HELP PLZ=ENGINE KNOCK W. I/C'd BOOST OVER 11psi

[Guest jjohart]

Hi,

I recently removed a "customized" pop off valve off my Z, when I realized it was wooshing/"popping" off at only 12.5psi. I have an 83 280ZXT with a Greddy Profec B boost controller, a NPR I/C and open air intake. I was reasonably happy with this set up, but I guess I got to thinking I should be able to run 12-15psi true (high or low boost settings on the controller). I also thought that the pop off valve was causing a bit of boost to be lost, and I didn't really want to mess with taking it apart to put in a higher resistance washer.

That said, the car seems to be struggling now even at low boost, oddly enough in second and third gears, with a kind of bucking you can feel, even though the boost needle is relatively flat (at around 12-14psi, depending on my settings). It is also causing an occasional knock (is this the same as detonation?), and certainly is of concern.

What do I have the mechanic look for? I have heard various folks tell me I need an aftermarket fuel management system (at least an adjustable fuel pressure regulator). Is this the most likely culprit, as I've been told an equal number of times that with just the intercooler and intake alone, my stock fuel set up should be enough. I'm just a little puzzled about this knock thing, and am also wondering if my "Faze" aftermarket boost guage underestimates boost levels (i.e when the stock Nissan boost gauge reads zero, the phaze shows it about -2...though I've heard that the Nissan gauge OVER estimates)! Please help, I don't want to blow this engine!!

Thanks

John

[jgkurz]

It's probably pre-ignition from running plugs that are too hot. Try the NGK BPR7ES or the even colder BPR8ES and gap to about .030. The -11 plugs are for gaps over .030.

[Guest jjohart]

Hi

no, I already WAS running cooler plugs!!!!

[Sean73]

I think 12-15 psi is way too much for the stock fuel system and stock fuel pressure. I don't think this level of boost is safe for your motor unless you have a wideband dyno to show otherwise.

 

If you follow conventional injector flow formula, the stock L28ET injectors are only good to about 11-12 psi in the realm of safe A/F ratios. I don't know who told you the stock fuel system is enough for 15 psi, but they are wrong! Everyone that I have seen on this forum running that kind of boost (consistently), have increased fuel pressure, at the least.

 

Knocking at 14 psi is not good, and could be potentially devastating. I think you should turn down the boost to about 8-10 psi low / high setting and see if the problem persists. If it persists at all boost levels, you might have a fuel delivery problem.

 

Sean

73 240Z Turbo

[Afshin]

What is the timing on your set up?. I would not keep it over 20 degree, more can easilly cause detonation even at 12 psi (when running stock EFI). Also as mentioned, 14 psi is too high for a completely stock fuel system and stock pressure.

[Guest jjohart]

Sean, et al,

I've done a couple of early evening runs with the car, both with identical settings, either high (15) or low (12), and I've found:

1. On the first run (after the car was fully warmed up), there was NO bucking/hesitating/knocking. I tried this on Rte 9 near Natick, MA, a 4 lane state road with lots of room to try and see if the motor would act up in 2nd, 3rd, etc, and it was faultless! I did about 5 miles of slowing down and goosing it, to no ill effect!!

2. The next trip, after the car sat for half an hour at Borders, was utterly different. From the moment I turned the key and drove gently in first and second gear, the car was stumbling...it seemed the cool down, while not complete (two to three lines on the engine temp, oil temp above minimum), had somehow unlocked the gremlins of a jalopy within my wheels! I swear, the more I pushed on the gas, the more this situation occurred..and this well before positive boost kicked in. I drove on, noting that the temps were in normal operating range, and tried rte 9 again, and found the same stumbling/bucking and eventual knocking as in worst previous descriptions (prev. post).

I am at a loss here. This car has had a really inconsistent response to conditions, and I've replaced injectors, battery, wires/cap/rotor, tuned it including "electrosonic injector cleaning". I'm using NGK stock Turbo 280ZX plugs, which are new...my Nissan dealer previously had 280 non turbo plugs in there, well before this condition. Finally, I"ve been using Techron or other fill up fuel treatments as well as 5 point octane boost with super unlead, so I don't understand how this can be a fuel (mechanical) problem, nor a plug cool temp issue (the car starts like a dream from cold)...I would hate to rule out the ECU, could this be producing a massively bad condition? How in hell can it be there on one drive, and then completely go away on the next, if all else is equal?!!!? ARRGGH!!

