peeeot Posted October 21, 2006 Report Share Posted October 21, 2006 What should the manifold vacuum be for a 3.1 in park? Quote Link to comment Share on other sites More sharing options...
19Cutlass94 Posted October 21, 2006 Report Share Posted October 21, 2006 Correct me if Im wrong but I believe its somewhere around 23 inches of vaccum. ( if Im remembering the right number ) Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 25, 2006 Author Report Share Posted October 25, 2006 where did you take that reading? Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 28, 2006 Author Report Share Posted October 28, 2006 I just retook manifold vacuum. at idle in park at 1000 rpm, the reading was just shy of 19; when it wramed up a bit more and slowed to about 800 rpm, the reading dropped to a mere 15-16. These readings were taken at the vacuum modulator port right beside the throttle body. Too low!! Quote Link to comment Share on other sites More sharing options...
z284pwr Posted October 28, 2006 Report Share Posted October 28, 2006 I know mine doesn't count, but mine is ~11 on a good day... Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 28, 2006 Author Report Share Posted October 28, 2006 why doesn't yours count? Makes mine look like a champ.... Quote Link to comment Share on other sites More sharing options...
GutlessSupreme Posted October 28, 2006 Report Share Posted October 28, 2006 I just retook manifold vacuum. at idle in park at 1000 rpm, the reading was just shy of 19; when it wramed up a bit more and slowed to about 800 rpm, the reading dropped to a mere 15-16. These readings were taken at the vacuum modulator port right beside the throttle body. Too low!! hum.. time for a compression check! could be a bad gasket somewhere but that's usually more noticable.. Quote Link to comment Share on other sites More sharing options...
19Cutlass94 Posted October 28, 2006 Report Share Posted October 28, 2006 More than likely, you would notice a bad gasket. It could be the rings giving you this, could be a burnt valve.... Theres alot of things that can cause you to loose compression. Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 28, 2006 Author Report Share Posted October 28, 2006 I don't like where this is going.... When I bought the car the previous owner said that the head gaskets had been replaced. I don't know how long ago that was (that they were replaced), but I thought it strange since the car only had 84,500 miles. I had been driving it for quite a while (since buying it) before I discovered that the vacuum line connected to the vacuum tank was broken/disconnected. It ran better after fixing that, but I've taken vacuum readings with it connected and with it disconnected and that leakage hardly affects the manifold vac at all. Maybe by .5" Hg max. A reading taken at that line yields a steady 18 inches. I've learned that a compression test is supposed to be done with the engine warm, but since this car has aluminum heads I can't take the spark plugs out with the engine warm. How have ya'll done it? Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 28, 2006 Report Share Posted October 28, 2006 I've learned that a compression test is supposed to be done with the engine warm, but since this car has aluminum heads I can't take the spark plugs out with the engine warm. How have ya'll done it? yeah, when it's warm. don't do it when it's at operating temp. just warm, like after you let the car sit for an hour. Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 28, 2006 Report Share Posted October 28, 2006 why doesn't yours count? i think he might have an aftermarket camshaft. Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 28, 2006 Report Share Posted October 28, 2006 I just retook manifold vacuum. at idle in park at 1000 rpm, the reading was just shy of 19; when it wramed up a bit more and slowed to about 800 rpm, the reading dropped to a mere 15-16. These readings were taken at the vacuum modulator port right beside the throttle body. Too low!! those vacuum readings sound perfectly fine to me! Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 28, 2006 Report Share Posted October 28, 2006 I know mine doesn't count, but mine is ~11 on a good day... mine is around 12" and that is with the stock camshaft. i was using a mechanical Autometer boost/vac gauge which i think are complete inaccurate pieces of junk! IF my vacuum really is that low, it is likely due to worn piston rings due to my high mileage engine. the engine still runs great though to say the least. however, i have noticed NO signs of blowby so maybe something else is causing low vacuum? the engine has new head gaskets with heads that were resurfaced last year and i KNOW they don't leak. i haven't done a compression test yet though, never really had a reason to. maybe i'll do that on Monday just to see what it is. Quote Link to comment Share on other sites More sharing options...
