Evening all. I've been chasing misfires on my '99 E-350 6.8L and need some feedback to make sure I'm not barking up the wrong tree.

I started having misfire issues last fall, but they were random and not throwing codes. They finally got significant enough and started throwing codes for #1 & #6. I swapped in some spare coils, cleared the codes, and tried again. No change - misfires on 1 & 6. I then changed the fuel filter as I have never changed it before. Some overall improvement, but still 1 & 6 were throwing codes. It then dawned on me that it had been 7 years and more than 50K miles since I last changed the plugs & coils. New Autolite platinums went in today. Now I'm throwing misfire codes on 2 & 4 along with the infamous P0171 code.

My plan for next weekend is to swap coils from my collection of spares on 2 & 4 to see if there's any impact on the misfires. I also read that the PCV hoses on these engines are problematic. I moved mine out of the way while I was working on that side of the engine so I suspect that I now need to replace it since I wasn't throwing the P0171 code previously.

I kind of want to know if I'm on the right track to solving this problem. If changing to spare coils clears up the misfires on 2 & 4, should I plan on replacing all the coils since I ran them so long with worn plugs? Am I right to suspect that the PCV hose is the likely culprit for the P0171 code?

Sorry for such a long post. Between changing plugs on the van all day and to still have problems is pretty frustrating. Thanks for the feedback in advance.

 

Also make sure your injectors on those holes are plugged in. The clips break if you so much as look at them wrong.

 

Make sure you put new COP boots, that may be the cause of the miss fire. Also Motorcraft double platinum is what the 6.8 2v uses.also check the IAC behind the throttle body to see if is not hummed up with carbon for the p0171.

 

As mentioned, check the connections on all the COPs and injectors. Sometimes the wire breaks at the connector under the insulation so you won't see it with the naked eye. Use a meter to test it. I had that happen to mine.

 

New boots went in - I just failed to mention it.

I double checked that the connectors plugged in well before buttoning it up. I don't believe that I've got a bad connector as it idles fairly well - just a very slight shake. It really acts up at part throttle cruise when it feels as though the whole van is vibrating rather than a single dropped cylinder.

 

Fix the PCV leak first if it is indeed leaking. Unmetered air getting around the MAF will throw everything off.

What did the plugs look like when you took them out? Any ones obvious not firing right?

 

Plugs looked pretty good to me.

So I need to focus on identifying and repairing vacuum leaks before worrying about the coils. Unmetered air makes everything lean and outside of the pcm's ability to compensate leading to the P0171 code. I know that the goal is no leaks, but it looks like I've got a significant one somewhere for it to run so poorly.

Any suggestions for locating said leaks? I don't have access to a smoke machine and spraying a bunch of carb spray around in a fairly tight and enclosed space doesn't sound the safest to me.

 

I'm not too familiar with the intake layout on the E series but on my Transit connect the p0171 code was from a rip in the rubber flexible section just after the maf sensor. Maybe try using a smoke bomb? The colored stuff that's used for effects.

 

carb spraying isn't dangerous. Go for it.

 

"Spray and listen" usually doesn't work, the PCM is too fast.

Use your scan tool to monitor either the short term fuel trims or the upstream O2 sensor voltages. You'll see a spike in those readings when the spray gets sucked in. I use brake cleaner, it's seems to be a bit less harsh on rubber hoses than is carb cleaner.

You really need to go in with the scan tool and look at individual cylinder misfire counts once you get the intake leak resolved. If you KNOW which cylinder is misbehaving, it's a lot easier than just shotgunning it and seeing if you got lucky.

It would also help to know if you have an OBDi or OBDII calibration. Check the emissions label on the underside of the hood (if still present). OBDII calibrations are far more effective at self-diagnosis than is the simpler calibration.

 

Brake cleaner (at the time, trochlorethane, but now can be perclorethane, tetra, etc) can be really really bad to breathe after it's been combusted, I think it produces chlorine gas. Was checking for vacuum leaks on an '83 Mustang GT and the owner was standing behind it. He was coughing for hours after that.

Better to use some sort of combustible solvent if you're even going to go that route in the first place.

 

Since I'm under the hood, it's pretty likely that I won't be standing behind any vehicle I'm working on.

An unlit propane torch also works but requires greater precision.

According to the MSADS for Walmart's version, it's a mixture of acetone, toluene, and methanol in roughly 50/25/25 proportions. The MSDS doesn't mention any combustion byproducts. All of things can be pretty nasty and appropriate safety precautions should be followed.

 

The cloud of smog that came out of that Mustang started to blow back at me in the wind. I ran.

The "brake cleaner" I use is CRC: 05089-CRC Material Safety Data Sheet | Cleaners / Degreasers from EIS | CRC - Electrical, Industrial Assembly, Wire & Cable Products

Perchlorethylene.

Your brake cleaner is not the same as everyone else's brake cleaner

 

Dang! I wonder how many different formulations there might be for that class of product!

FWIW, I buy the Walmart stuff because it seems I spend an undue amount of time and money there..

 

Maybe that's why it burns so bad when you accidentally get it in your eyes.

I'm not going to have a chance to mess with it until Friday afternoon sometime. Gotta love working 4 10s...