Am I better off getting into the JCW chip and injector set up (a massive investment for something that may or may not fix anything!), or doing this stage by stage, with the adjustable fuel pressure regulator first (CAN SOMEBODY PLEASE TELL ME WHICH SIZE FITTINGS AND WHICH BRAND WORKS BEST WITH MY ENGINE, IF NOT WHERE TO BUY?!!!?), and uprated fuel pump and the addtional expenses, if necessary of bigger injectors, fuel rail, etc (where in god does one get this?)?

Isn't there an ultra cheap way of crushing the stock fuel regulator...to boost fuel delivery a bit? Can anyone describe for a simple moron like me how to do this?

Thanks

John

[Guest bastaad525]

Yep you need more fuel. Stock EFI actually starts to run lean at 10psi WITHOUT the I/C. With it, I saw dangerously lean a/f ratios at even 8-9psi, above 5000rpm.

 

However, if I had to guess I would say the lean running does not have anything to do with the bucking you're feeling. Usually, this motor will actually run BETTER when running lean... it will feel faster. The bucking and such... is probably an electrical problem, or something else.

 

Before you do anything, before you add any more fuel or any of that, first turn your boost down to maybe 8-10psi. Then, get some dielectric grease from an electronic parts store, and a can of electronic connection cleaner from any auto parts store. Go thru and disconnect every connection of your wiring harness... the ECU, AFM, injectors, sensors, spray everything off with the cleaner spray, and then put dielectric grease on all of them and put everything back together, and see if this cures your bucking/stumbling. Alternately you can skip the dielectric grease and just spray them clean and see if that does it, but the dielectric grease would ensure you would not have to do this again for a LONG time (w/o it, I had to do this procedure about once a month). These old things love to corrode and can cause all kinds of gremlins when they do.

 

 

Hopefully this solves your problem, if not, there is something else going on there, maybe a bad sensor or afm, or maybe a short in your wiring.

 

I say figure this out first, before you go trying to up performance any more, just adding possible headaches as you add more variables to sort thru to solve the problem. Then add some more fuel and turn boost back up.

[Afshin]

first turn your boost down to maybe 8-10psi. Then, get some dielectric grease from an electronic parts store, and a can of electronic connection cleaner from any auto parts store. Go thru and disconnect every connection of your wiring harness... the ECU, AFM, injectors, sensors, spray everything off with the cleaner spray, and then put dielectric grease on all of them and put everything back together, and see if this cures your bucking/stumbling

 

Great advice, it's a must do, it causes this kind of erratic running all the time. Make sure you clean both ends (ECU and sensor) of every connector in the EFI harness.

[Guest jjohart]

Without debating the merits of the electronic spray cleaning, a very generalized service mechanic observed the condition, which IS NOT only on boost, but a bucking or flutter in any change of the throttle, especially when cold or restarted (sorry I didn't realize this was so far gone, and getting worse). The knock starts even at 8psi, so I am running the car at minimum boost, which up big hills means really feeling the unsteadiness of the power delivery anyway!

SO, the guy says it's the Air Sensor/AFM, which makes sense, in a way, b/c on one run this intermittent can disappear, stop and restart a few mins later and the same shenanigans play up. I have to be an optimist and hope that he's right, b/c a lot of the previous replies were complicated (1. HOW does one adjust the timing back of 20 degrees-what does that mean in laymans terms, and don't I need an oscilliscope or complicated equipment crap like that?!!?, 2. The guy who told me to gap the plugs couldn't even explain what he meant!!

THE REAL QUESTION-please answer here, so I don't have to post elsewhere, does anyone have a rebuilt or good condition AFM sensor for my purchase?!!? FAILING THAT, is it worth my time to open up the sensor and look at the flapper...even the Datsun service manual suggests, in every incidence of failure with the sensor (like using probes for resistance measurement, or flicking the vane!), to "replace the unit"!!

No one was able to tell me where to get an adjustable fuel regulator for this car anyway (or what brand/fittings/etc), so that'll have to wait!

As an aside, I'd love to go after the Jim Wolf/Ford Cobra sensor, but there's no way around having to spend 3 grand for uprated injectors and ECU, is there? I mean, I couldn't plug and play that with just an adjustable fuel regulator, could I?

