| I've done many a search on this issue (for weeks now). I run into a lot of posts and response situations, but very few have come back to report what the problem was. Thus far, none of the reported solutions are my problem. Hopefully you will see from the novel written below that I am not wasting your time posting an issue that I haven't fully looked into. I'm trying to figure out why I'm having a loss of power at high RPM. The car seems to run normally up until around 4500 rpm, then the power just levels off. I guess you could call this hesitation, but there is no stumble or apparent misfire. The car runs like a champ, 100% great, except for this. I have studied the hestitation FAQ thoroughly. This problem has gradually become worse. I noticed it the first time I visited the strip (wasn't able to pull to hard 7K - really the first time I'd ever tried). Pulling to 6500 was fine, and I wasn't too worried about my times (first visit) but my MPH was at 100, no better (should be better with my mods). Ever since, I've been trying to figure it out, and with everything I do, I go out to test and nothing has changed. Over time, it just gets worse. Now, as said, 4500 is where things level off. Right now my direction of thought is that there is something wrong with the electrical system, spark blow out, or something else like this making the car run too rich. I have not monitored my fuel mileage lately...my wife told me she saw a limited amount of smoke come out of the pipes when she was following behind me one day. I have never seen smoke from the driver seat, however. As my car is not powering well, I have not taken it in for a DYNO as I feel it would be a waste of money...however, it might be nice to know how rich she is right now. BOOST hits peak and holds (whether set at 10, 11, 15, you name it), but the car is just sluggish. I don't think I could pull to redline in any gear other than maybe 1st or 2nd. Boost picks up quickly (no real lag compared to any other time I've owned the car). The injectors check out good from ECU to Injector (ohms exactly the same on each at 12.4), so the wires are good and the injectors have the proper reading. I replaced one injector at the beginning of this year because it was reading 40 ohm (didn't make a performance difference when replaced - I was troubleshooting detonation at the time, which turned out to be bad fuel from several different stations - I have not heard detonation since!). I replaced another injector about two months ago because it completely died (lost a cylinder coming home)...it was OL on my FLUKE. Once replaced, back to normal. The fuel pressure is good (43.5 at zero, 60 maybe 61 at WOT). Reads only 1 psi low sometimes when HOLDING 5 psi boost (reads maybe 48). I changed the fuel filter yesterday and have only a placebo feel change in performance. I replaced the FPR, DAMPER and associated fuel hose when it was getting cold last year. The FPR I have checked many times for proper operation, and it's fine. I smell no fuel and have no detected leaks...fuel pressure stays up in system for start up, etc...it's not bleeding off. I checked all the coil packs and the ohms are good. Also recently replaced all the coil pack connectors. The fuel pump resistance is right on -- I've never had a problem with start up. I checked all my plugs and they are gapped properly (.035), they are the cold plugs, and the condition looks NORMAL according to the plug condition charts, etc, that I've studied. I wonder if the plugs have just slowly degraded, but the plugs are only about 10K old (if that, probably less). More on this below (talking about electrical system). I do not detect detonation. My timing is at 15 BTDC. Car idles perfectly and fires great. It seems to fire just fine at the upper RPM, but just doesn't go anywhere (feels like a rev limiter/retard feel). I don't think there is anything wrong with the compression, but I do still need to check it. This upper RPM thing has been slowly getting worse. I'm starting to think it may be an electrical problem (ie, battery/alternator). I recently replaced my main battery cable with OEM and it didn't make a lick of difference (the old battery clamps were BARELY hanging on). I also wonder if the plugs have just slowly degraded, but the plugs are only about 10K old (if that, probably less). I have checked for boost leaks a million times. I found several and fixed them. Once I had a problem with ZERO boost, but found the compressor outlet hoses were loose, tightened them down, and had boost back. I still have one back on the EGR (from below - the valve is still operational and the diaphragm hold vacuum) and I believe a new one on the exhaust or cam cover gasket. However, I understand that neither of these should affect performance as I am experiencing (though the cam leak should be sealed). In fact, the EGR leak has been there throughout the degredation, so it seems not to be a factor (plus, I'm still holding whatever boost I'm set at)...car just isn't going anywhere. To add to the confusion, it would seem that if I'm just cruising for a while without punching it, I can get a good punch through one maybe two gears, then the high end dies down again. I'm almost thinking electrical components are heating up and then the system is not able to stay up with the load. I recently relocated the PTU (yesterday) and that didn't make any difference. All the contacts were shiny and new looking...no corrosion at all. I did still put some dielectric grease on the connections to be safe down the road. The PTU is the updated (black box) model, though when I called NISSAN they said there was never a recall for my car nor was a recall ever performed (which seems a bit weird since I have a 91 TT). I replaced my fuel temp sensor, CHTS, and coolant temp sensors and that didn't make a lick of difference. I get ZERO codes when doing ECU diags...I never have had codes. I checked O2 operation and it's good. The car has only 82K on it - 67K when I purchased it over two years ago. I have removed AIV and PRVR systems -- also didn't make any difference. I've never had a problem with emissions tests. I recently installed cat-pipes and it seemed to allow a bit more breathing in the upper range, but still didn't solve the problem anything significant. I have downpipes and catback also installed. I've checked the TPS to see if continuity changes with throttle - responds as it should. The contacts there are good, too. Throttle bodies are clean (no excessive deposits past the valves). Air filter (JWT Pop) has about 8K on it...it's a bit dirty, but I don't think it's the issue....they say you can go forever with them. I'd hate myself if after everything if it turns out to be the filter, so I am going to clean it soon (certainly would be a GRADUAL problem). I have not done the DUCT TAPE thing because I've had the filter set up this way from the beginning and I used to have better upper end power....don't think that is an issue (although it's also something simple maybe I should try just for kicks). I have not done TESTS on the MAF...it does not show up on codes, but who knows, maybe???? I do get a very occasional, small backfire sound (not the loud kind that causes accidents : ), when letting off throttle. In fact, I've only ever heard it when reving at a stand still (checking for an exhaust leak) -- never have heard it in normal driving. So, all said, I'm truly at a loss. I was very discouraged to fine a new leak on that seal at the back of the engine. Just added injury to insult. There has always been a bit of oil back there (was advised when I first bought the car). It is nothing "gushing", just that dirty, caked on stuff. Now there is a steady hiss back there when doing a leak test. Let me know your ideas....and I WILL POST A VERY DEFINITIVE follow-up if I ever figure this out!!!!! I hope to be able to pinpoint the problem instead of just doing a million things and having it magically disappear without a clear reason as to why. I hope I have not left anything out -- if I have, please ask and I will answer. -Dave
Z's Rule! |
