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Bad misfire troubleshooting ideas

jepherz

Staff member
Joined
Aug 8, 2004
Messages
7,877
Location
KC, Missouri
Well, it's the second trip I have made to Minnesota and have pretty much gotten stranded. The problem is a horrible misfire that seems to start around the 3 hour mark and keeps getting worse until I can hardly keep a steady 50 mph on the highway. This vr4 is completely stock and I recently replaced the fuel filter and checked the pump sock for dirt. I figured I had the problem fixed because the car seems to run fine when cold. What would get worse and worse with heat? The coil pack? Maybe a bad fuel pump?
 

toybreaker

iconoclast
Joined
Apr 30, 2006
Messages
3,581
I'd swap a coilpack on there if you have a spare with you.
 

mitsuturbo

Well-known member
Joined
Jun 2, 2008
Messages
3,544
Location
Near Seattle, Washington
I agree with coilpack. Maybe the PowerTR unit, since they're both a bit distant from the "serious" heat.
 

broxma

Well-known member
Joined
Nov 16, 2009
Messages
911
Location
San Antonio Tx
What is a misfire other than an unexpected or non-existent firing of the ignition? The wife's car just developed a misfire on 1 and 3. Changed plugs, no difference, changed coil packs, gone. Provided the timing is correct and the CAS is fine, gotta be in the ignition. Plugs, wires, coils, ignitor. It'll be one of those 4 things. If it's not, it's more serious, but since it runs normally for a long time then develops it, I'd say it'll be one of those 4.


/brox
 

CarRacer

Well-known member
Joined
Jun 28, 2007
Messages
4,371
Location
Shakopee, MN
I should have a spare coil and igniter in my garage. I'll toss it in my car, it's been slow this week at work so I should be able to bust out to go help you if needed. I work in Edina, so hopefully that's close to where you're at. If we don't have the parts we can still take stuff off of my car to troubleshoot.
 

jepherz

Staff member
Joined
Aug 8, 2004
Messages
7,877
Location
KC, Missouri
Well, Car racer helped me out a ton, let me swap in his coil pack with his garage space and tools; I really appreciate that!

Anyways, the car got worse and worse on my drive home, so I left it in MN and took another car back. I'm now thinking it HAS to be the fuel pump. After reading ANDRES post from this thread, the symptoms are identical.

Now the task is to find a fuel pump. The car is completely stock and I'd rather not cut up the sending unit. Looking at pumps on RockAuto, it seems like a bunch of them are generic pumps and they send out hose clamps and hose and expect you to cut up the sending unit anyways. Does anyone have stock pictures of a VR4 sending unit vs. a DSM unit or 2g DSM unit? Or any experience buying a pump from any of the suppliers that bolted right in with the o-ring an all? I'm looking over this thread and recalling what I'm mentioning there, but I'd like pictures or other proof if there is any.
 

toybreaker

iconoclast
Joined
Apr 30, 2006
Messages
3,581
Do you still have the stock evap system installed on the vehicle?

When you remove the gas cap, do you get a big "whoosh" of air entering/escaping the tank?

Do you hear any funky "boingy" type noises coming from the fuel tank while driving?

You might have a plugged tank vent/restriction in the vent system ...
 

jepherz

Staff member
Joined
Aug 8, 2004
Messages
7,877
Location
KC, Missouri
Yeah, the car is stock down to that stuff. Yea, that's possible. I had to use the POR15 tank sealer years ago when I first got the car running, and every now and then, it does "wooosh" when I take off the cap. However, it seems odd that that would have never caused a problem before and all of a sudden started. Plus, I took note when I pulled the gas cap off at the gas station when I was having problems, and noticed there was no wooshing.. The fact that it is getting worse and worse sounds more like the fuel pump failure description I found from above.
 
Last edited:

iceman69510

Turn Right Racing
Staff member
Joined
Mar 5, 2001
Messages
10,964
Location
Michigan
I have a stock VR4 fuel pump (working when pulled) if you want it.
 

jepherz

Staff member
Joined
Aug 8, 2004
Messages
7,877
Location
KC, Missouri
Well, I went back to get my car this weekend. Swapped in a new fuel pump from orielly's. It was a bolt in and no modification was needed to the fuel sender at all. Also put in a new fuel filter and fuel pump sock. Problem fixed! Thanks for the help, guys.
 

DR1665

Well-known member
Joined
Oct 19, 2005
Messages
4,642
Location
Iowa City, IA
Tis the season for fuel system troubleshooting...

I'm in a similar boat. Replaced fuel filter, orange fuel came out, drained tank, clear fuel came out. Changed CLT, as engine runs fine when cold, but shitty when hot.

I'll check the fusible link suggested by Andres in the other post, but I'm waiting until I get a logger on it before I drop the coin on parts. Could be a janky fuel pump (car has 176k+), could be a gunked up O2, could be a worn out alternator pushing crap voltage when hot, impacting pump voltage.

Strange things happen when you get down to that lower current limit. I figure I could just start swapping bits from the other Galant, but even without having to buy new parts, I'd rather not waste the time.
 
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