHV: https://www.ford-trucks.com/forums/2...ke-gasket.html

 

I got the call...
She said it was missing really bad, then about 10 min later she said its running fine now.

Pretty much the MO of this thing.

I've always had good luck with seafoam but I will definitely give the Techron Concentrate Plus a shot. I would stick the stethoscope on it but it only does it when she has the thing out running. It never seems to do it for me.

However I didn't think of poking around with the wires and trying to make do it. That would be an easy test.

I never used Techron Concentrate Plus before, but hey.... I'm willing to try anything.

Thanks for the input!

 

There was a mystery leak on the front of the engine, a local mechanic and I went over it for an hour the source was not found, it was leaking a qt a day. It had litte puddle on top of the engine behind the alternator thats all. We both concluded it was that lower intake gasket leaking.

I know ya aint suppose to use the stuff but we dumped a big bottle of bars leak head sealer in it, a week later no luck. So we drained and flushed it, then tried Blue devil head sealer, it sealed it right up and it hasn't lost a drop in a couple months.

Now to my knowledge that water port is not adjacent to #4 piston correct?

If it is, perhaps a tiny bit of leak is getting into the cyl and causing the misfire?

No smoke out the pipe at all. No oddball odors.

The BD stuff is still holding just fine so knock wood. I figured with the high miles it was worth a gamble to get a couple 1000 more out of it before it got torn down and resealed, or even rebuilt. My bro and I can do that itll just take more time than the can spare the truck. The plan is, keep it running and keep shoping for a truck deal, if it dies just go buy another truck and park this one in the garage and reseal / rebuild the engine.

I had not considered the leak would be involved with the miss due to the location of the port and the cyl. Unless the head gasket is leaking elsewhere.

I like the flaky injector theory better. LOL

 

The coolant ports are in the front of the engine, close to where the #1 and #4 cylinders are.

A 4.0L OHV that was losing a quart of coolant/day at some point has to have a fairly serious gasket failure (or cracked head). IMO, whatever caused that kind of coolant loss is probably the same thing that is causing the misfire.

I can't say I blame you for using the stop-leak stuff, I understand your reasoning about the high mileage etc. But I'm thinking that, maybe the stuff helped to substantially "seal" the external leak, but not enough of a seal to prevent continued migration of some coolant into the #4 cylinder.

 

Could be.
She says it only does it when its "not warmed up" and she said even when it is, if you shut it off then start it again it runs rough until it has ran a little while again.

I marked the overflow tank, it seem to be about right where I filled it to a while back its not losing any coolant. That does't mean a we bit isnt getting into the cyl.

Wouldnt that cause the plug to burn an odd color?

 

If its leaking coolant into a cyl, the plug in that cyl will likely be steamed cleaned, so should be cleaner looking than the other cyls spark plugs, how much cleaner will depend on how much coolant its processing.
If its ingesting enough coolant, you should have a set, or pending trouble code for a bad upstream O2 sensor/s, as coolant will kill the O2 sensors sensitivity. I found this out after Ford/Dealer replaced my brand new Rangers head gaskets chasing a warranty coolant sipping problem & let some coolant into the exhaust manifold & it took out one of the upstream sensors in just 3 miles of interstate driving on my way home & lit the CEL. Thus Ford also got to replace that new O2 sensor on that job. SO, if you have a lit CEL, or a CEL that comes & goes, or a set, or pending code for a wimpy switching O2 sensor, that might be another clue that you have a internal coolant consumption problem. More coolant consumption thoughts for consideration.
Keep us posted on your findings.

 

That is some awesome info there... I had not considered that the coolant would throw an O2 sensor code. Thanks. I will keep that in mind of it ever does throw an O2 code.

BTW... its never thrown an O2 code in my memory. It hasnt since these issues popped up, not even a pending O2 code. I will consider that a good thing considering it has that now plugged leak.

I'm wondering since it seem to do it when the truck is started, hot or cold and stops once it has run a short while if that idle air valve is not gone wonky. I have cleaned it out several times over the last few months. Maybe I killed it with carb cleaner.

A new one would answer that problem... lol

 

If i missed it my apologies, but have you checked fuel pressure & most importantly does it hold steady with the engine off?

If it holds pressure, i think Rockledge has the right idea about the coolant leak. Does the coolant rise and fall in the overflow bottle as it warms up & cools down?

 

If in cleaning the IAC it wasn't held with the electrical connector end Up, or such that carb cleaner ran into the insulation of the IAC solenoid wire windings, it could dissolve the wiring insulation & cause mischief, or have damaged other solvent sensitive parts.
You can test the IAC by disconnecting its electrical connector when the engine is at idle. The engine should idle worse, or maybe stall, if the IAC is working ok. If no change in idle, the IAC is suspect. Its a common problem part in idle woes & might not respond to cleaning, or cleaning might not last & is probably why Ford specifies replacement when they act out. Cleaning didn't last for me, but was a good step in trouble shooting & isolating my IAC woes.

 

I cleaned the MAF sensor and the other sensor wire in the breather tube the other day it hasn't choked since.

 

Ok that's good feedback. Now lets think about this some more, seeing as how the MAF sensor is to see Only filtered air, you need to find out Why/How it got dirty. Like inspect the air filter for damage & proper fit, make sure the filter air box & air tube are sound & buttoned up properly. If your using a oiled foam or cotton gauze type air filter, consider opting for the OEM paper filter, they aren't restrictive for normal driving & will keep the MAF sensor clean. Make sure the PCV system is working right & you don't have excessive blow by over pressuring the crank case & backing up to dirty up the MAF sensor. More thoughts for pondering.

 

All your links in that thread are 404... got good links?