Supercharged S14 Idle Issues and Power Loss

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TryingToTurbo
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Supercharged S14 Idle Issues and Power Loss

Post by TryingToTurbo »

Whats up guys. I am completely at a loss as to whats wrong with my car. Let's see if you can help.

Here's the run down on my build:

Built block (Done by me)
Wiseco pistons, Eagle rods, ARP head and main studs, Cometic HG, stock top end.
Eaton M62, Q45 MAF, S15 SR 480cc injectors, and NIStune.

Here's the problem. At idle, AFRs are super lean (past 18.0 AFRs) which is causing it to idle poorly with low vacuum (about 10 inHg) and sounds lopey. However, as I increase RPMs in neutral vacuum stabilizes as do AFRs from 2k and above. On the street AFRs are spot on at cruise and at WOT. But, it still feels like there is a loss in power at times, and other times it feels better.

Here's what I have checked. MAF voltage at idle is 1.125v and at WOT is 4.05v. No CEL except for EGR codes and IACV code. I don't have IACV or AAC or EGR. Fuel pressure is 43.5psi at idle. Plugs are new BKR7Es gapped at 0.028". Compression is 155-160psi across all four cylinders. Ignition timing is 20 degrees at idle. All vacuum lines look good. I only have 3: boost gauge, bypass valve, and fpr. I also have the brake booster line which is fine. O2 sensor voltage oscillates during cruise as it should. Coolant temps are fine.

The biggest kicker is this. This motor is freshly rebuilt by me. It has 980 miles on it since the rebuild. It drove perfect for 975 miles and then all the sudden it got like this. It used to idle fine, was good on power, everything. All the sudden one day it did this after a couple small pulls around town.

Any thoughts?
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Post by supakat »

The obvious is a leak. Pulling in air after the MAF on idle, but when no vacuum/boost the leak seals up. Maybe the rubber gaskets around the injectors. Sounds like something minor though.
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Post by TryingToTurbo »

supakat wrote:The obvious is a leak. Pulling in air after the MAF on idle, but when no vacuum/boost the leak seals up. Maybe the rubber gaskets around the injectors. Sounds like something minor though.
Not a vacuum leak. Here's the short and sweet. AFRs are lean at idle and it misses/rough idle. Vacuum reading is 10-15inHg at idle, but if I raise RPMs to about 2k, it smooths out, AFRs go normal, and Vacuum goes down to 20inHg like it should. So vacuum increases and it gets better. Opposite of a vacuum leak as described by you.

Thank you for the reply.
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Post by all shal perrish »

check your tps voltage, my setup was happiest set at .64v also, when i had a problem close to this, my watter temp sensor was going out at the same time, between the two, it was causing some annoying and hard to track down problems
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Post by TryingToTurbo »

all shal perrish wrote:check your tps voltage, my setup was happiest set at .64v also, when i had a problem close to this, my watter temp sensor was going out at the same time, between the two, it was causing some annoying and hard to track down problems
TPS voltage is 0.56v at idle which is where it's been at for the past 950 miles. I had no issues up until now.

Temp sensor is still reading fine as well on nistune and I believe it's new as well.
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Post by airman »

TryingToTurbo wrote:Not a vacuum leak.
Running lean at idle and only 10in-hg says vacuum leak to me :/

Done a boost leak test? Something mighta come loose.
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Post by all shal perrish »

whats your timing like at idle, it is possible your dizzy rotated and your timing took a dump, also,
have you done a compression test
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Post by supakat »

He mentioned that in his first post.
Compression is 155-160psi across all four cylinders. Ignition timing is 20 degrees at idle.
Watch the damn brake booster be the culprit. When the charger blows air, the one way valve will stop air making it run normal. But when it opens under idle, it is sucking un-metered air through the booster, hence a vacuum leak.
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Post by TryingToTurbo »

supakat wrote:He mentioned that in his first post.
Compression is 155-160psi across all four cylinders. Ignition timing is 20 degrees at idle.
Watch the damn brake booster be the culprit. When the charger blows air, the one way valve will stop air making it run normal. But when it opens under idle, it is sucking un-metered air through the booster, hence a vacuum leak.
I've had that happen before actually. I will plug the booster line and see what happens. Also I swapped dizzy and MAF with spares I had just for **** and
Giggles and no change.

The low idle vacuum and lean condition sounds like a vac leak too, but normal afrs in cruise don't make sense. Cruise is a high vacuum situation so it should lean out as well. Not to mention when I go to 2k rpms vacuum goes back down to 20inHg and afrs smooth out. That doesn't follow symptoms of vac leak either. I've tested the system to 20psi with no leaks using a cap in place of the MAF.

