Misfiring intermittently during highway cruise

[steel_3d]

I'm a little bummed at the moment since my brand new engine is starting to give me the same symptoms as the previous one did when it blew the head gasket.

Basically I'll be driving on a flat highway at a constant cruise, or even downhill, and suddenly the car starts stuttering, misfiring. It's a very regular misfire like one cylinder stops firing completely. Letting off the throttle or giving it more gass, or playing with it in any way doesn't help, until I push the clutch in and let the rpm's drop to idle. Then I can go again for 5-10-15 seconds before I have to repeat. If I drive below 70 it seems to do a lot better and exhibit the problem much more rarely. If I go above 3000rpm the misfiring becomes more and more frequent. This only starts happening after a few miles of driving, when things are nice and warmed up.

Now given that this is the same problem I was having last year with the blown head gasket, requiring the same driving style, this is my theory: At higher rpm the water pump starts pushing coolant into the combustion chamber, eventually killing the spark. I'm assuming at idle there's much less water pressure and the engine manages to burn off whatever's in there and is able to fire again.

The problem seems to be more rpm dependent than load dependent. Usually when it's an ignition system problem, the issue occurs with higher load, but I have no problems accelerating as long as I'm below about 3000rpm, and if I'm above 3000 it misfires whether I'm accelerating, decelerating, or cruising.

I'm hoping you guys might have seen an ignition component failure that behaves this way, cause I can't really see definite signs of a blown headgasket, but it's probably wishful thinking...

I get no white smoke, no coolant loss or overheating, can't see fluid in the cylinders or on the plugs. On the other hand my plugs are white (o2 logs are iffy at wot, sometimes .94v, sometimes 80's, but at cruise and idle they always cycle nicely), and the logs show low timing at wot, like 15 degrees, sometimes tapering, sometimes rising. The knock graph on the other hand is not any different between a steady cruise or revving in neutral versus a wot pull with low timing. I'm using ecu+ so all I get is a spiky raw knock voltage graph. I was runnig 50% 100 octane, and only 8psi on a 14b for breakin, so I have a hard time understanding how I could have blown a head gasket. (I was still a moron for not taking the time to look through my logs carefully, just relying on the knock graph). This is a stock composite gasket with copper spray and arp's torqued to 85ftlb with lube, retorqued after a few heat cycles. Both surfaces were machined. The only questionable thing is that I put it on a 40 over bore. It wasn't quite sticking into the bore, but it was very close. Hope I didn't burn the fire ring.

Oh the only other weird thing that bears mentioning is that I advanced my exhaust cam 5 degrees and retarded the intake 5 degrees to get my FFWD 272's to idle nice.

Anyways, that's a lot of conflicting info, that's kinda why I'm throwing it out there, in case someone's seen the same thing before. I really don't wanna take the head off unless I'm sure. (No, I don't have any vacuum leaks I know this is a newbie forum, but please no newbie replies )

 

[JayRolla]

So it does have new wires and plugs right? Have you used a mechanics stethoscope to listen to the injectors. See if they are working?

How bad was the idle when you did the cams?? 272's should idle real nice at 750 maybe a little lopey. Your timing may be off?

Also when you did the HG did you blow the bolt holes out with compressed air before bolting the head on. Material can get down in there and cause miss readings on your torque wrench. Ive seen this cause HG's to blow.

 

[meliketoball]

Try the wires and things leading to that because they solved my misfire mystery problem.

 

[PieEyedPiper]

I can't comment on your cam and timing manipulation, but I have the EXACT same problem.

I've been fighting it for over a year now with no resolution. I finally ordered a new Cam Angle Sensor (CAS) and I am confiednt it will solve the issue. $43.

I'll post back and in previous P0300 threads with my results. The parts should arrive tomorrow.

 

[EvolvingGST]

which cyl is it coming out of? Have you tried the coil pack as well as new plugs and wires? And I would also say it might be an injector but I would say probably more to do with coil pack.

