dead cylinder at cold start

[eh?]

I have a rebuilt rb25det that has been having a cold start problem in #6 cylinder. The cylinder will be dead until the engine starts to become warm. about 4-5 minutes. Here is what I have done with no help:swapped coilschanged plugschanged injectorcompression tested okJiggled fuel and coil harnessesI did reused the intake manifold gasket, it was on another motor for a few runs. All my troubleshooting is now pointing to that gasket. Can it be the cause of the misfire? TIA

[NISTECH]

yes it can as the cyl will be to lean to fire. the reason it goes away once warm, probably not etirerly though, is because the metal is expanding as it heats.

[eh?]

I removed the plenum and the gasket looked good. I sealed with with red RTV and reinstalled the plenum. No help.I recently installed a wideband and when it's cold and missing the AFR reads ~13. when the engine becomes warmer and the cylinder comes to life the AFR lowers to ~11.8 and when fulll warm after driving it will raise back to ~14.7.Can it still be the gasket?

[NISTECH]

Yea it is possible.Keep in mind I have never worked on an RB engine but the concept of a 4 stroke engine applies here. I have to ask though can the coils be plugged in at a different cyl? I would think so as you can do it on any of the USDM engines. If so try swapping coils between 2 of the cyl. see if the problem moves to the other cyl. if so you know its a coil. Also before you do this do a compression test cold and hot. See if there is a significant difference in the 2 readings. If neither of these find your problem you need to check for injector flow and spray pattern cold, this is if these injectors are removable independantly. One more question. Does the RB engine use an o2 sensor for fuel control? This might explain the fuel ratio readings your seeing as the o2 does not function till it warms up. At that time the fuel map is based on coolant temp and airflow readings.

[eh?]

I swapped the #5 and # 6 coil- no helpI r/r #6 injector with a new one, so spray pattern should be good. I didn't see an clogging in the fuel line.Yesterday and today were warm so it didn't miss at idle except if i revd it. I'd rev it to 2000rpm and let it drop where it missed for ~30 seconds.Now here's another finding. After a hard run shifting to 3rd gear when full warm (80+c) the engine will miss for about ~15 seconds. If i play with the throttle it will stop missing sooner. This has only started today. One i did not mention is for about the first 5 seconds at cold start up it will not miss. Yesterday I changed spark plugs, insulated coils with tape and torqued the head bolts to 100ft/lbs. Today I reinstalled the Blow off valve return hose. So now i have more power after a shift.

Oil consumption is good- none added in 600 miles. Hot compression on al six cylinders was ~140psi, lower but within tolerance of each other. I will do a cold compression test soon. #6 spark plug was black sort of sooty while #1 was whiteish/red.

So my main clues are: First 5 seconds will run on all cylinders (when cold outside)When warm outside, it won't miss until rev'dWill now miss after a high rpm 2-3 shift (due to leaner mixture/more power)No oil consumptionOk compression

I'm at a total loss.

[NISTECH]

The black sooty plug suggests its rich in that cyl.

[NISTECH]

I am going to move you to RB forum as those guys know more about this engine then I and may know whats causing your problem. i will still be monitering the thread.

[goofynick6]

One of the first things everyone should do is make a boost leak tester and use it...solves a LOT of problems.

Nick

[eh?]

if it's a leak it's a post TB leak, since it's at idle. Also, a leak would make you run lean no? Then why is the #6 plug sooty? As if it runs rich. But yes I do plan to make a leak tester, except i will make a plate to block the exhaust manifold outlet.

[Carl H]

do you have a s1 or s2 engine?perhaps its ignition related like a faulty powertransistor or a coil not firing until its up to temp.if you have a s1 engine you could try a new ignitior but if you have a s2 im not sure what you can do but convert the engine to an ignitor engine.ive heard of weird things happening when the ignitor goes bad, perhaps that is the root cause.

[goofynick6]

When I blow off an intercooler pipe, it runs really rich, like 9:1 on my wideband, even tho it seems it should run lean, mine was running rich and perhaps yours too. Make a $5 tester and try it out.

Nick

[eh?]

I have a SII harness on this engine. I swapped coils and taped them. Shook all wires. No help. This is were my AFR's are at:"I recently installed a wideband and when it's cold and missing the AFR reads ~13. when the engine becomes warmer and the cylinder comes to life the AFR lowers to ~11.8 and when fulll warm after driving it will raise back to ~14.7."

