ID'ing a bad Supercharger?

It's quite possible for the dealers techs to not find any number of problems, many (certainly not all) are not particularly good these days.

First and foremost contact the manufacturer directly and be prepared to give them the details of the various visits for service. They may have better information in their database or information that the dealer's techs missed. They may also be able to provide other assistance in resolving the problem.

An engine with a supercharger can be pretty complex, particularly the controls for it. There are any number of problems that could cause it to malfunction, particularly bad sensors that may not have fully failed enough to flag a fault and would only be found by someone who knows what they are doing looking at recorded scan data from a test drive.

Good luck.

Pete C.

A supercharger is nothing more than a gear or two in a housing. If the drive belt has come off of the SC pulley then the SC is not working. Its that simple. The problem you are experiencing is likely due to a sensor malfunction, O2, MAF, TPS, temp, knock, etc. There are tens of them. If you use regular gas the engine will retard timing leading to lack of power. Etc.

do you have a boost gauge, or the ability to install one yourself? this will tell you if you've got a blower problem or not, and if you take it back to the dealer and say "I have no boost" as opposed to "the engine feels down on power" they will probably take you more seriously.

good luck,

nate

I'm not a mechanic at all but I know someone who is and has a boost gauge. I've spoken with him and he's going to check out the boost next week. If there's anything interesting to report, I'll post it here. Thanks to everyone who responded. :)

I'll second that...first thought was a defective knock sensor making it command ignition retard under boost...something like that...On the semi's I drive, they'll loose power sometimes and I'll find it partly blew a duct off the turbo routing...that wouldn't be the case here, unless you are intercooled, then it coulda popped one partially off the intercooler and is blowing your boost out in the open...

The SC drive belt is fine. I've owned the vehicle since it was new and I've always used Supreme gasoline. Thanks for your comments.

A SC compresses the air that is fed into it. If the engine lacks power then I would suspect it is not getting enough fuel or restricted exhaust. Check the MAF. If the exhaust is clogged, then the O2 sensors are shot as well.

All it takes is a manifold pressure gauge to see if its producing the boost it should produce.

Update --- It seems like "jeffcoslacker" may be right:

This morning my mechanic friend checked out the boost pressure on my Xterra SE S/C as suggested by some replies to my OP. The maximum boost pressure was 2 psi, which he felt was rather low. He tried to get the pressure spec from the Nissan dealer but they wouldn't give it to him. He also checked the codes and found a "DTC P0328: Knock Sensor Circuit High Input" (Mitchell codes). He reset it twice and after each additional test drive the code was there again. Armed with this new information, I've made another appointment with the Nissan dealer for tomorrow. I have no idea why they would not have found a code when I've had the vehicle there previously for this loss of power problem. The very first time I took it in for this loss of power problem, they actually replaced the manifold gaskets under warranty (gave us a loaner car and all) but that never made any difference to the loss of power problem. Based on today's findings and the Nissian dealer's instance on recent occasions that the vehicle is operating just fine, does anyone have any suggestions as to how to handle things with the Nissan service department tomorrow?

2 PSI is worthless; if that were the pressure the blower were designed to put out, it wouldn't be worth the trouble to bolt it on the engine. now the question is, is the blower bad or is the boost pressure being regulated low because of the knock sensor? I can't answer these questions but maybe the dealer can; I'd just tell him what you just told us and state that you don't know what the max. boost spec is but you know that it has to be higher than 2 PSI (because it does. Even a "light pressure" blower puts out somewhere between 5 and 7 psi.)

nate

As others have stated, low boost pressure would cause weak performance and possibly not set a code if it was a minimal loss in pressure. But it's most likely that your supercharger is still OK as the only "wear items" in the housing are the shaft bearings and scissor gears (or whatever timing mechanism your SC uses). IOW, you would hear something awry if a mechanical failure occured in the SC.

With your new info regarding the knock sensor code and the 2 psi manifold pressure reading, it all seems to make sense. The knock sensor is failing and reporting too much noise, therefore commanding the SC bypass valve to open and redirect boosted air into the upper plenum. I'm sure timing is retarded and fuel control is modified as well, but your Xterra also has the boost bypass valve, hence 2 psi of pressure. It's also possible that you didn't check the intake pressure under load at high RPM. Since the ECM can control boost, it likely does so all of the time to minimize boost when not needed. Two psi manifold pressure under no load sounds feasible to compensate for the lower static compression I assume that your engine has.

