ZCar Forum banner

vacuum readings

476 Views 9 Replies 4 Participants Last post by  steves280
just checked vacuum levels off the line that runs to my boost guage sending unit.. i found about 5psi while (attempted) idle. seems like i have a leak somewhere.

anyone know if this page 'tech tips' applies to all of the L series engines?

just want to be certain there's a problem...


Post Edited (Oct 6, 7:03pm)
Not open for further replies.
1 - 10 of 10 Posts
maybe im not reading that right.. later on it says 5psi is normal at idle..
i think the first readings are when you rev it up.. mine gets up there.
Vacuum changes with the fuel mixture so using it to confirm a leak is a joke.

You need to open up the AFM and see if moving the arm one way or the other will help it try to idle. But first have you unplugged and plugged back in the ECU? Seem this fix lots of weird problems with ZXT's.
i've had the ecu connectors off and on several times to do the sensor checks so it's safe to rule that out as a solution.

i just did some testing and found that i get better vacuum to the AAC via a new hose than through the steel pipes running along side of the intake manifold.

i checked out the plugs earlier and they confirmed i am running rich. they were a little wet with gas around the threads towards the tip. they were all the same which rules out individual cylinders causing the problem.

my afm has only been opened once because i thought the air temp sensor was bad. turns out my multimeter was just on the wrong setting so i sealed it back up. it ohms out correctly during the sweep and for the limits. i really dont think anythings wrong with it.

im currently looking in the fsm for procedure for checking/setting the timing.. i know it was set right with everything hooked up but i could swear you have to unhook the tps and maybe something else..
Yes you need to unplug your TPS, I tried to set mine going by the book, 20 degs?, but finally just set it by ear, havent had to touch it for months , runs better then new, well I guess, I didnt have it new, if I had it would not be in the shape its being pulled out of now. My Idle is set around 950 rpms, a little high but makes alot of difference, At idle it sounds perfect.

Im running right at 19 on the vacuum at Idle.

When I replaced my ACC I got one with a adjustment screw, You can really fine tune the Idle, Heck I leave the stupid allen wrench in the ACC, so I can play any time I want, and You know how us Zers love to TWEAK!!!

The vacuum gauge test is reliable for about 95% of engines running WORLDWIDE,
not just L series.

But, it is primarily used to diagnose a - running - engine, and very effective in finding a - mechanical - problem as described in the tips.

5 INCHES (not psi) is normal at CRANKING, not at idle. At idle, a decent engine averages about 19 inches hg, and fluctuations in the gauge can point you in the best direction for mechanical issues.

It cannot, however, diagnose cranking problems, no-start problems, fuel issues, (delivery, pressure, etc.) find leaks, as Steves280 pointed out, so you need to go the "No Start" troubleshooting arena.

Spark - Fuel - Air ! ! !
For anyone questioning if fuel mixture affects vacuum readings: take the lid off the AFM, connect a vacuum gauge and at idle move the AFM wiper while watching the vac gauge.

Assuming that you have a leak because the vac is low is WRONG.
checked timing tonight. i disconnected the tps. at 'attempted' idle, it's advanced a bit, probably about 12-15 degrees. when i get the rpms up there, it tops out at 24 degrees.. seems like it's doing what it's supposed to there.

i tried disconnecting the larger diameter hose (one going to top of intake manifold over to canister on driver's side lower plug) and it didn't make the car run better.

i think my plugs may be fouled enough now that im not going to see improvement of any sort until i clean them. also, after the last time i changed the plugs it ran almost perfect for a few days. now it's running worse than when i posted my first post here earlier this week, even above 2500. it still runs noticably better once it gets over 2500 though.

know of somewhere that someone has afm adjustments for an 83zxt afm? i dont really like the idea of messing with it but i'm running out of ideas.
The other very likely posibility from my experience is a flaked out ECU. Replaced lots and lots of them for weird running problems like this..
1 - 10 of 10 Posts
Not open for further replies.