WHY CAN'T I HOLD 15 PSI?!? Another dissatisfied, jaded KA-T owner.

[fiznat]

I tried this...there's definitely air flowing through this line, but pinching it shut (as best as I can) barely changes the RPMs the engine idles at (it lowers the idle by maybe 250 or so)...it still idles wicked high...But it certainly doesn't come close to dying.

Ok then there is no doubt about it, you definitely have a huge vaccum leak somewhere on your intake manifold, in or after the throttle body. This is why your idle is so high-- so you can basically stop looking at electrical stuff for now.

You must have done this a million times, but turn the motor on, let it idle, and run your bare hands all around the manifold. You wont feel leaks, but listen for idle changes as you run your hands around the surfaces. Pay special attention to the emissions stuff in the back, and the throttle body area. As you probably know there isnt much that can pinch/burn/shock you around there, so get touchy feely with the thing. You have a fairly large leak in there somewhere, it cant be that hard to find. It may help to do this while the IACV line is plugged, so that any vaccum leaks you plug up will drastically effect the idle. Also like WD said, make sure that the throttle plate is completely closed while you're at idle-- thats an easy space for extra air to be getting in. Dont just check the cables, look at the plate itself and make sure its shut and sealing.

If NONE of that works (and really, it should)-- just suck it up and take the freaking intake manifold off, rebuild it, and put it back on so that you can be sure it is 100% airtight. Like I said it cant be more than a 1 day job so if you get to this point just suck it up and do it.

Good luck man!

[Warped]

Smoke maching, get one at walgreens. Should have one for haloween for pretty cheap fill your engine bay and start it should see the leak .Worked for me a couple of months ago

[WDRacing]

spray the entire motor down with brake cleaner or wd40 while its running, the idle will change when you hit the spot with the leak.

[tiger]

hey i know your frustration, i hate it when something happens to my car and I can't figure it out, it stresses me out SO bad. When I finally figure out what's wrong I feel like doing cartwheels and backflips i'm so happy. I wish you luck in finding out what is wrong with your car,

tiger

[fiznat]

Put your entire car underwater mark-- where you see the engine sucking water into the intake manifold then you've found your spot!

[Florida240sx]

Roflamo fiz. just saw a tuck underwater due to him forgetting to put it in park while trying to load his boat.

[MarkEmark]

UPDATE:

Figured out why the car was idling at 3000 rpm, and it was a very simple, easy fix...should have been the first thing I checked.

The throttle body stop was hitting part of the T-bolt clamp for the silicone coupler that goes over my throttle body...the reason I didn't think there was any obstruction was because when you lifted the throttle body valve up and down, it made a click when it got to the top, and a click when it was "closed"....and after I disconnected the throttle cables and the TPS, and it still idled at 3000, I ruled out the throttle body being open a little bit. But sure enough, it was, and literally by about 1/16", which apparently is enough to bring it up to 3000 rpm at idle.

Anyhow, i took the car out for some tests. I connected a very accurate mechanical boost gauge to the turbocharger compressor outlet (at that vacuum elbow), so I could see what the difference in pressure was between the pressure at the turbo outlet and the pressure in the intake manifold (which my regular boost gauge gets its source from). At 0 psi according to the IM boost gauge, the turbo boost gauge read 6 psi +...even when the IM boost gauge was still in vacuum and I was only on the gas a little bit, the turbo boost gauge read 4 psi or so....hmmm. However, WOT, the IM boost gauge read about the same (1 psi lower) than the turbo boost gauge.

So I brought the car back to test if it was my actual IM boost gauge that was faulty. I tested it compared to the mechanical boost gauge on the compressor outlet, and they both read identically (well, the IM gauge read 1/2 psi lower, negligible for all intents and purposes). So I know it's not the in-car IM boost gauge that's faulty.

With the wastegate actuator getting its boost source from the intake manifold, I couldn't boost past 6 psi when the wastegate was connected, even though the wastegate is a GReddy 14 psi unit. It'd boost to 10 psi for a second and bounce right back down to 6 psi and remain there pretty solid. So I tested the wastegate actuator. And sure enough, it opened EXACTLY at 14 psi, no more, no less. So the actuator works perfectly, and so does the boost gauge that's recording the pressures I'm at.

So I disconnected the wastegate signal line and took the car out. I was able to hold 15 psi to 6000 rpm in 2nd and 3rd gear (part throttle, NOT full throttle), according to the boost gauge connected to the turbo compressor. When the boost gauge connected to the compressor was reading 15 psi at 6000 rpm, the one connected to the intake manifold was reading ~ 2 psi.

