woah4 Posted December 31, 2013 Report Share Posted December 31, 2013 Hey everyone, on my 96 855 I am having an issue with a low vacuum reading, only -7psi at idle and -10psi on slowing with foot off gas from speed. Car has good even compression, makes good boost, and feels good.. But is REALLY gutless until 3500rpm... I mean I understand turbo lag, but this thing goes NOWHERE In a hurry out of boost. So here's my question, car is well maintained and stg. 0, I suppose at this point you could call it a stg. 3 performance wise... Anyhow every vacuum line has been replaced and all new silicone, new pcv etc., my afrs seem within limits I would expect, but I have never played with cam timing and I wonder if perhaps this could be my issue? I realize I can use it to shift the powerband, but since the powerband seems so far off is it possible that there may be too much overlap or something which could lower vacuum pressure? I ordered the ipd cam timing tool and want to try it, I just want to get some opinions here first. I've never driven another t5 even half as laggy as this, and I would have thought -10psi at idle to be more appropriate.. Any input is appreciated. Cheers, Billy Link to comment Share on other sites More sharing options...
Dick Dastardly Posted December 31, 2013 Report Share Posted December 31, 2013 Look at vac tree, all the caps and look for cracks also make sure the 10mm (or is it 12?) nut is tight. Make sure the PVC bracket isn't between manifold and head. Check every vac line again including the brake booster lines and check valves.Make sure vac lines are properly routed as well.. And that your evap line to intake manifold is on and sealed. Link to comment Share on other sites More sharing options...
woah4 Posted December 31, 2013 Author Report Share Posted December 31, 2013 Yeah what I've done so far... All vac lines, put a cap over the spot on the mani for evap, all caps on tree are good and i tried spraying the tree with brake clean with the engine running without change, so I assume it is sealing... The only vac line I didn't change was brake booster but I removed the booster line today and capped it, started the car and vacuum read the same as with it hooked up, so I can only assume it is ok, not sure what you mean by PVC bracket? I'll go over it again tommarow, thanks Billy Link to comment Share on other sites More sharing options...
hotpantslovebug Posted December 31, 2013 Report Share Posted December 31, 2013 Is your idle high? Do you know your LTFT value? almost went crazy tracking my vacuum leak down, propane nor carb cleaner didn't find it. Since your vacuum is so low I'm guessing you have a large vacuum leak. can you hear any hissing in the engine bay? You'll want to check around the PTC aswell. all else fails you can always make a homemade smoke tester. Link to comment Share on other sites More sharing options...
gdog Posted December 31, 2013 Report Share Posted December 31, 2013 Yep, either large vacuum leak or running too much overlap on cam timing; are you running N/A cams by chance? Also ck vac line on left side (passenger side of car in usa) of intake manifold that goes to PCV; pull off line and cap manifold fitting. If you get better vac at idle, then that plastic line is likely broken. Link to comment Share on other sites More sharing options...
woah4 Posted December 31, 2013 Author Report Share Posted December 31, 2013 I'll have another look tommarow. No noises that stand out to me in the engine bay... The only thing is I seem to get a lot of valve noise, like lifter tick, my other 850's were noticably quiter than this car. I'll see about making a smoke tester, I know it will run way better once I get this sorted... It just been driving me bonkers lol. Idle is normal, no codes either.. It's m4.4 tuned. Ltft seems normal to me. Again everything seems ok... But my gauges tell me otherwise, and how sluggish the car feels does too... Cheers, BillyAnd sorry no to NA cams. I have not pulled the cam cover off yet even on this engine, however the timing belt was done not long before I got the car, and I am not sure of how maintenance was kept up prior to my ownership so who knows where the cam timing could be at... That's why if it seems plausible I think there is a real chance that could be it, just not sure if anyone has experienced symptoms similar to this before. Until my tool arrives I'll keep searching for vacuum leaks... Link to comment Share on other sites More sharing options...
Horses With Gas Posted December 31, 2013 Report Share Posted December 31, 2013 woah4, Assuming the system holds appropriate pressure/vac, Camshaft overlap could be the problem. On my lpt wagon, I was seeing vacuum readings of about 15-16mmHg (in drive) and 19mmHg (in Park). Off-the-line acceleration was lazy. In an attempt to minimize any cam overlap, I used an IPD cam timing adjustment tool. The initial values I saw were approximately Intake:+2 Exhaust -2. After some adjustment, I settled on these new values - problem solved. Intake:-2, Exhaust +2 i.e. 4 degrees of separation. I first set the intake cam for a base of where I wanted the power to be emphasized in the rpm-band, then set the exhaust cam to dial out overlap. I suspect that 2-degrees of separation is sufficient to minimize the effect of overlap for these stock cams. The new vacuum readings (vehicle fully warmed up) are at 18 (Drive) and 21 (Park). Link to comment Share on other sites More sharing options...
woah4 Posted December 31, 2013 Author Report Share Posted December 31, 2013 Ok great that's what I was hoping to hear. And it got rid of the low end lazy ness? Any loss on the top end? Thanks! Billy Link to comment Share on other sites More sharing options...
Horses With Gas Posted December 31, 2013 Report Share Posted December 31, 2013 The low-end responsiveness improved. The overall performance now seems to be well balanced, with no loss on top end. Initially, higher rpms were favored. When I was making the adjustments I had this in mind...balanced powerband with improved low-end response and minimal overlap. Even a 1 degree adjustment can make a significant change in the vac readings and powerband behavior. I found that keeping the intake cam close to zero, but advancing the exhaust cam to reduce overlap kept power delivery balanced. I noted that I:0 E:+2 has similar performance as I:-2 E:+2 with vacuum readings at 17+ (drive) 20+(park), but I:0 E:+2 seems to have more low-rpm performance (slightly faster to 60mph). The info at this link might be useful. '?do=embed' frameborder='0' data-embedContent>> Link to comment Share on other sites More sharing options...
Rod'sT-5 Posted January 1, 2014 Report Share Posted January 1, 2014 Woah4, why dont you post up a datalog of a long drive, so we can look for possible issues. Link to comment Share on other sites More sharing options...
woah4 Posted January 1, 2014 Author Report Share Posted January 1, 2014 Alright I'll see what I can do, I am not logging afrs or boost pressure yet but I guess what you really want to see if timing pull and ltft anyway. I should be doing some running around tommarow so I will try and get a log. Also thanks for the link horses with gas, I am definently going to be curious to see where my cams are at... Something has just seemed off on this car since I got it. Cheers guys and happy New Years, Billy Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.