Toyota MDT in MO

"Comboverfish" wrote:

Update No. 2 --- I had my Xterra to the Nissan dealer today for the loss of power problem (discussed earlier in this thread.) I gave them the Mitchell Code sheets for the knock sensor problem, explained the super charger pressure test results and the loss of power when driving. They asked me "How long has the engine light been on?" I told them it has never been on. They then asked why I had taken the Xterra to a garage to have the super charger and codes checked if the engine light wasn't on. I explained that I know just from driving the vehicle that it does not have the power it should have. I also explained that I'd taken a trip this past Sunday and encountered a couple of big hills that made me down- shift. After that, I decided to try and get to the bottom of this long-standing problem by having another mechanic check it out. I did NOT tell them I'd also sought help on the Internet! :) The Nissan people were nice about it and took the car in for a check- up. I picked it up this afternoon. They said that they have ordered a new knock sensor and a new intake manifold gasket. According to them, a bad intake manifold has caused the knock sensor to fail. I pointed out to them that they had replaced the intake manifold gaskets during one of the previous service visits when I had taken the Xterra to them with the loss of power complaint. I asked them to check the date of that repair. They said it was February 2006. The service desk could not tell me if one or both intake manifolds were worked on at that time. Neither could the service desk tell me which gasket was going to be replaced this time. I'm now driving the vehicle while waiting for the parts to arrive. They say it will be about a week.

I'm not a mechanic but this all seems very odd to me. The loss of power problem has been ongoing for a couple of years. Nissan has checked it several times without success. Then in February they replace the manifold gasket(s) to fix the problem. The problem is still there after that repair but they say the power is fine. Now they are blaming the failure of the knock sensor on a bad manifold gasket. Does this all make sense?

I suppose that it is possible, but really, in a word, no. I just don't see what connection there would be between intake gaskets and a knock sensor, unless an intake gasket were causing a lean condition (in which case the knock sensor would activate, but correctly so, and there would be no need to replace it, and the MIL would also be on.)

nate

If I'm not mistaken, the knock sensor (I think there's only one on the

3.3) is in the intake valley underneath the intake manifold. At this point the intake will have to come off again to replace the sensor so your concerns are basically moot. Perhaps there was a bulletin that detailed replacing the intake gaskets for your original complaint the first time in. Perhaps the mechanic threw them on without diagnosing anything. I don't believe that gasket failure could cause a false knock input to the ECM, but stranger things have happened. Sounds like BS to me. Hopefully the KS will fix your power issue.

A KS problem turns on the SES after one occurance (one trip logic), but you are experiencing the code in memory without ever seeing the SES come on. This seems odd. Perhaps the intake gasket job was botched and there is a pressure leak under boost. This may not be detected by the ECM based on how sensitive their programming is to MAF sensor changes. There's no MAP sensor AFAIR so there's no direct intake pressure input with which to make a diagnostic decision. But under full power the ECM wouldn't set other related codes like too rich or too lean, so this may be your problem. The one thing that sticks in my head as to why a bad gasket would cause false knock info is if a blast of air pressure were to hit the sensor directly and set it off. Still unlikely....

Toyota MDT in MO

Reply to my last comment:

I just logged on to my work's service info service and looked at SES strategy for the Xterra 3.3 KS circuit. A failure will not turn on the SES. I know the cars I've diagnosed with KS codes have lit the SES, so that's a new one on me. So maybe the KS is sending crap info all of the time and the POS ECM strategy is such that it doesn't care if you know. How odd....

Toyota MDT in MO

Its also possible that the engine has other internal noises that are fooling the knock sensor. Wrist pin noise is often a cause for false knock detections.

It does if you're a dealer service department trying to CYA... :-/

I also havea 2002 xterra with s/c and I am experiencing the exact same problem. Just last night I read the codes from the x and got p0328. bad knock sensor. I also got codes p0420 and p0430. these indicate catalyst above threshold at banks 1 and 2. after reseaech this basically states that my catalytic conv. are not doing there job, I have an exhaust leak, or I need new conv. does this sound about right? I really dont have the time or money to fool around and try to find the problem so I am hoping you can keep me updated on your situation and help me solve my problem.

XJ

The only code found when I had my vehicle checked recently was the P0328. On a previous occasion when I had my Xterra in for this on- going loss of power problem, there were other codes present. The garage cleared them and apparently they never came back, so I don't even know what they were. I'm still awaiting the arrival of the parts for my repair. I will post the results back to this thread once the repairs are done.