Yet another redtop SR misfire thread

[Monica Blowinski]

Yes, yes I've used the search function many of times.

So background: The car came pre-swapped. It drove fine, but had some typical issues (leaky blowoff valve, replaced a MAF, yadda yadda). The car developed this come-and-go misfire, which has lead me down a bumpy road. After getting tired of dealing with poorly done wiring, I opted to order up a wiring specialties harness to solve all those issues at once. The car always had a slight hiccup on startup, but drove well, so I left it alone. 2000 miles or so later, the misfire is back. On cold start, the engine will stumble and miss for a second or two, but I can normally throttle it away. The car will jump up and hold a good constant idle, then slowly drop it's way back down to a 900rpm or so steady idle once warm. If I keep the car moving at operating temp, it's okay. It feels a little under powered, but not terrible. Once I get caught in traffic, or stop for gas, or let it idle for a period of time, it sputters like crazy. The car likes to break up anywhere from 2,000 to 5,000 rpm. Sometimes it'll drive itself out, sometimes it won't.

The misfire is consistent enough now that it happens every time the car is up to temp.

Things I've done / tried:
-MAF, always seems to be an issue on these cars. I've bought two extras, as well as tried a known good one from a friend.
-Coolant temp sensor, the car has all the signs of a bad temp sensor, but replacing it didn't help. I took the little temp sensor sub harness out of the car today, looks fine, and continuity beeped at me. Assuming the wiring is fine.
-Igniter chip, bought one off of Zilvia, as well as tested a known good one from a friend. Still has the issue.
-O2 sensor, I bought one from a Baxter's auto. Connector is the same, it fits, but it doesn't look anything like the o2's I've seen in pictures. Though, I don't believe an o2 would throw me through this much of a loop. The car has the same issue with the old o2, new o2, and with it unplugged.
-TPS, ordered one in case I needed it, but the car goes from .45v at closed to 4.0v at wide open. I don't believe it's bad.
-Coilpacks, I bought 2 off Zilvia. I've tried every combination of the 6 total, and it doesn't make a difference.
-Plugs, I've done them twice. BKR6's, and BRK7's.
-Car has a FMIC. I figured maybe it's leaking, so I did the soapy water/look for bubbles method. I also sprayed carb cleaner around every coupler to see if I could get a change in revs. Halfassed, I know, but they don't seem like they're leaking.
-Fuel filter, more common maintenance, but I've seen them clog and give issues, so I went for it.
-ECU, popped a known good one in the car, same issue

I've given the IACV tube a pinch, and the idle drops. I can unplug it, and the car will hunt for an idle a bit, so I'm assuming its working.

The car has the same ugly misfire immediately after startup with and without the MAF unplugged. With and without the knock sensor unplugged. With and without the o2 sensor unplugged. With and without the coolant temp sensor unplugged.


TL;DR
I changed a bunch of things I thought would work, but I appear to be in over my head. Help. Please.

[blksylv]

Have you tried changing the cam angle sensor? I had the same issue a few years back and it ended up being the culprit

[Monica Blowinski]

No sir I have not. I've done some research on it, but I'd like to not open it up if I don't have to. Any way to test it before hand?

Edit: I found the FSM stuff on it. Removing it would require retiming the motor though, yeah?

[cbeuglas]

I have had a bad coil pack harness a couple of times, but engine temp should make no difference. Does not seem like a sensor to me. I have also had stumble issues with dirty injectors. At the same time engine temp should not matter.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[NiSilS14]

I've had a bad FPR once give me similar symptoms. It's usually associated with black plugs indicating the engine is running pig ass rich. Everything smells like raw gas too.

[LockOn!]

This may sound retarded but is your ECU plugged in and secured properly? I've had this happen myself where I was in a rush and the plug wasn't completely screwed down allowing some of the pins to wiggle. Resulted in intermittent stumbling.

I ran through practically your entire list before my buddy got down behind my kick panel and proceeded to fix my issue with 3 turns of a phillips screwdriver lol

[e1_griego]

^Had that happen to me, too.

[dorkidori_s13]

unplug your MAF and look inside the connector on the wiring harness. check to make damn sure ALL of the pins are making contact with the plug on the MAF itself. i had this massive gremlin of an issue haunting me for a over 3 years. car would have a lot of the same issues you described above... found out that a few pins inside the MAF plug on the wiring harness had completely flattened out and were making intermittent contact with the MAF when plugged in causing all sorts of stupid problems! wound up using a pick to bend them out a bit so they would stay in contact properly (a few weeks later i just wired in a new MAF plug harness)

[[email protected]]

start your car cold, when it's missfiring turn it off. check your sparkplugs. could be a sign of a leaking injector O-ring. obviously fuel pressure & coil packs are important but looking at what the sparkplug looks like during the missfire event will tell us a bit of information. if the sparkplug is fouled it's a sign of leaking injector O-ring or leaky injector. If the sparkplug has slight rust then it's water getting into your cyliners. My VG30 had a partially blown HG, where it wouldn't smoke or mix oil with coolant but every morning when i would start it it would missfire for a few minutes until it warmed up. this is my shot in the dark at your possibilities.

[Blk96t]

Make sure your intercooler piping is 100%. Get new couplers and t bolt clamps. This will save many head aches in the future.

Chech the coil pack harness connectors for corrosion. It usually occurs closest to the firewall. Also while you are there make sure the coilpack harness is grounded to the head. I've had both the problems and the car acted a lot like you are describing.
Once the car would get to full temp it would sputter and go into limp mode.