WTF!

This just verifies what I already knew: there's a substantial leak in the intake manifold, causing a huge discrepancy between the boost the turbo initially makes, and the boost that the engine actually INGESTS. There are 2 boost leaks I know of in the intake manifold: one from the EGR valve, and one from the EGRC-BPT valve.

When I have time (and motivation) I'm going to remove all of the EGR crap and plug the hole in the intake manifold with a block-off plate. If that doesn't solve my problem, then may God have mercy on my soul.

The good thing I learned today is that my turbo has no problem holding 15 psi to 6000 rpm in multiple gears....and that's exactly what I want it to do, but unfortunately, I want it to hold 15 psi at the INTAKE manifold, NOT the compressor.

[huguetpj]

When I have time (and motivation) I'm going to remove all of the EGR crap and plug the hole in the intake manifold with a block-off plate. If that doesn't solve my problem, then may God have mercy on my soul.

GO FOR IT!!!! You want motivation? Unfortunately I don't have a pic of my friends face's yesterday when I took them for a ride @ 14PSI... there is really no more motivation than that... well there is... my own face

Quote »The good thing I learned today is that my turbo has no problem holding 15 psi to 6000 rpm in multiple gears....and that's exactly what I want it to do, but unfortunately, I want it to hold 15 psi at the INTAKE manifold, NOT the compressor.[/quote]Good progress your making there. And just a few days ago you were about to give up, weren't you? We've all been there... it just takes patience and time.

Good luck.

[MarkEmark]

Yeah I scared a few of my friends when it was running at 15 psi (but then dropping to 10 psi). I figure running at a full 15 psi across the rev-range will freak a lot of my friends out lol.

Off-topic: you made ~340 whp @ 14.5 psi...those are VERY nice numbers, and that's exactly what I'm shooting for (330-340 whp, will probably be more like 17 psi though). What's your set up? Do you have a website?

[WDRacing]

Awsome Mark...well kinda. Atleast you fixed one damn thing...lol. I just took my car on a 15 psi run with no problems. First run of this kind in A LONG time. I'm running out of fuel pump at 15 psi. So it's time for the alky.

Best of luck with that awful friggin intake.

WD

[huguetpj]

Off-topic: you made ~340 whp @ 14.5 psi...those are VERY nice numbers, and that's exactly what I'm shooting for (330-340 whp, will probably be more like 17 psi though). What's your set up? Do you have a website?

Since this is your thread... and I do love talking about my car ... I think we can get a bit out of topic.

340 with a bad case of spark blow out, yep. I closed my plugs and the car now holds 15PSI no issues, so I'm hoping to increase those numbers a little... although I don't know how much closing the gap is going to affect my numbers. Just need to reach 18PSI before going to the dyno again.

I had a website... but I believe it's still down. Haven't been able to get web space for it.... anyone? But my setup is T3/TO4E .60A/R-60trim, 550cc RC eng injectors, emanage, 300zx MAF, nology wires (installed after dyno), nology coil (installed after dyno), and that's about it for power mods.

[MarkEmark]

A bit of an update (again). Please don't lose interest in the thread guys, the problem is still just as bad as ever, and if I don't get this thing running right before I head down to North Carolina the end of August for school, I'm going to be very disappointed.

For those of you just tuning in: The car boosts quickly to 15 psi (or 10 psi, whatever I'm at), and then IMMEDIATELY drops back to 10 psi (if it were originally 15 psi), or to 5 psi (if it were 10 psi). The gauge just hits 10 and literally bounces back immediately. "peak" boost is only there for a fraction of a second.

A while ago I hooked up a boost gauge to the compressor outlet to compare to the boost gauge at my intake manifold, and the one at the compressor outlet showed a lot more boost than the one at the intake manifold, leading me to believe that there was a substantial leak in the intake manifold. Now, I don't believe there's a leak in the intake manifold, or if there is one, it's NOT big enough to cause the problem I'm describing.

I bypassed the intercooler, thinking perhaps there was a flow problem with the intercooler or one of my pipes...so I ran the car with no intercooler. Did the same thing, hit 10 psi, bounced right back to 5-6 psi.