 

[jasteel13]

what motor setup do you have.. i see you have a 2g.. if you have a 1g CAS on a 2g head then i can bet that is your problem..

if that is the case you will need to switch to a 1g head... me and 3 of my friends had the same exact problem when doing the swap.. after putting on the 1g head.. no more misfire...

 

[talonalex92]

well, about a week ago i put some 92 octane in my 1g, and i got a horrible misfiring on highway speed/accel at highway. i filled up w my normal 94 and no more misfire. maybe you should try higher octane? good luck with it bro

 

[steel_3d]

New plugs and wires. Didn't check coil pack, power transistor or cas, they're the same ones the car ran fine with for a couple hundred miles before this problem started.

Can timing was set right and checked many times. The intake cam was maybe half a tooth retarded (nothing you can do to bring that back since the belt is rigid), but I retarded it way more anyway to make the idle smooth. It's known that regrinds aren't always ground on center, I'm chalking it up to that.

This was a full rebuild, so yes the block was machined and cleaned. Plus I'm using studs, they'll clamp no matter what.

How could I tell which cylinder is misfiring when it's only happening on the highway? I kinda doubt the injectors would be the problem since they work fine and the o2's cycle perfectly before the misfire starts. Also in my wot logs they can hit a nice rich .94v. All the plugs are uniformly white, no difference between cylinders. I should still richen it up to get the plugs to not be white. Then again they're new plugs, not sure how long it should take them to get colored with a proper mixture.

PieEyedPiper, do you REALLY have the same symptoms? Like you have to push the clutch in and let the revs down to idle before you can accelerate again?

The fact that letting off the gas doesn't clear up the misfire makes it unlike any other ignition problem I've ever seen, but if you are seeing the same thing that's great! I mean not great but together we should be able to figure it out (Jesus, a new CAS is over 400 dollars! Not that I would buy new. But I'd still rather pay 400 dollars than do a head gasket job right now )

 

[steel_3d]

1g head.

More than half the tank was 100 octane when this started. When that ran out I put in the normal 91 since that's all we get in Cali, and the problem is the same. Still, I've never heard of any gas causing misfires.

 

[PieEyedPiper]

New plugs and wires. Didn't check coil pack, power transistor or cas, they're the same ones the car ran fine with for a couple hundred miles before this problem started.

Can timing was set right and checked many times. The intake cam was maybe half a tooth retarded (nothing you can do to bring that back since the belt is rigid), but I retarded it way more anyway to make the idle smooth. It's known that regrinds aren't always ground on center, I'm chalking it up to that.

This was a full rebuild, so yes the block was machined and cleaned. Plus I'm using studs, they'll clamp no matter what.

How could I tell which cylinder is misfiring when it's only happening on the highway? I kinda doubt the injectors would be the problem since they work fine and the o2's cycle perfectly before the misfire starts. Also in my wot logs they can hit a nice rich .94v. All the plugs are uniformly white, no difference between cylinders. I should still richen it up to get the plugs to not be white. Then again they're new plugs, not sure how long it should take them to get colored with a proper mixture.

PieEyedPiper, do you REALLY have the same symptoms? Like you have to push the clutch in and let the revs down to idle before you can accelerate again?

The fact that letting off the gas doesn't clear up the misfire makes it unlike any other ignition problem I've ever seen, but if you are seeing the same thing that's great! I mean not great but together we should be able to figure it out (Jesus, a new CAS is over 400 dollars! Not that I would buy new. But I'd still rather pay 400 dollars than do a head gasket job right now )

Yeah man, I have documented this several times in other threads as well.
The only way to cure the issue is to take it out of gear, allow rpms to hit idle and then throw it back in 5th.
From the info you've given me this is the same issue.
Oh a btw, its $43 for a new OEM CAS. I've seen used ones on ebay for as little as $20. Gary at Mitsu Graveyard was going to sell me a used one for $45 shipped, but I said no thanks because I could just get a new one for a couple dollars more.
My shipment is supposed to arrive today (I purchased new splash gaurds and the CAS) I'll let you know what up, it's a 5min install for the CAS but I won't know till tuesday (highway driving) if it cured the random misifiring when cruising at around or above 3000rpm.