z284pwr Posted October 29, 2006 Report Share Posted October 29, 2006 Yes, bigger cam will affect it, which I do have, plus at 4500 feet, it affects it too Cousin's 383 barely had 5.... Thats why mine doesn't count.....I have a big cam....it only got 12-14 with a 5spd and thats with a verified correct vacuum gauge....so I'm not to worried about it... Engine only has oh about 15,000 miles I believe..... Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 29, 2006 Author Report Share Posted October 29, 2006 I found an article that has a lot of interesting and useful information pertaining to vacuum and possible trouble areas. The following quote was of particular interest to me: "Low vacuum also can be an immediate clue to a plugged exhaust. To check further, run the engine at about 2500 rpm for about 15 seconds. If vacuum drops during this period and does not increase when you close the throttle, you're almost certainly looking at a restricted exhaust." I have another thread about catalytic converter replacement; that thread and this one are starting to run together a bit (sorry ) because I don't want to replace my cat until I know the engine is operating properly such that it won't mess up a new one. The old one is rattling, especially when the engine is under load. Well, that quote indicates that maybe the cat, or perhaps my rusty-looking muffler, is itself the cause of the low vacuum! I'm definitely going to do the test it describes. Much easier than a compression test, and makes more sense based on my situation. Here's the address for the rest of the article: http://www.findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956 TurboSedan: I wonder whether your low vacuum readings are a product of your turbocharger. From Wikipedia: "When the throttle is opened (in a car, the accelerator pedal is depressed), ambient air is free to fill the intake manifold, increasing the pressure (filling the vacuum). A carburetor or fuel injection system adds fuel to the airflow in the correct proportion, providing energy to the engine. When the throttle is opened all the way, the engine's air induction system is exposed to full atmospheric pressure, and maximum airflow through the engine is achieved. In a "naturally-aspirated" engine, total engine output is thus determined by the ambient barometric pressure. Superchargers and turbochargers can "boost" manifold pressure to above atmospheric pressure, usually by a maximum of 0.7 bar." I don't know whether it spins enough at idle to affect anything at all, but perhaps your turbo just slightly reduces the pressure differential between the manifold and the atmosphere, resulting in lower vacuum readings. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted October 29, 2006 Report Share Posted October 29, 2006 Josh, you and Brian need to take into account elevation when looking at your vacuum readings. The typical rule of thumb is 1 inHG lower vacuum reading per 1,000' elevation increase. Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 29, 2006 Report Share Posted October 29, 2006 Josh, you and Brian need to take into account elevation when looking at your vacuum readings. The typical rule of thumb is 1 inHG lower vacuum reading per 1,000' elevation increase. ah, good point. i never really considered that. i know elevation affects boost but i never even really thought about the vacuum aspect, which makes sense. thanks. Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 29, 2006 Author Report Share Posted October 29, 2006 I performed the test that I mentioned, and the vacuum behaved exactly as it should. Moreover, with the engine properly warmed up (6 bars), my vacuum at idle was 19 inches. Still lower than I'd expect, but maybe that's just normal for these engines. It's higher than what I'm hearing from most people. So I have no reason now to think that my engine isn't working properly, or that my exhaust is clogged. I'm actually a bit disappointed, I was hoping the exhaust was clogged so that I could find some new power by unclogging it Quote Link to comment Share on other sites More sharing options...
KCFITZ78 Posted October 30, 2006 Report Share Posted October 30, 2006 Little of subject but how do you even check vaccum pressure? Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted October 30, 2006 Report Share Posted October 30, 2006 Buy a vacuum gauge and attach it at any vacuum line. Testing is usually done at idle, after the engine is warmed up. Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 30, 2006 Report Share Posted October 30, 2006 kind of off topic, but i'm only getting ~9.5" vacuum in my GTS Turbo. it still runs great but it might be time for a rebuilt (that engine definately has some blowby). Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted October 30, 2006 Report Share Posted October 30, 2006 kind of off topic, but i'm only getting ~9.5" vacuum in my GTS Turbo. it still runs great but it might be time for a rebuilt (that engine definately has some blowby). stock cam and internals? Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 30, 2006 Report Share Posted October 30, 2006 kind of off topic, but i'm only getting ~9.5" vacuum in my GTS Turbo. it still runs great but it might be time for a rebuilt (that engine definately has some blowby). stock cam and internals? yup, all stock internals and never been rebuilt with 238,000 miles. Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 30, 2006 Author Report Share Posted October 30, 2006 Turbosedan, where are you taking that reading? There is an important distinction between ported vacuum and manifold vacuum. You have to take your reading someplace AFTER the throttle plate. As I said, I used the transmission modulator valve port, which is right after the throttle plate and facing the front of the car. If you have standard power brakes (non-ABS), the brake booster vacuum port would be the best one to use. 9.5" is definitely too low, something isn't right. When was the last time you did a tuneup? Read the article I linked to, it gives some very detailed info on troubleshooting using a vacuum gauge. Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted October 30, 2006 Report Share Posted October 30, 2006 Turbosedan, where are you taking that reading? There is an important distinction between ported vacuum and manifold vacuum. You have to take your reading someplace AFTER the throttle plate. well yeah! obviously there won't be any real vacuum before the throttle body. i'm using an Auometer mechanical vacuum/boost gauge. on my GTS, the gauge is sourced to a McMcaster-Carr manifold distribution block that is attatched directly to the intake manifold (plenum). you can see where the nylon boost/vac line runs to at the end of the distribution block here: on my Turbo Cutlass i also used the Autometer mechanical vacuum/boost gauge, but i used the port on top of the throttle body that is supposed to be used for the cruise/HVAC circiut. it was only temporarily setup that way just so i could test it (kind of ghetto): 9.5" is definitely too low, something isn't right. When was the last time you did a tuneup? the 2.2L engine in my GTS has never been rebuilt, but it has been COMPLETELY gone through in the summer of 2004. i pulled the engine out, relaced the oil pump, and replaced damn near everything. i didn't have the cylinder head rebuild or have a valvejob done either; just resurfaced. like i said though it's a high mileage engine and the rings are probably getting pretty worn. the valves could also be part of the problem. it probably doesn't help that i currently push 17psi through it. when it finally goes BOOM i'm replacing it with a BUILT 2.5L along with a bunch of other cool stuff of course Quote Link to comment Share on other sites More sharing options...
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