420A Random Misfire on all 4 cylinders

[estuardowrld]

Welp. This is my final hail Mary since i got the car it’s been having misfiring issues every-time i take the car on the freeway. I’ve changed every part i can think of.
Cam sensor
Crank sensor
Fuel filter
Spark plugs gapped at .50
Wires x2
Ignition coil x2
98 Auto ecu
Egr delete

Only thing i haven’t touched is fuel pump and injectors. Everytime i go on the free way in 4th or 5th gear the check engine light flashes and the dreaded codes come out. I don’t know if it’s a possibility but the old owner had wired in the ecu. Please help

 

[danl]

What did the old owner “had wire”? Had wired what. What are the “dreaded codes”. What do they say?

How is the ignition power transistor? Is the connector in good shape? Is the power transistor looking good visually?

 

[estuardowrld]

What did the old owner “had wire”? Had wired what. What are the “dreaded codes”. What do they say?

How is the ignition power transistor? Is the connector in good shape? Is the power transistor looking good visually?

He wired the whole ecu from what i recall when i first purchased the car. But to be completely honest when i first got the car all the vacuum lines were torn up all car was running on no oil. The codes are as follows p300 P301 P302 P303 P304 P300. I haven’t tested the transistor.

 

[danl]

Ok, those are random misfire codes. So would you say the problem only happens on the highway when the engine is under load? Is it cruising rpm? How repeatable is it? Does the car lose power?

 

[estuardowrld]

Ok, those are random misfire codes. So would you say the problem only happens on the highway when the engine is under load? Is it cruising rpm? How repeatable is it? Does the car lose power?

Yeah it only happens when the car is under load everytime i take it on the freeway it’s a guarantee it’s done this 6 times already. And yeah the car loses power it feels sluggish and the shifts are rough.

 

[danl]

About how much throttle are you giving it when this happens? 10%, 25%, 50%? What are the engine rpm when it happens?

 

[estuardowrld]

25% and 50% Around 4-5K Rpms

 

[TerminalTalon]

You need to test the fuel pressure before anything.

 

[estuardowrld]

You need to test the fuel pressure before anything.

How would i do that?

 

[BLACK'98DSM]

With a fuel pressure gauge. There is a threaded AN fitting on the end of the fuel rail, remove the plastic cap and attach the gauge. You may only be losing pressure under load though, in which case you couldn't see it.

If the ECU wiring has been cut into I would probably start by making sure everything has continuity and good connection. If it were a wiring issue I'd assume the issue as constant but maybe there's a specific vibration frequency exposing the poor connection. You may just consider soldering the connections and adding shrink wrap. I can only imagine a bunch of exposed crimp connectors, based on things I've seen of your previous owner.

Also, why would you be running an auto ECU if the car is a manual? It should run with but there are some map differences.

 

[evil_eagletalon]

Does the car have a catalytic converter?

Has compression and leak down been done?

 

[BLACK'98DSM]

Low compression would indeed cause misfire codes but again, that would be a consistent issue. The dipstick will start blowing out before the misfires though.

 

[evil_eagletalon]

Anytime one is dealing with a misfire a compression test is in order.

 

[estuardowrld]

Hello guys to answer the questions. I mentioned the Auto ecu because it still did it with the auto ecu. I’m running the manual one and it still does it. i did a compression test all cylinders 160-170. And yes i still have a catalytic converter. Also if it is the fuel pressure how would i fix that? I will show you guys my ECU connections.

 

[estuardowrld]

This is how my ECU currently sits i also removed my intake manifold and it’s really dirty gonna give that a clean. I also took out my injectors i’m gonna get them flowed tested and rebuilt.

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[estuardowrld]

Also i don’t know if this is normal but i found some oil coming out of my pcv valve and there’s oil on the intake manifold gasket and manifold itself

 

[evil_eagletalon]

If the catalytic converter is starting to melt or plug up that can cause misfires because the exhaust is not flowing enough causing rich mixture in combustion chamber. Unbolt the cat and look at the honey comb. Maybe post a picture.

 

[estuardowrld]

If the catalytic converter is starting to melt or plug up that can cause misfires because the exhaust is not flowing enough causing rich mixture in combustion chamber. Unbolt the cat and look at the honey comb. Maybe post a picture.

Will do that right now thank you.

 

[BLACK'98DSM]

That's all original wiring for the ECU. No problem there unless the wires are damaged. The plastic sheathing becomes very brittle and breaks off, he tried to cover the harness with tape.

Oil in the intake manifold could mean 2 things. Excessive crankcase pressure or a bad PCV valve. But the PCV valves rarely need replacement.

 

[estuardowrld]

That's all original wiring for the ECU. No problem there unless the wires are damaged. The plastic sheathing becomes very brittle and breaks off, he tried to cover the harness with tape.

Oil in the intake manifold could mean 2 things. Excessive crankcase pressure or a bad PCV valve. But the PCV valves rarely need replacement.

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[estuardowrld]

That's all original wiring for the ECU. No problem there unless the wires are damaged. The plastic sheathing becomes very brittle and breaks off, he tried to cover the harness with tape.

Oil in the intake manifold could mean 2 things. Excessive crankcase pressure or a bad PCV valve. But the PCV valves rarely need replacement.

If it was the crankcase pressure could that cause misfiring?

 

[BLACK'98DSM]

If it was the crankcase pressure could that cause misfiring?

Well yes, but I don't think so in your case. It is typically caused from blowby which can be indicated by low compression. Your compression readings show wear but not low enough to prevent proper functionality or cause misfires.

 

[estuardowrld]

Well yes, but I don't think so in your case. It is typically caused from blowby which can be indicated by low compression. Your compression readings show wear but not low enough to prevent proper functionality or cause misfires.

I am really stumped at this point i don’t know what else it could be. I’m gonna check the fuel pump and the cat as well. I don’t know if this could also be but maybe the crank sensor? When i bought the car the cat didn’t start until i added a new crank sensor. Could it have gone bad again?

 

[jesse12345]

I dont think o2 sensor was mentioned unless I missed it. Were you able to scan the car you can cycle the key 3 times and it'll flash codes at you.

 

[estuardowrld]

I dont think o2 sensor was mentioned unless I missed it. Were you able to scan the car you can cycle the key 3 times and it'll flash codes at you.

Oh sorry but yes i replaced bank 1 and bank 2 sensors.