Johjn[/i]

[Afshin]

A faulty AFM can cause your described problem, but more often it is a bad connection, so clean the connectors first and foremost

 

HOW does one adjust the timing back of 20 degrees-what does that mean in laymans terms, and don't I need an oscilliscope or complicated equipment crap like that?!!?,

Adjusting the timing is very simple, however if you don't know something as basic as that, than perhaps helping you online with any thing specific may be too difficult since it would require numerous tutorials on how an engine, EFI, ignition works and where things are located....

 

 

The guy who told me to gap the plugs couldn't even explain what he meant!!

Again, you do need a certain amount of background knowledge for effective communication on a forum. I would suggest you read a book or some articles.

How to adjust the gap on a plug, what ignition timing is and knowledge of basic tools (not complicated equipment crap like that, as you poorly put it). Don't blame the person who is not explain to you what an engine or ignition system is. You still owe them a thanks for trying to help you.

 

No one was able to tell me where to get an adjustable fuel regulator for this car anyway (or what brand/fittings/etc), so that'll have to wait!

Have you heard of the search function ?

 

As an aside, I'd love to go after the Jim Wolf/Ford Cobra sensor, but there's no way around having to spend 3 grand for uprated injectors and ECU, is there? I mean, I couldn't plug and play that with just an adjustable fuel regulator, could I?

Again do a search, I have no idea how you came up with 3 grand and no way to give a recommendation if you don't have any basic concept of a fuel injection system. You are actually asking if an adjustable fuel pressure regulator is comparable to a modified ECU, cobra MAF and larger injectors? Come on, that question is so far off base than IMO it does not deserve a response.

 

BTW, if you are wondering why I' going off on you, it's not that you just don't have a concept of what a car is. It's because you answer harshly and are critical of members trying to help you. Your tone suggest they it is our duty to fully explain everything to you as opposed to appreciating ANY and ALL thoughts that people take their valuable time to share. So unlike most members who post a thanks after getting advice, you have the nerve of complaining that you where not spoon fed (e.g. no one was able to tell me…, The guy who told me to gap the plugs couldn't even explain…..,. Furthermore, you don't know how to use the search function and you ask questions before thinking and doing basic research first.

Here is another example jgkurz said “It's probably pre-ignition from running plugs that are too hot. Try the NGK BPR7ES or the even colder BPR8ES and gap to about .030. The -11 plugs are for gaps over .030.†you responded: no, I already WAS running cooler plugs!!!!

Now IMO that’s plain rude. Your post asking for help did not give any info on what was done or checked on the car and then after using the word probably and giving good advice on cooler plugs, you responded harshly. Now since you like to be spoon-fed here is an example of an appropriate answer: thanks, good thought, but I forgot to mention that I already had new and cooler running plugs.

Get the picture ?

[Guest jjohart]

Well, Afshin, whoever you really are, I could go on about the basic ineptitude of your pedantic, patronizing and largely useless critique on my posts, but I find it hard to take from someone who can't afford to use their real name..not to mention taking a name which has no entmological entry in the English language (I searched Oxford), though it does have an entry under various baby forms of pre-English, aka pre-linguistic cooing/googlish! "Have you tried the feature called search?" How bout' trying alternate spelling, as in aft shin, which is where you ought to be kicked for your buggerhood!

On the other hand, being that you list as having a HIGHLY tuned Z, with much money on your hands and apparent arrogance of knowledge to boot in the most cosmopolitan city in the US, it is a pity you aren't empathetic enough to have ever had to push your car up or down some of those hills when it breaks down, and then have some show off hot shot (how bout' Sammy Hagar) giving you the bird from his 930, for not having a basic understanding of knowledge about "plugs, AFMs, gaps, etc", or whatever else beyond your understanding! You'd feel like letting your piece of handiwork roll off the hill and buy a Z..28!

I should not waste any time then, telling you you've made yourself like a pampered bitch in your post. I'd find someone with your anal-expulsions more likely driving a pink VW on North Beach, Bratz bobble-heds in the back window, than the car you apparently have your hands on (lucky doesn't always mean willing to straight talk what works, does it, or everyone would be doing exactly what you did...he, he, maybe you'd get your own cable show on Speedvision).

What do you think Hybrid Z is for, "Queer Eye for the straight Z"(?!!!!), so anyone expecting basic answers is instead berated by holier than thous chiming in such bits of overly opinionated technojargon, i.e "why don't you just spend $800 on esoteric fuel management set ups, oddball plug specs which won't let the car start in winter-thereby curing your stall outs, (heh, heh, heh!,) and which no one in your local servicing area (that is, for me, New England=California is known for more well prep'd "hot/wierd transport forms) will sell, support or do more than tell you to go back to stock from.