Then I hooked up a boost gauge to a spot on the cold pipe RIGHT BEFORE the throttle body (intercooler connected). Compared it to the boost gauge on my intake manifold: they were IDENTICAL, that is, both gauges hit 10 psi and bounced back to half of that. This rules out any leak in the intake manifold as being a problem...because if there were a leak in the intake manifold that was causing such a boost loss, the gauge hooked up to the intercooler pipe would read 10 psi the whole time, whereas the gauge at the intake manifold would read 10 psi and then bounce to 5 psi (from the "leak" in the intake manifold). This is not the case, which actually makes me a bit happier....no need to hunt down a non-existent leak in the intake manifold.

So there you have it guys. It's NOT the intercooler piping (I've bypassed it and it did the same thing, and I pressure tested the intercooler/piping and there were no leaks). It's NOT the BOV. It's NOT the turbo wastegate (it opens up at 14 psi exactly, i already tested it). It's NOT a leak between the turbo manifold and the head (all new OEM gaskets there, every nut is torqued down).

The problem has to be something with the turbo...I've suspected that I perhaps have blown seals (evidenced by oil collecting in the turbo inlet pipe) and have not run a restrictor in the feed line until a week ago.

But what's downright WEIRD is that when I had a boost gauge connected to the compressor outlet, I was able to get 15 psi all the way to redline with the wastegate signal disconnected (NOT WOT, otherwise I wouldn't be able to regulate the boost).

So here's my question: would bad turbo seals cause the boost drop-off described? The turbo is small (T3 Super 60, .48 a/r turbine, .60 a/r compressor), but not THAT small, and I know many people run straight T3's that hold 10 psi to red-line.

I'm stumped...I thought the fact that I got 15 psi up to redline by carefully regulating throttle input ruled out the turbo not being able to build boost....but it HAS to be something with the turbo.

I wish someone locally had a turbo that was functioning perfectly so i could test theirs out (*cough* foster *cough*)....

Also, interesting to note is that I'm running aftermarket cam shafts, which are more aggressive than S13 cams. They are PDM stage II DOHC cams, and they were designed for natural aspiration. But I've asked Don before if these cams would have any damper on performance if the engine were turbocharged, and he assured me that they wouldnt.

These are the specs for my cams:

Intake 221 duration @.050” .379 lift; (272 advertised duration), .380 lift; Exhaust 231 duration @ .050" lift, (278 advertised duration), .390 lift.

These are the specs for the PDM stage II DOHC TURBO cams. They seem to have very similar specs, minus the duration, of course. But could that much more duration cause the described symptoms.

STAGE II DOHC Turbo Cams – Intake 221 duration @.050”, .380 lift Exhaust 221 duration @.050” .380 lift

Basically, they're identical to my cams except that mine have 10 degrees more overlap on the exhaust cam. Would 10 degrees more overlap cause an instant 5 psi loss like that? Perhaps?

Any ideas?!?
Modified by MarkEmark at 2:38 AM 8/8/2005

[tiger]

do you have a boost controller?I had a boost controller on my SR and when I didn't hook the vaccum lines up right it would do that kind of stuff, peak and then drop off... the lines were kind of backwards.. i had pressure and vaccum mixed up i guess.

[MarkEmark]

do you have a boost controller?I had a boost controller on my SR and when I didn't hook the vaccum lines up right it would do that kind of stuff, peak and then drop off... the lines were kind of backwards.. i had pressure and vaccum mixed up i guess.

It has nothing to do with a boost controller, if you read the rest of the thread (I doubt you did, and I don't blame you!). I don't even have a boost controller right now. The wastegate line is hooked to a pressure source on the intake manifold. It's not a boost leak. I've determined that.

It's either my turbo that's causing it or my high overlap, long-duration exhaust cam....or something else that I don't know about. But I'm not stupid enough to have overlooked obvious things like an MBC hooked up incorrectly...it could very well be my cams, I just hope it isn't, because they really do aid quite a bit in making the KA head flow, along with oversized valves and a 3 angle competition valve job. However, if it is the cams, I'm sure I'd have no problem having someone give me their stock cams and cash for mine.

[crzycav86]

Then I hooked up a boost gauge to a spot on the cold pipe RIGHT BEFORE the throttle body (intercooler connected). Compared it to the boost gauge on my intake manifold: they were IDENTICAL, that is, both gauges hit 10 psi and bounced back to half of that. This rules out any leak in the intake manifold as being a problem...because if there were a leak in the intake manifold that was causing such a boost loss, the gauge hooked up to the intercooler pipe would read 10 psi the whole time, whereas the gauge at the intake manifold would read 10 psi and then bounce to 5 psi (from the "leak" in the intake manifold). This is not the case, which actually makes me a bit happier....no need to hunt down a non-existent leak in the intake manifold.