Edit: also pulled valve cover and timing is 100% there as well so I know it's not cam timing issues.
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Post by supakat »

Yea it sounds like a retarded situation. I have had some dumb sh!t happen to me in the past and I chased my tail. I have mixed feelings of this because when you cannot find the issue, you start worrying that it is a major issue or something leading to it but then when you find the solution and it is something minor, you laugh your @ss off and relieved it was something minor. Especially when you invested over a grand into the block.
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Post by TryingToTurbo »

supakat wrote:Yea it sounds like a retarded situation. I have had some dumb sh!t happen to me in the past and I chased my tail. I have mixed feelings of this because when you cannot find the issue, you start worrying that it is a major issue or something leading to it but then when you find the solution and it is something minor, you laugh your @ss off and relieved it was something minor. Especially when you invested over a grand into the block.
Yeah it's definitely something retarded. Like you said I was freakin cause I thought it was a burnt valve or something, but when compression was fine I didn't know what to check. All sensors check out and fuel pressure is good. Next on my list is boost peak test to 30psi, plug booster line, and check ecu for burnt traces. Other than that, I don't have a ***** clue????

Ps any of you guys run cometics? If so, did you retorque it even with arp?
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Post by supakat »

Nope. I did not re-tourque with arp and the lube.
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Post by TryingToTurbo »

supakat wrote:Nope. I did not re-tourque with arp and the lube.
Ok. Me neither. I didn't see any instructions to do so but just wanted to be sure.
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Post by BigLoukaT »

I had the same symptoms a little while ago, and the problem turned out to be the injector seals. It would run lean at idle, afrs would stabilize around 3k to stoich, cruising was decent, etc.

Boost leak tests are never a bad idea....

edit... i didn't see you already boost leaked to 20psi... good luck.
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Post by TryingToTurbo »

BigLoukaT wrote:I had the same symptoms a little while ago, and the problem turned out to be the injector seals. It would run lean at idle, afrs would stabilize around 3k to stoich, cruising was decent, etc.

Boost leak tests are never a bad idea....

edit... i didn't see you already boost leaked to 20psi... good luck.
Thanks for your reply. I will double check the injector seals as well. I'm assuming those are the thick rubber ones that seat the rail into the intake manifold that you are referring to?
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Post by supakat »

Which is what I stated above. I always RTV them.
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Post by klattr1 »

TryingToTurbo wrote: Not a vacuum leak. Here's the short and sweet. AFRs are lean at idle and it misses/rough idle. Vacuum reading is 10-15inHg at idle, but if I raise RPMs to about 2k, it smooths out, AFRs go normal, and Vacuum goes down to 20inHg like it should. So vacuum increases and it gets better. Opposite of a vacuum leak as described by you.
That is low vacuum for sure...sounds like there's a leak in the system somewhere (between the mafs and the supercharger inlet) since it's running leaner at idle now too. Pressure test the intake pipe. How many times have you reused the supercharger inlet gasket? What was your vacuum like at idle before? My black supercharged S14 was somewhere around 18-19 inHg at 800 rpms.
TryingToTurbo wrote: The low idle vacuum and lean condition sounds like a vac leak too, but normal afrs in cruise don't make sense.
If O2 is still connected, then O2 feedback will auto-correct (to a certain %) for any vacuum leaks in partial throttle situations...that's why it still runs the same as before there.
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Post by TryingToTurbo »

klattr1 wrote:
TryingToTurbo wrote: Not a vacuum leak. Here's the short and sweet. AFRs are lean at idle and it misses/rough idle. Vacuum reading is 10-15inHg at idle, but if I raise RPMs to about 2k, it smooths out, AFRs go normal, and Vacuum goes down to 20inHg like it should. So vacuum increases and it gets better. Opposite of a vacuum leak as described by you.
That is low vacuum for sure...sounds like there's a leak in the system somewhere (between the mafs and the supercharger inlet) since it's running leaner at idle now too. Pressure test the intake pipe. How many times have you reused the supercharger inlet gasket? What was your vacuum like at idle before? My black supercharged S14 was somewhere around 18-19 inHg at 800 rpms.
TryingToTurbo wrote: The low idle vacuum and lean condition sounds like a vac leak too, but normal afrs in cruise don't make sense.
If O2 is still connected, then O2 feedback will auto-correct (to a certain %) for any vacuum leaks in partial throttle situations...that's why it still runs the same as before there.
That gasket was torn around the bolt holes but is still sealing. The problem ended up being one of the welds on the intake lol. Where the inlet flange is welded to the 90 degree bend itis slightly oblong on the inside so there's on spot that was barely bridged by the weld and it cracked along the weld about 2" long.
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Post by nx2000det »

Nice to see you found the problem.
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Post by TryingToTurbo »

nx2000det wrote:Nice to see you found the problem.
Thanks, yeah it was tricky to find. I boost leak tested a second time using a new tester I made and thats how I found the leak. I got the pipe rewelded today and it's back to driving normal.

Thanks for all the input.
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Post by BigLoukaT »

TryingToTurbo wrote:
nx2000det wrote:Nice to see you found the problem.
Thanks, yeah it was tricky to find. I boost leak tested a second time using a new tester I made and thats how I found the leak. I got the pipe rewelded today and it's back to driving normal.

Thanks for all the input.
I know how you feel.... I chased my ass for a month before I realized that the brand new injector o-rings were leaking worse than the old ones I replaced, and were the source of my lean issue. oh well. It's nice to have a running car
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