But as a disclaimer I have no idea how your 1g head will affect this. Are you using a 1g CAS too? I'm not sure if a 2g CAS would fit a 1g head.
On the bright side it is still likely a CAS problem and 1G CAS' can be had from $40 to $100.

 

[steel_3d]

Wow, now I'm glad I posted! Thanks a lot for the info man! Crossing my fingers for you

Yeah I see the 2g cas is cheap, 1g cas is a bit more expensive new. And no, I couldn't use a 2g cas.

 

[PieEyedPiper]

It also just dawned on me..
I was thinking about it when I got up this morning, and it popped into my head before I was fully awake even, haha.

You're running a 6 bolt in a 2g, correct?
There is a known problem with the 1g CAS and the 2g ECU. Some say it is likely that the 1g CAS isn't as precise as the 2g CAS thus causing the random misfire.
Most poeple solve this problem with the "black lid" or "hall effect" CAS sensor.

Check these links for more info
http://www.roadraceengineering.com/1gcasin2g.htm

http://www.dsmtuners.com/forums/showthread.php?t=215140&highlight=Hall+CAS

As mentioned in the links, this is not always a solution, but for some people it is. Does ECU + have an option to tell the computer to not look for random misfires like DSMlink or DSMchips do?

I can't believe we didnt cover this earlier

 

[steel_3d]

This is not a "random" misfire though as I understand it. This is total unrecoverable misfire Also, the car has run for quite a while with this CAS before and after the rebuild.

I'm having doubts about the CAS idea. I'm looking at my logs from this morning, and there's absolutely nothing changing at the time the misfire starts, other than the o2's dropping lean (which will always happen with a misfire), while before the misfire they are cycling nicely. I'm a little stumped. I was hoping to see dips in the RPM or timing advance logs if the cas was giving bad readings. Especially since ecu+ logs actual cas events at a relatively high 25 samples per second.

Are you logging your car? What do your logs look like?

I've attached a crappy capture of my log. Cross is where misfire starts. Steady cruise, steady everything.

http://i19.tinypic.com/339k6iw.jpg

 

[flyinghighlm]

Have you pulled your injectors and had them checked and cleaned...My buddy with a 95 GST 6 bolt would do almost the exact same thing. Took it to the tuner shop, he showed them his logs and what not, they hooked up to the car and found out one of the 550Cc injectors was not firing correctly. At idle it was fine, mid RPM the injector damn near shut off and at a cruise it was intermitant at best. So look into your Fuel Injectors is what I am saying and do not put 100% into your logs, he did and chased a ghost for 3 months.

 

[PieEyedPiper]

This is not a "random" misfire though as I understand it. This is total unrecoverable misfire Also, the car has run for quite a while with this CAS before and after the rebuild.

I'm having doubts about the CAS idea. I'm looking at my logs from this morning, and there's absolutely nothing changing at the time the misfire starts, other than the o2's dropping lean (which will always happen with a misfire), while before the misfire they are cycling nicely. I'm a little stumped. I was hoping to see dips in the RPM or timing advance logs if the cas was giving bad readings. Especially since ecu+ logs actual cas events at a relatively high 25 samples per second.

Are you logging your car? What do your logs look like?

I've attached a crappy capture of my log. Cross is where misfire starts. Steady cruise, steady everything.

http://i19.tinypic.com/339k6iw.jpg

"Random Multiple Cylinder Misfire - P0300" is the name and description for the problem we are discussing.
Don't rule out your 1g CAS + 2g ECU situation just cause it didnt happen before.
Your combination of parts are known to have this issue.

BTW, other than misfiring and your possible TPS issue (seen other thread) how do you like the stroker?

 

[steel_3d]

"Random Multiple Cylinder Misfire - P0300" is the name and description for the problem we are discussing.
Don't rule out your 1g CAS + 2g ECU situation just cause it didnt happen before.
Your combination of parts are known to have this issue.