Another thing that helps a lot that has been my experience is have a good battery. For some reason when they start to go bad my cars start to act funny.

[Blk96t]

And both my sr's run like shit on cold start up. But come out of it after about a minute. Really annoying.

[Monica Blowinski]

I've had a bad FPR once give me similar symptoms. It's usually associated with black plugs indicating the engine is running pig ass rich. Everything smells like raw gas too.

I'll look into this. The FPR was sharing a vacuum line with the BOV/Wastegate at one point (I didn't do, I just fixed it..) so I wouldn't doubt it's not functioning properly. Car does run pig rich, and does smell of gas.

This may sound retarded but is your ECU plugged in and secured properly? I've had this happen myself where I was in a rush and the plug wasn't completely screwed down allowing some of the pins to wiggle. Resulted in intermittent stumbling.

I ran through practically your entire list before my buddy got down behind my kick panel and proceeded to fix my issue with 3 turns of a phillips screwdriver lol

I'll give it a tighten for shits and grins. The car has had this issue with 2 different ECU's, though. But, I'll look into it!

unplug your MAF and look inside the connector on the wiring harness. check to make damn sure ALL of the pins are making contact with the plug on the MAF itself. i had this massive gremlin of an issue haunting me for a over 3 years. car would have a lot of the same issues you described above... found out that a few pins inside the MAF plug on the wiring harness had completely flattened out and were making intermittent contact with the MAF when plugged in causing all sorts of stupid problems! wound up using a pick to bend them out a bit so they would stay in contact properly (a few weeks later i just wired in a new MAF plug harness)

The stumbling rough misfire with and without the MAF plugged in. The harness and MAF connector are both brand spankin' new and in good shape.

start your car cold, when it's missfiring turn it off. check your sparkplugs. could be a sign of a leaking injector O-ring. obviously fuel pressure & coil packs are important but looking at what the sparkplug looks like during the missfire event will tell us a bit of information. if the sparkplug is fouled it's a sign of leaking injector O-ring or leaky injector. If the sparkplug has slight rust then it's water getting into your cyliners. My VG30 had a partially blown HG, where it wouldn't smoke or mix oil with coolant but every morning when i would start it it would missfire for a few minutes until it warmed up. this is my shot in the dark at your possibilities.

I appreciate your shot in the dark. I did plugs maybe 20 miles ago. I'll go pull them in a few.

Make sure your intercooler piping is 100%. Get new couplers and t bolt clamps. This will save many head aches in the future.

Chech the coil pack harness connectors for corrosion. It usually occurs closest to the firewall. Also while you are there make sure the coilpack harness is grounded to the head. I've had both the problems and the car acted a lot like you are describing.
Once the car would get to full temp it would sputter and go into limp mode.

Another thing that helps a lot that has been my experience is have a good battery. For some reason when they start to go bad my cars start to act funny.

I pulled the coilpack harness out yesterday. All connectors look good, and nothing odd with the wires. Ground on the back of the head is clean and secure.

The battery in this car looks like it's from a lawn mower. It cranks the car just fine, but it's a little guy. Battery tray was cut into for the FMIC, so it's a half size battery. Worthy note, I reground/added a bunch of grounds around the engine bay.

Thanks for all the quick replies, guys.

[pacotaco345]

I would try the CAS, I know its already been mentioned but its a relatively easy and cheap check. My car used to have an issue breaking up real bad when in boost at partial throttle and I tried EVERYTHING besides the CAS first. Ended up being the CAS. Also, you don't need to re-time the motor although you should check your timing for shits and giggles anyways. Just put the motor at TDC then pull the old one, line up the dots and put the new one in.

[dorkidori_s13]

OH DUH!!! What fuel pump are you running?!

[Monica Blowinski]

OH DUH!!! What fuel pump are you running?!

I wrote this post out last night, and immediately ordered a new walbro last night.
I honestly don't know what pump is in it.

[dorkidori_s13]

I wrote this post out last night, and immediately ordered a new walbro last night.
I honestly don't know what pump is in it.

that MIGHT be your issue. i had my walbro go out on me last year, caused damn near everything youre describing (i had totally spaced this too)

[dorkidori_s13]

also, youll find out REAL quick when you change the pump if that was indeed your issue. its literally night and day if the pump was the problem!

if you have a fuel pressure gauge in cabin, you would instantly be able to tell if the pump was going out as fuel pressure would be jumping all over the place (even at idle it will cause lumps and back fires while taking off). i have a glow shift 3 in 1 gauge thats boost, fuel pressure and water temp, i am SO happy i invested in a gauge that included fuel pressure or i wouldve gone apeshit trying to diagnose the issue.

[lok]

Base timing seems off.

Since you have fixed most of your other janky issues.

Post a pic of CAS position.

[Kingtal0n]

need pics of engine. could be the maf is too close to compressor, hot engines speed the turbine, which whips the air around the compressor up into a frenzy when the bypass is shut (typically you remove the OEM bypass, this eliminates this issue because it hangs open at idle, but nobody runs the OEM bypass so...) thats why pics would help to determine pipe length/continuity. but everything else everyone said is also suspect when it comes to misfire.

I think you need a real boost leak test also, fill the plumbing with air pressure. Do not trust soap water / smoke or cheesy methods. Use a real boost pressure test. make sure you disconnect the crankcase breather line (valve cover -> turbo inlet) , if you fill the engine crankcase with pressure it could rupture an oil seal.