Trying to chase down a rough idle on SOHC after replacing most related sensors. Idle fine, then PCM sets code and idle goes to ****.

[boominXplorer]

Clean it with mass air flow approved cleaner and put it back in. I'd bet $ it fixes your weird rich codes. They rarely go bad but everyone like to shotgun them in for some reason.

 

[C420sailor]

run the OEM MAF, clean it, check the values at idle on forscan and post here. Should increase smoothly with rpm. Dont replace it unless it is confirmed shot.

My idle always takes time to smooth out after I clean the iac. Last time I did it, it would dip low after a rev for a while. Computer adapted.

There’s a saying in medicine that a patient has a right to have as many diseases as he or she pleases. We always like to find a single smoking gun, but sometimes it isn’t that simple.

This highlights the importance of periodic maintenance. Now that you have the equipment, establish a baseline of parameters with forscan (after it’s fixed). Write it in your vehicle’s notebook (always a good idea to keep track of what you did and when) and plug the laptop in a few times a year to see what has changed. You’ll catch things like vacuum leaks and others before they become problems.

 

[Justin_]

Went ahead and cleaned then swapped back in the original MAF, but didn't see much of a difference. I used a can of MAF cleaner to spray it down with.

I also had the ELM327 came in today. Really cool tool. Didn't know there was that much you could do. Blows my basic code scanner out of the water, and was less than 1/3 the cost too!

I can see the exact ABS issues im having, as well as an error code for the rear wiper blade. Crazy.

Anyway, getting to business.

The data got cut off, I ran it for a 15 minute trip, but something happened. Can always run it again.

On this you can see:

1-20: Softly accelerating, then coasting down a neighborhood road.
20-30: Hitting the throttle while pulling out onto a 50 MPH road.
30-137: Dropping into and riding in cruise control @50 MPH
137-230: manually driving behind another car at about 45 MPH.

Next time I will add speed as well. Down the left we have Throttle, Engine Load, RPMs, Long FT1, Short FT1, O2 bank 1 Front, Long FT2, Short FT2, O2 Bank 2 Front, Idle Air Control, Fuel PWM bank 1

From my inexperienced look, it seems when engine load is above ~25% its running fine, its just when it's below that that there is issues.

Next up we have idling

At about 44 seconds I turned off the heater blower, 165 I turned off the headlights, and 175 I turned off the radio (it wasn't playing at any time, just turned it all the way off)


I also did one other test looking at misfires

Down the left we have Battery Voltage, Camshaft Sensor, Misfire Count, Misfire Cylinder 1, Miss Monitor, Misfire condition, , Misfire Cylinder 2, Misfire Cylinder 3, Misfire Cylinder 4, Misfire Cylinder 5, Misfire Cylinder 6

First off, I can hear the exhaust poofing much more than what is noted here.

To me this looks like there is a misfire issue on Cylinder 3. It has the most misfires, and 5+6 that fire either side of it also have misfires. It could just be knocking the rhythm off a touch and causing erroneous hits on 5+6.

About 9 months ago I had an actual misfire issue on Cylinder 6 that threw codes, and it was diffrent than this. In that case it turned out to be a bad fuel injector.

Just going over other articles I wonder if the exhaust valve is not seating right on cylinder 3. That would cause a poof out the exhaust for sure. Will deffinitly try a leakdown test when the tool gets here and see what happens.

Let me know what yall think. Im making educated guesses here, but this is the first time im working with tools like this.

 

[Justin_]

Thinking more about it, I thought I had a vacuum leak a good few months ago because I was hearing a hissing noise from the rear passenger side of the engine. Could be a leak in 3.

Other interesting thing is right near cylinder 3 is where I ended up with a hole in the valve cover after rolling. Could be unrelated, but who knows.

 

[C420sailor]

Yeah, your O2 sensors are showing max rich at idle, and the PCM is pulling as much fuel as it can.

What is the raw reading of your MAF at idle? Off the top of my head, my SOHC runs like 0.7lb/min or something in that ballpark.

Also...ECT. Engine Coolant Temp. Make sure those numbers make sense. If they're pegged in either direction, that'll cause all sorts of mixture chaos.

 

[Justin_]

Yeah, your O2 sensors are showing max rich at idle, and the PCM is pulling as much fuel as it can.

What is the raw reading of your MAF at idle? Off the top of my head, my SOHC runs like 0.7lb/min or something in that ballpark.

Also...ECT. Engine Coolant Temp. Make sure those numbers make sense. If they're pegged in either direction, that'll cause all sorts of mixture chaos.

When the engine is warmed up the coolant temp reads 185 to 190 Fahrenheit which should be about dead on.

The OEM MAF is jumping around between 3.4 and 4.3 grams a second (~0.45-0.57 lb/m) and seems to average out around 3.8 g/s (0.5lb/m) this is with the idol sitting around 660 and ambient temperature of 31 Fahrenheit

This is fairly consistent albeit slightly higher than the aftermarket MAF I had in here. Or it could just be a temperature difference from when I checked that one.

Tomorrow I can get the ELM327 back out and plot you a graph.

 

[donalds]

I knew you'd like it

Best tool you can buy for a Ford imo

 

[boominXplorer]

Make sure you pull the negative cable after swapping the maf so it can relearn. That won't have nothing to do with a missfire though.

 

[Justin_]

...That won't have nothing to do with a missfire though.

Yeah.

I've been over some posts on other sites and am wondering if the exhaust valve is not sealing properly on 6. That /could/ explain the gentle poof on the exhaust and if it wasn't burning on every stroke it would be sending extra gas, and also oxygen down the exhaust. Under higher pressure of extra load on the system it might be able to smush it in place.

Is that something that would make since??