Why don't you go to the library and learn about why braggarts bone up on fuel management and racing terminology in one breath, and then tell you, when you use any semi-learned suggestion-i.e waste big bucks on intercooling, open intakes or other supposedly "bulletproof" add ons-to turn to others of more experience for HELP, you get "sorry, racing cars blow engines in one afternoon, what did you expect" or "eh, I'd like to help you, but it's better to wait til' your engine breaks so then you can find out what the cause is"!!

I made mistakes here, like running big boost numbers without fuel management, but do I have to visit with Marvin the Martian to get someone to surrender the information without getting blasted?!!!? It IS possible to get BAD advice here as well (as your post so blessfully proves), and I was rapt with false bravado after I first posted about running my I/C'd Z at 15psi and the reply said "hey, you're good on stock fuel management for up to about 250BHP"....I'm not going to name that poster (as a recent post requested, in opposition)...so, gee, I guess that means I was too stupid to disbelieve it then, and too ill-informed to do anything but accept that someone says that advice was wrong NOW, eh?!!?

I am not saying you're without merit that some of my replies were terse, but I detect your monkey wrench of arrogance you went to great lengths to throw at me only shows a type of smug technical one upmanship that I hoped was the minority on this list.

Obviously, you're the type who'd say "just stay stock" to everyone using less than your level headed inquiry method who might have a dead car, or one just short of blowing up, from ricers to fuzzy dicers..b/c, yes, I don't give a flying arse about getting hours "doing work on my car" which puts me in a "pay others, but know what's wrong beforehand, if possible" and would like to feel that their recommended combination of products are SAFE, AND EFFECTIVE WHEN USED AS DIRECTED (as is so often portrayed in aftermarket sales aura as to be "plug and play", at least with a near bulletproof car as the Japanese made in most Z models).

It is sad that you are so arrogant, like a mediocre guitar teacher with a 59 Les Paul Custom telling his student, say a young prodigy on a Harmony "Gibson", that "unless he studies music theory, intonation, tableture and other "lively arts" (of the dispossesed administration), then he'll never get to play to sellout crowds, or maybe play anywhere.

Frankly your bad spiritedness might come in your neck of the woods from arrogant fatheads like Jerry Garcia (to say nothing of your Silicon cowpokes), the former known as a technical master and fussy bastard with his custom Alembic guitars, and anyone not on his level was pushed aside but THIS LIST doesn't have a level of relative experience rating scale (thankfully), so that "technical" artists of Z's might willing to SHARE and BORROW ideas and experience without bad mouthing the less technically inclined.

Whatever...this list isn't likely to be an "owners manual" for my car, no matter how clearly I have attempted to describe the issues with it. Your reply is probably as useful as listening to Bob and Ray laughing on Car Talk on NPR...all the same, it is a pity that one asks for help and gets stood on with so-called expert power.

Wow, what a rant of "spoon fed" nonsense...how bout' switching Z's!!? There's not a problem folks out west couldn't fix, eh? Anyone want to trade? The reality is, as far as I've searched here, there's no one recipe for fuel management brands sizes (as in a quantifiable parts list, etc)...just look at the so-called "injector upgrade list" in Announcements. Maybe one size really doesn't fit all (just as there are very few options off the shelf for a simple 3" exhaust for my 280ZXT). It's good these tweaks are one size doesn't fit all, and SOME people are listening to my frustrated issue/rant...maybe not, b/c apparently,...oh sheesh, what a waste of time, p.o anyways!

John-my real name

[Afshin]

WOW! mother of all rambles

Well time being valuable I only read the first few sentences and the last few. As I said, the reason for the post related to your ATTITUDE in your responses to people who posted in the spirit of helping you, not your lack of knowledge (you criticized people using standard basic automotive terminology instead of asking politely or reading or doing a proper search), obviously you do not get it. However, I will admit, you are consistent, still have no idea what you are talking about, my real name is Afshin (hint, there are other languages asides from English).

[COZY Z COLE]

Whew...... It must be the Holiday Season, usually the way this thread has turned out would of had me upset, but I found myself laughing out loud at it.

 

 

 

LARRY

[Guest bastaad525]

Hey... is this guy trying to challenge me for "longest post" rites? OH NO HE DIDN'T!