[yellow_jacket]

yes it can be. As the motor heats up and things expand, it will close the small leak and thus the miss will go away. Take some carb cleaner and spray it around the intake manifold where the manifold meets the head on the number 6 cylinder( or whichever has the misfire), if this changes the way the car is running, you know you have a vacuum leak in that area.

[yellow_jacket]

I don't know how I missed all of the replies above mine, but try finding the vacuum leak using the carb cleaner. You will also want to have a fire extinguisher handy.

I would also look at the injectors. It is possible that you have a leaky or dirty injector on number 6.

[Imissmyturbo]

My SII motor does this but only if the car sits for serveral days. And I haven't noticed it much with the weather warmer out. The best way to check for a leak is with a fogger. There should be a local garage that has one. It's a quick and easy was to find vacum leaks in the intake as well as the charge piping.

[JonPowell]

If there is a boost leak then the ECU will add fuel to compensate for air that no longer exists in the intake tract, thus going rich, not lean.

At idle the turbo is STILL sucking air into the intake tract, albeit at a very low volume. The engine could be sucking in less air than the turbo is sucking through the MAF also causing a rich condition.

Same thing happens with atmospheric BOV's!

[NISTECH]

Remember guys his problem is isolated to only one cyl. If it where a condition having to do with anything before the #6 runner on the intake it would effect all cyl's. Any measureing device meausures all air going into the engine, not just the air going into Cyl 6.

[NISTECH]

The igntor if like a Z could be the problem as mentioned above. If you had a multi pin ignitor you could have a poor connection with the terminals for #6 coil. I dont know how the ignitor is set up on the RB26 but like I said if each coil is independantly controlled like the VG30DE in the Z32 that could very likely be a problem.

[yellow_jacket]

my series I ignitor has 7 in, 6 out. They are labeled I1 through I6 so I would assume that they are individually controlled. It wouldn't hurt to check for corrosion on the pins and check for faulty wiring. I don't know what the Z uses to compare it to though.

[NISTECH]

sounds just like a Z, black box with a connector port at either side, about 4 X 4 inches square.

[goofynick6]

I'd just do the boost leak test, it'll probably show a leaky injector o-ring or something to that effect.

Nick

[eh?]

#6 o-rings were changed when i changed the injector, i have sprayed carb cleaner with no findings. This RB doesn't have an ignitor like VG30DE's or VE's. it has 6 individual ignitor/coils.

Hope to get a Intake gasket this week so i can eliminate it. I will leak test this week.Edit:Cold compression on 1&6 are 125 psi. Cold AFR's read 15.6 down to 13.3 warm. When i tap the throttle AFR's go to 17.8 and #6 misses. When #6 comes to life the AFR's come back down to 13.6.

Edit 2:

Nisstech: have you ever had a problem where a freshly milled head would cause the intake manifold to sit improperly, causing a leak?

Modified by eh? at 9:21 PM 5/20/2005
Modified by eh? at 1:10 AM 5/22/2005

[yellow_jacket]

Although I am not NISTECH, I haven't had any problems with the head being warped on the intake manifold side. It is possible though, but the head should be warped as well. I have had intake and exhaust manifolds be a little warped.

[yellow_jacket]

I just realized you had the head milled. Why did it need to be milled? Was it warped? Did they straighten the head before they milled it?

[eh?]

No the head was just refreshed, New seals, seal seat grind, etc. I asked them to mill to flat.

[biglipzit]

hmmmmmmmm any one suggested spark gap? Have you checked them at all? I had a miss on hard revs and idle and it ended up being that my plugs were gappeld be .8mm or if not someone correct me but check the spark gap it could be the prob.

[eh?]

I've used BCPR7EIX .8mm irdiums. I'm now using BCPR7ES gaped to .5mm. No diff.

[biglipzit]

then something isnt connected properly, maybe the injector plug or igniter plug but this has me totally stumped...

[eh?]

I've pretty much zeroed it to a gasket or the head/manifold mating surfaces. All wiring, etc are fine.

[eh?]

Changed Intake gakset- no helpPressurized entire air tract with 10 psi- no leaks.