The leakdown tester showed up today, but I didn't get a chance to grab it from the store. Can hopefully see what that cylinder does tomorrow.

 

[Justin_]

Although that would only be doing it on one side...

 

[boominXplorer]

You already try the basics like change plug and swap wire?

 

[Justin_]

You already try the basics like change plug and swap wire?

Yes, did that back around March. From what I remember everything looked fine then, but can definitely pull the plug out and get photos now. It's been about 9 months so if there was any build up it should be back by now

 

[boominXplorer]

I assume it was the same before the plug swap? Have compression gauge?

 

[Justin_]

I assume it was the same before the plug swap? Have compression gauge?

Yeah, new plugs and wires did nothing.

I dont have one, but I can grab one when I pick up the leakdown tester tomorrow. Ill try to go over everything this weekend.

 

[Justin_]

So, good news. I think we are getting somewhere. Was a bit tight on time so I didn't leak test all of the cylinders but I think I got what I needed.

Cyl, PSI, % loss (low/high), Plug status
1.....150*...80/15.........................Base had LOTS of carbon buildup. electrode also had buildup
2.....140.........................................Base had carbon buildup. electrode was good
3.....153.........................................Base had carbon buildup. electrode was good
4.....150.....50...............................Base had carbon buildup. electrode had some minor buildup
5.....140*...45...............................Base had carbon buildup. electrode had some minor buildup
6.....145*...80/15.........................Base had LOTS of carbon buildup. electrode also had some buildup

All the plug insulator tips were fine. None were cracked.

* Schrader valve in tester was bad. the pressure is AT LEAST this much


Please feel free to correct me where I am mistaken, but to me it looks like cylinders 2-5 are fine. There is some leakage out the oil rings, but they have pressure. Definitely not affecting mix. Cylinders 1+6 however have issues. When I connected the tester the pressure was VERY low. I was looking at up to an 80%+ loss on them, however, given some time they would fluctuate up and down then seal up. If I disconnected the tester and reconnected it, quickly loading the cylinder with ~100 PSI they would seal up faster. In both situations the leak was out the exhaust. Seems like over time carbon built up on the exhaust valves and is preventing them from fully seating.

The guy I got the truck from had the EGR unplugged. Back when I got it I asked him why, or if they just hated emissions stuff. He told me there was a reason, but they didn't remember it. It had been years since it was his main truck, so he didn't remember much about the maintenance. /Maybe/ this is why.

Im guessing there is poorly burnt or unburnt fuel leaking out of/leaving 1+6 (thus extra O2) that is causing the engine to adjust lean, and then underperform from it. Then when I idle it is running lean enugh to have issues burning, thus making things worse.

I suppose it's also possible that some of the other valvetrain components have problems, but I would think this would be where to start. I know the valve train aeria is rather clean. I pulled off the passenger cover to replace it a while back and found basically no gunk in there at all.

So should I just get some CRC valve cleaner/seafoam and see how that does?

Normally I would want to go all the way and get them super clean, but i'm planning on replacing the engine within about 5 months anyway, so as long as it lasts that long im not to worried (as far as something potentially major anyway).

What do yall think?

 

[Justin_]

So I have never looked into valve cleaners before. I have always heard stuff like seafoam be lumped in with fuel additives, oil additives, and o-ring rejuvenators as "You shouldn't just chuck stuff into your car, you should fix the source of the problem" and people just generally ****ting on mechanic in a can solutions. However, now that I am looking into it I am seeing a lot of articles and guides, including from places like Napa, about how you should use seafoam as often as every time you change your oil and that you really can't use too much.

I would guess that, as far as seafoam goes, its somewhere in between the two stories. Could somebody here with some more experience tell me what they think the proper use and cautions on a product like that is? I am searching around for an answer, but I hear loud voices on each side (admittedly leaning towards 'its totally safe and will, if nothing else, not make anything worse') and I really am just getting more confused here.

 

[C420sailor]

You can absolutely try it. It won’t hurt.

My only thought is this…exhaust valves usually aren’t carboned up. They get hot as ****, and typically stay clean. A leaky exhaust valve is usually because of a mechanical issue.

But fuel system cleaners can’t hurt to try.

 

[Justin_]

Well It didn't do much, C420sailor was correct there.

Still about the same.

When on cruise control it sits around 0 LT trim. When on cruise doing 90MPH the ST trim sits at +14.5, but does not fluctuate.

When coasting under no acceleration the ST goes to max negative.

When in park the ST and LT trim go to max.


Occasionally when I was driving I saw the data from the O2's go to 0 with no changes for several seconds, even if I adjusted the throttle. However I cant see this in the graph. I am having a bit of a hard time reading the graph though. Guessing ForScan really is not made for hour long readings.



While I was poking around already anyway I went and pulled the driver side valve cover. Wasn't as bad as I was worrying about, but did require removing the fuel rail witch was kinda annoying. I found that it was a bit more gunked up than the passenger side, but nothing terrible. Ill post a photo in a bit here. Im trying to see if the cylinder 6 exhaust spring is broken or something, but not seeing much yet. Is there anything in particular I could look for.

ForScan file can be found here

 

[Justin_]

Well unless anyone has something else to suggest I think we are about done here.

We discovered that there is an issue inside the engine preventing some of the exhaust valves from ceiling properly and it's probably not something easy to get at.

Like I said previously, I'm already planning on replacing this engine next spring anyway and I've ran it on thousands of miles of road trips like this so it's not like it's doing terrible. Guess we're just going to leave it at that.

Thanks for the assistance though guys!

 

[boominXplorer]

Your timing is probably off from guide wear. Both banks have lower than normal 4.0 sohc compression so it more than likely valve timing.