I may have spotted a flaw in your test here. At WOT, the pressure in the manifold would be nearly the same as the pressure in the cold pipe because there's no restriction big enough to cause a massive pressure drop. I just don't see how the test proved that there's no leak in the manifold.

[MarkEmark]

I may have spotted a flaw in your test here. At WOT, the pressure in the manifold would be nearly the same as the pressure in the cold pipe because there's no restriction big enough to cause a massive pressure drop. I just don't see how the test proved that there's no leak in the manifold.

The pressure would be the same in the IM and cold pipe, ASSUMING it's a closed system and there was no boost leak in the intake manifold. I'm not referring to restrictions; I'm referring to leaks, which everyone here, including me, thought I had.

If there were a leak in the intake manifold, the pressure at the cold pipe would be higher at WOT...my boost gauge in the car is hooked up to the FPR line, which sources from the back of the intake manifold. If there were a leak in the intake manifold, the boost gauge on the intake manifold would be reading lower than the boost gauge on the cold pipe, while the gauge on the cold pipe would remain constant.

I'm nearly positive the drop off has nothing to do with any leaks...after all, I fixed 4 leaks and noticed not a single increase in pressure at any RPM...little leaks do NOT cause such a rapid boost drop off (5 psi in a matter of 100 rpm). For that much air to be bled off with regards to how much air the turbocharger is pushing, a hole the size of my finger would need to be present.

Right now I believe it's the turbocharger, or camshafts. And no, it's NOT my timing; the cams are correctly degreed, the engine was professionally assembled, and I made dead positive the car was at TDC of the #1 when I put the distributor in. Nothing's off.

Of course, the only way to tell is to test. Hmm....I wonder if anyone in the CT area just blew up their KA-T and could let me borrow their camshafts and/or turbo for a couple of days...

[Jookmasta]

this has turned from a mission into a war. i think u should still pull off the intake mani to deal with the EGR valve. granted there's a slim chance of it fixing your issue, might as well sit down and do the project since when school starts back up, u probably wont have the time for that. as for ur turbo, i was not aware that you are running a str8 T3. i know that with my str8 T3, i have to kinda feather the throttle so that the boost isnt made too quickly on a hot day when the engine is warmed up or i will hit the 12 pounds and then drop back to like 9 and then back up to 12. u dont have any lag correct? also i wish i could let you use my turbo to see whats up with yours cuz we have almost identical turbo specs. o well. good luck with it, again.

[huguetpj]

The pressure would be the same in the IM and cold pipe, ASSUMING it's a closed system and there was no boost leak in the intake manifold. I'm not referring to restrictions; I'm referring to leaks, which everyone here, including me, thought I had.

Once the TB is opened, both the intake mani and the cold pipe become a single volume, meaning that any leak be it at the cold pipe or intake mani would affect both readings. So your test proved nothing, sorry to say. Now, if you have a leak at the intake your vacuum @ idle would suffer... unless something is opening under boost and closes itself under vacuum.

Have you check the brake booster check valve? Dunno if that could cause it.

Personally, I would fix/remove the EGR stuff, but I know how you fell on pulling the engine and stuff like that. Anyway, a leak should prevent you from reaching boost as fast as with no leak... but I don't believe that the turbo can peak and then fall off due to a leak. If you can reach 15PSI and then it drops off... I'm betting that you are flowing too much for that turbo... and the PDM cams may be hurting you in that aspect since the car is breathing better meaning the turbo must work harder to give you the same PSI.

[MarkEmark]

In any case, I still highly doubt it's a boost leak at this point. Like you said, it just doesn't make sense...hits 15 psi or 10 psi or whatever real quick and then quickly drops off. And like you said, a leak in the intake manifold would make the vacuum whacky at idle, unless something is opening only under boost and closes under vacuum (doesn't seem likely).

The brake booster check valve is something I was thinking about too....I'll check it, although I've never heard of this check valve failing?

The cams could be the problem, but honestly, I don't think 10 degrees more overlap is causing this problem...not to mention, it'd be a PITA/costly to swap them out (i'd need to re-shim all of them, again...).

Honestly, at this point I think it's the turbo...all that I need is a T3/T04E to test it out on my engine...I have a feeling it may eradicate the whole problem. I know Foster has his T3/T04E sitting around unused at this point, I'll ask him if I can borrow it/his downpipe or just the turbo for a day. Hell, I'll even pay him and pick it up and return it to him.

