misfires even cylinders only, i’m stumped

hello, I’m new to the forum because I am new to this truck. I have spent hours going through all the threads looking for a similar situation as mine and I have found several, yet no one seems to actually come back with what the solution was, if and when they find it. So I am stumped on this particular situation. a week ago I was driving, and out of nowhere The truck started running very, very poorly, misfiring, running rough, and the CEL started flashing. I had no voice but to drive the 5 miles home from there. I did basic troubleshooting and got a hold of tech stream and a cable to plug into the truck, and I was originally given the codes of multiple misfires and cylinder six misfiring so I pulled a plug and they were long overdue, so I replaced all eight spark plugs, as well as the ignition coil for cylinder number six. That did not fix the issue, because after that, I now have misfires on cylinders 2,4, and 8 with an occasional misfire on six again. I unplugged the upstream sensor on bank two to try to rule out the Cat and it ran somewhat better, but still had some misfires. I changed the fuel filter, but I’m not sure what to look at next. I’m on a very very limited budget so I don’t have the money to just start replacing things, I would like to actually diagnose what’s wrong and repair what needs to be repaired. I do have tools and I do have a meter and that type of stuff. Can someone please help point me in the right direction. It should say in my profile, but I have a 2000 Access cab SR5 4.7 L four-wheel-drive with 247,000 miles on it. The timing belt looks good. Not sure when it was changed. Please let me know if there’s any other information I can provide, like I said I do have tech stream in order to assist with troubleshooting. since I cleared the original codes, no codes have come back other than the unplugged sensor at that time obviously, which has been plugged back in and that code cleared. please help!!

 

Is it still running like shit?

 

When’s the last time the timing belt was changed?

 

This ^

Seems like the timing belt may have skipped a tooth on that side. Alternately (although not likely IMHO) you may have a fuel delivery problem on that side of the engine only.

 

Would also look into vacuum leaks. Spray carb or brake clean around the intake manifold gasket area while the truck is idling. Engine RPM changes while spraying you found a vacuum leak.

 

Only even cylinders. So only the passenger side.

Remember: Misfires are usually either bad spark, too much air (i.e. leak), or too much/too little fuel.

if I recall, the coil packs are wired weird; like 1-4-6-7 and 2-3-5-8 so it’s probably not working. (I think it’s the coils wired that way, not injectors).

Given it’s only the passenger side. This rules out the MAF reading wrong and feeding ECU bad air volume intake info (which is how it knows how much fuel to dump), that would likely affect both banks if MAF was fucked.

Given it doesn’t impact the driver side, it’s likely not the fuel pump (but still could be, I just highly doubt it), I suspect the fuel pump is probably delivering enough fuel…

Given it’s all cylinders, it’s likely not coil packs, so if you made the mistake of buying aftermarket ones, they suck fucking ass, reinstall your OEM ones now, and blender buy aftermarket again.

Given you’re saying it’s ALL cylinders on the passenger side it’s likely not the intake gasket; that can blow on all cylinders but I can’t remember ever seeing it on any of my many cars over the years. And for 1st gen guys it’s always only one or two.

So what could affect all four cylinders then?

Well, let’s start easy. Dumb question, but did you check the vacuum hose that runs from above the middle two passenger cylinders (from fuel pressure damper) to the intake? That acts as a vapor return line and also pulls vacuum off the intake to stanilize pressure on the passenger rail.

If that hose is OK, the ends aren’t cracked, and running a temporary hose there doesn’t fix it, you may want to consider that fuel damper on the rail is toast. It looks almost like a metal top hat, or espresso pod for an instant espresso machine.

Those are my best bets on your issue. It’s entirely possible your fuel pump is dying and just can’t muster up the power to push fuel hard enough to the passenger rail but I doubt it and would expect you to be throwing ‘running lean’ codes, maybe?

 

so I have some new info, I unplugged both o2 sensors on the problem side to clean them and started the truck before they were plugged back in- and no misfires! when I had just the upstream sensor unplugged I still had misfires, a reduced number but still misfires. does this indicate a bad cat? possibly ruined when I drove home with the bad coil?

 

oh and it’s obviously running rich as can be, trim at +21.75 on that side. I suppose I need to swap the sensors with the other side, unless there’s is a test I can do with my meter without removing unnecessarily?

 

You’ve likely got a bad O2. Upstream is a/f ratio sensor, what helps the ECU set fuel trims by measuring the combustion output. That aligns with prior symptoms.

DO NOT buy aftermarket sensors.

DO NOT buy replacement parts on scAmazon or fleaBay.

ALWAYS replace your O2 sensors on bank pairs (upstream/downstream) at same time.

Look up your replacement part on www.densoautoparts.com and note that the upstream may be listed as “air/fuel ratio sensor”, while downstream is listed as “O2 sensor”. ALWAYS get the “exact fit” part not the “Universal” part, you should NEVER cut an O2 harness for any reason! Also note that sometimes RWD vs. 4WD will have a different part number, read the description carefully.

Once you have your part numbers, I recommend using Summit Racing or RockAuto for best pricing. I feel Summit has the best customer service and often cheaper shipping (free).


CHEAP TROUBLESHOOTING NOTE: If the Denso site shows your upstream sensors are the same part number and you have the V8, you can swap the upstream sensors passenger to driver side, and see if the problem echos to the other side. Sanity check et al.