 

 

First off, there IS no debate in the merits of cleaning off the connections... How do you 'debate' something that is a known fact that it has worked for so many of the members here, including myself?

 

MANY of us here have had the EXACT same problems you are describing ,with the bucking and stumbling and often backfiring, and not always only on boost... hell not even always only on turbo charged Z's! Then we have cleaned off all of the wiring harness connections as I suggested and the problem VANISHED, just like that. If you want to spend hundreds on a new AFM without just trying something that is not only cheap, at about $10 total, and easy, taking only 20 mins or so of your time... well then, more power to you I suppose. But fact is that this solution is often the only solution you would need and buying a new AFM may be a LARGE waste of money. We wouldn't recommend it to you if it hasn't worked for us. I mean just about anyone can do this easily, the only tool you even need would be a small screwdriver with which to remove the little metal clips from the connectors... And yet you were not even willing to consider it.

 

 

And I did point out a place to buy an adjustable FPR in your post on one of the other sections of the forum, I gave a link directly to the ordering page of the MSD adj. FPR costing about $60. However there would be no point to upgrading this part at this time, as it will not solve your problem, UNLESS you know for certain your stock one is bad. But fact is you didn't even check back there to see that I had given you the info you requested.

 

 

And no, whomever told you the stock EFI was good to 250bhp was not that far off. At 15psi you would be well past this amount of power. Garrett76zt, a member of this forum, is running 15psi on what is still really a mild setup (still stock turbo and EFI with a few upgrades such as bigger injectors), and is making 276hp to the rear wheels, or about 325bhp! Yes he's not stock but the point is that that's about how much power 15psi is good for out of the stock T3. At 10psi I made 200rwhp, or roughly 240bhp, on 100% stock everything with no intercooler, and only running a little bit lean on the very top end of the RPM. So no the advice wasn't "bad" at all.

 

 

I agree with Afshin's sentiment... I feel like, after taking MY time to help you, not only did you not even say thanks, you instead turn around and throw it at me like "thanks for nothing". I can't begrudge you for not being that knowledgeable about cars... hell we all had to start learning somewhere, no one is born car smart, but I will say this is NOT the place to start your education. That's like a gradeschooler showing up at the local college one day and wondering why none of what your professors are saying to you is making any sense.

 

 

If you don't already have one I strongly suggest you pick up a Haynes manual from just about any common auto parts store... just about everything you need to know is in there, from changing and gapping spark plugs, to how to rebuild your motor from the ground up, would be covered in that book. ANYONE who owns and drives anything other than a brand-spanking-new car would benefit from owning one of these books. With it, you would be much better equipped to deal with the problems your car throws your way (or at least understand them better so the sheisty shop mechanics wont be able to rip you off), and to trade information on forums such as this. All the 'lingo' you need to know is in there.

 

 

Well good day and good luck to you sir.

[jgkurz]

Hey bastaad525, I was wondering when you'd chime in and show everyone what a real post looks like...

[cygnusx1]

jjohart, they are only trying to help you..and doing a good job at that. I second, or third, the electrical connectors as a culprit. Also, half an hour hot-park is the perfect situation for vapor lock. Try leaving the hood open next time its parked for half an hour to see if it helps. Good luck with the car let us know when you find out what is causing the problems.

[evildky]

I had the same kind of problem with att the usual suggestion coming from the baord that your seeing here, it sounds like a fuel issue, mine was my pump failing intermitantly,which no-one suggested I guess it's a bit unusual, replaced the pump and the problem went away, and we've all been there in one form or another, I understand your frustrated but we're only trying to help so be gentle

[Guest squarefoot]

"not to mention taking a name which has no entmological entry in the English language (I searched Oxford), "....?????????

 

 

entomological-regarding the study of insects

 

etymological-regarding the history of language.

 

Apparently you did not search Oxford enough.

[Bernardd]

jjohart, you can change out your stock efi to a z31 setup by following the sticky in the turbo forum. I find/see z31 ecu's for 20-50 dollars, mafs for the same and then you'll need to source a crank angle sensor or distributor from any z31 or 85-88 Maxima. A maf from a 85-88 maxima will work as well. It's no where near 3 grand. JWT isn't anywhere near 3 grand either.

[Guest bastaad525]

Bernardd - are you saying there's a way to run the Z31 setup with the '81 280zxt 'blank' distributor, by using a Maxima CAS?