I should go ahead and check out the EGR valve, but I have the EGRC-BPT valve completely removed right now and all of the lines going to the EGR plugged too. And when i was pressure testing the whole system it was a very very small, slow leak out of the EGR valve, DEFINITELY not enough to lose 5 psi in a fraction of a second, not considering how much air that turbo is flowing.

Right now I want to test out at T3/T04E, and if that's not it, then there's only one other possible thing, and that's the camshafts, because theres no way I'm losing 5-7 psi out of that EGR valve.

[huguetpj]

I don't mean to say the cams may be the problem. What I meant to say is that you are flowing more air than somebody else with OEM cams so you might be chocking the turbo while somebody else with the same turbo but no cams might not.

Hopefully you can test out with another turbo... with a bigger A/R to see.

[Warped]

basically the turbo cant keep it at 15 psi because your cams are to efficient for the turbo
Modified by Warped at 2:40 AM 8/9/2005

[dft24ds]

ther is a guy on here selling a t3/t4 in CT whats his name...afmafia...check it out maybe he will let you run it on your car for a day or so to see if that fixes your poblem its in the nissan parts forum

[SSS]

basically the turbo cant keep it at 15 psi because your cams are to efficient for the turbo

Modified by Warped at 2:40 AM 8/9/2005

That makes no sense whatsoever.

Mark, you can rule out your cams. The 10 degrees less overlap for the turbo cams is to reduce the amount of fresh intake charge that gets passed through to the exhaust when both valves are open.

[crzycav86]

Actually it's to reduce the amount of exhaust that'll be pushed back to the intake. The pressure on the exhaust before the turbo is greater than the pressure of the intake charge, I believe.

[SSS]

That is correct for NA motors, however at any given pressure level in the intake manifold, the back pressure in the exhaust manifold before the turbo will always be slightly less; that is of course unless the exhaust manifold is a POS and/or the wrong turbine housing is selected for that given engine.

[C-Kwik]

That is correct for NA motors, however at any given pressure level in the intake manifold, the back pressure in the exhaust manifold before the turbo will always be slightly less; that is of course unless the exhaust manifold is a POS and/or the wrong turbine housing is selected for that given engine.

That really depends on turbo sizing vs the application and boost level. Turbos running at higher efficiencies will tend to have lower backpressure. Overworking a turbo can create a very high amount of backpressure.

[C-Kwik]

Mark, I'm Curious(and lazy). How did you pressure test the piping? And at what pressure?

[MarkEmark]

Mark, I'm Curious(and lazy). How did you pressure test the piping? And at what pressure?

I used a portable air-compressor from home depot (my big in-garage air compressor broke down a few months ago) and just plugged some of the hoses and pressurized it through my BOV (the internals removed). It was a crappy air compressor. I tested the intercooler/piping to 15 psi no leaks, i didn't get the whole engine past 6 psi. But I really don't think it's a boost leak at this point...when I had the whole engine to 6 psi, it took a good 30 seconds after the air compressor to turn off before the intake manifold was completely de-pressurized...and with a turbo pushing a lot of air, this small of a leak would not make a difference.

Of course, the problem with pressure testing everything when the engine is off is that I don't know how it ACTUALLy reacts when it's running, especially in regards to the EGR system. If you've ever taken a look at the vacuum diagram for the EGR system, it's absurdly complicated.

I dono, I pretty much give up. I'm in North Carolina the 27th and am working up until them. I have neither the time nor the will to work on it. Guess I'll just need to wait until my next break...I just wanted to try out a larger turbo and see how it worked, but that's probably not going to happen either. Oh well. It was a crappy, crappy summer anyway, this just made it a tad bit worse.

[WDRacing]

I hear ya with the crappy summer Mark...I'm seriously debating putting mine up forsale and going back to domestics. I'm actually driving up to Tempe AZ this weekend to look at a nice 86 Monte SS. The fact that I can replace the entire rotating assembly on a 350 for the same price as almost any turbo part for a 240 has me pretty much convinced.

Sorry we couldn't get yours fixed.

[turbo_lover]

umm... maybe coupling's with holes? not too sure though. just an idea.[ BTW - i wouldnt run non-intercooled on the motor cause it equals= cracked sleeves=overheating problems=loss of compression=more turbo lag... but you have a intercooler so nevermind me. ]