Misfire madness

[Frank4]

Finished up head gaskets, ran a little rough threw MAF and 02 codes. Swapped both out and it ran better than it ever had in the almost 15 years of ownership. Fast forward 24 hours, drove it to a friends house 4 miles away and a 100 yards from the driveway I noticed it was running poorly and boom, flashing service light. Got to the driveway and it was barely running. I checked the codes and get (misfire on 4 and 7) p1300, p0304 and p0307. Check for sparks and it’s there. Checked all plug wires( 8mm mcore) for connection at the plugs (plugs new and appropriate) and the coil restart with no improvement. Had a spare CPS laying around, swapped it in and no change. I unplugged the MAF and restarted and noticed it ran better but still terrible. While removing the intake plenum bolts they weren’t exactly hard to break loose. I figured ok maybe a vacuum leak. Swapped in a new coil and torqued and loctited the intake plenum. Started up and I have the exact same symptoms but now showing misfire codes for cylinder #3 and #4.

With misfires moving around I am at a loss. Is a it more possible that I have a short in the wiring loom? Bad gas?
Any help from members that have successfully chased down misfires would be greatly appreciated.

 

[discostew]

When you had your heads off did you do anything with the valves? The exhaust valves stick in the guides. Always on those center 4 cylinders.
Probably not what you wanted to hear.

 

[Frank4]

The heads were decked and had a valve job.

 

[discostew]

What year are we talking?

 

[Frank4]

2000.

 

[Frank4]

Magnecor plug wires are from 2019

 

[boxster]

Read a post that the problem could be the O2’s are not specific to your D2, should be Bosch.

 

[Frank4]

02s are new and live data shows they are at the proper voltage

 

[discostew]

did you put that crank sensor in? Those can act kinda weird. What’s your fuel trim at? You say your 02 sensors are at the correct voltage, those voltages should be fluctuating. Does it store any codes other than those misfire codes?

 

[Frank4]

CPS was swapped with new one, no change. When I said the 02 voltage was good I meant that it was good as in doing what 02 voltage does.

live data says OL FAULT fuel system 1 and 2.

I’ll have to check fuel trim live data again. I am sure it’s all over the place. What kind of long an short numbers should I be looking for?

 

[discostew]

You should look for it to be as close to 0 as it will get. I’m just thinking that if the system is lean ( adding fuel) it could indicate a lean misfire that’s moving around like it is. Then if it’s rich ( taking away fuel) I would be checking the fuel pressure regulator for leaking into its vac hose.
What do you do to it to make it start misfiring and making the light flash? What you described makes me think it’s after driving under ligt load and then slowing down to turn into your friends driveway. Do you feel it misfire? Or is this one of those you never feel because it’s on decel? Called a trailing misfire.

 

[Frank4]

Trailing misfire for sure. I’ll pull some live fuel trim and post. So what do I do if it’s long? What about short? Where does this go?

 

[Frank4]

Wait a minute. There is no fuel pressure regulator on a DII

 

[boxster]

FPR is part of the fuel pump, O2 sensors send voltage signals to ECU which adjusts air/fuel mixture a high signal would be rich or more fuel, low signal would be lean or more air. Higher voltage signal less air, lower voltage signal more fuel.

 

[discostew]

Wait a minute. There is no fuel pressure regulator on a DII

Sorry. I started thinking gems shit.

long term fuel trim is more relevant. When fuel trim gets out of wack it usually goes a little lean in short trim/ then long term makes an adjustment and short term tries to inch back towards zero. If it can’t long term will make another adjustment and hopefully short term moves back towards zero. Now if something minor is going on you will end up with long term getting close to 10% and short term pretty close to zero. But when things get all fucked up and the system can no longer compensate for what’s going on, both short and long term trims will go way past the 10% the system will tolerate before requesting the chk engine light.
So when you have a drivability problem like your describing fuel trim can be a clue.
Can you feel it? Or hear any popping or backfire when it happens? I know trailing misfires you almost don’t feel.

 

[boxster]

You mentioned open loop fuel system 1 &2 could be ECU not switching to closed loop and still dumping fuel.

 

[Frank4]

Sorry. I started thinking gems shit.

long term fuel trim is more relevant. When fuel trim gets out of wack it usually goes a little lean in short trim/ then long term makes an adjustment and short term tries to inch back towards zero. If it can’t long term will make another adjustment and hopefully short term moves back towards zero. Now if something minor is going on you will end up with long term getting close to 10% and short term pretty close to zero. But when things get all fucked up and the system can no longer compensate for what’s going on, both short and long term trims will go way past the 10% the system will tolerate before requesting the chk engine light.
So when you have a drivability problem like your describing fuel trim can be a clue.
Can you feel it? Or hear any popping or backfire when it happens? I know trailing misfires you almost don’t feel.

I haven’t driven it in the street since the breakdown but when it happened I heard no popping or backfires only felt an almost a complete loss of power in Both pedals.

So when the fuel trim is out of control you said it could be a clue, a clue to what?

 

[Frank4]

Also, there has never been a moment since the breakdown that it runs right for even a second. It misses and runs rough and wants to die as soon as it starts

 

[discostew]

So it’s not a trailing misfire. It just started to misfire and now it won’t run right you say you have spark at the wires that are misfiring. So it should be pretty easy to find.
What misfire codes store if you let it run for a while?

 

[rovercanus]

Are you fuel injectors seated correctly?