BTW, other than misfiring and your possible TPS issue (seen other thread) how do you like the stroker?

I thought when people were talking about P0300 in 6-bolt swaps they were just getting the code but no actual drivability issues.

Sorry, I can't comment on the stroker yet, since it's never run right yet. Running 8psi on a 14b feels like running 8psi on a 14b Especially now that I adjusted my cam timing. I think it felt a bit stronger with the straight up setting, but I had to change that to have a chance at smog. Anyways the tune is so rough right now that I can't make a judgement. Building it was fun though Dealing with machine shops was not.

The real test will be to see if it spools the 3052 well enough for autocross.

 

[PieEyedPiper]

UPDATE!
As promised.

Before w/ old CAS: 1 25min trip on the HWY travelling 33miles would net me 1-2 Random Misfires. If I was lucky and good with the pedal, zero. If it wasn't my day as much as 5-7 Random Misfires.

After new CAS install: 4 total 25min trips on the HWY travelling 33miles netted me ZERO Random Misfires.

Conclusive? Not really. But if I make it 2 weeks with no code and no misfiring on the HWY I'll be extatic. By then it will be safe to call this issue fixed.

 

[steel_3d]

Great news man! I'm happy for ya!
Let us know if anything changes. Meanwhile I'll start looking for a CAS.

 

[PieEyedPiper]

Well I have an admission to make.
and frankly, I'm right pissed about it. The new CAS didn't fix my problem. I drove 100miles tonight and got 2 codes for P0300.

I've checked every related system and the CAS was the last piece of the puzzle. Its truly strange that I'm experiencing the SAME symptoms that 6 bolt users get, same rpm's, same code and same result. It seems Irony is not without a sense of humor.

I wish you better luck than I, my friend.
But do persue the CAS as it has been documented to be a significant part of a 6bolt swap.

(but if all else fails it looks like DSMLink might be our only way out!)

 

[steel_3d]

Fixed the problem! It was ecu+'s fault. Turns out when I flashed it with the new firmware it changed the CAS input setting to 97-99 internally, while in the software it was showing 90-94, making me think it was set correctly. Basically it was running the signal straight through, the way a stock ecu would see the 1g signal, which we know can cause the P0300 bug. Once I reset it to 95-96 and back to 90-94, no more misfire! The 40 mile drive to work was veery satisfying

So FYI, if anyone's considering ECU+, another benefit of it is that it can fix the random misfire bug with 6-bolts in 2g's. Also lets you run the 1g cas with the 95-96 ecu without messing with the coil pack wiring. Nothing dsmlink can't do, just sayin

 

[PieEyedPiper]

Glad you got it fixed.
Man, ECU+ looks appealing right now.

 

[steel_3d]

Ahhh this is bullshit, today the problem is back! I drove 80 miles yesterday, nowhere near taking it easy, with not a hint of a problem. Today it's back to the shitty misfire. I'm still leaning towards a firmware bug with that CAS setting. Back to the drawing board...

 

[PieEyedPiper]

haha.
Ok its not that funny.. (wonder how I'd know)

I've recently tried resetting the ECU with my new CAS to see if the computer needed to adjust to the new sensor so far no porblmes in 80miles. But I'll refrain from making any predictions.

Can ECU+ stop your ECU from even looking for a random misfire like DSMlink?

 

[steel_3d]

Nope, it can only condition the signal. I wish it was like dsmlink, it would be a lot easier to pass with all these emissions related codes that keep popping up.

By the way, my drive today was perfect again. ####in stupid

One weird thing about this bug that I've seen people mention is that it takes much longer to reoccur if the code's been cleared. Makes no sense logically. Unless the ecu's supposed to change its behavior based on codes.

 

[PieEyedPiper]

Poeple say that, but I've never experienced it. I can clear the code and have it retun in 2 minutes.
I think the two are unrelated.

Just drove another 120miles and no CEL or misfiring at all.
Agreed, this is pretty lame stuff.