Hello Everyone,

I get 8-9 inches of Vaccum on a 93 T/A with all the goodies, ported heads, and an XE 230/236 cam w/ an LSA of 112.

Symtoms:
-Idle is Rough, it tries to die at times and the ECM tries to adjust. I am not saying Cam lope is crazy, just that idles goes up and down. But most of the time it stays at 850 rpms or so.

-Down in power (best E.T was a 13.9 at 102mph )

-Seems to runs rich (Very rich)

I have replace with new parts:
1 Replaced Opti and its harness, coil, wires, and plugs.

2 Converted to heated 0'2 sensors (now goes into closed loop in seconds)

3 I have no external vaccum leaks, fuel pressure regular is new (hypertech adjustable). Fuel pressure is 43 psi and remains there.

4. I have adjusted the rockers and checked valve lash - no problems.

My question is what are the possible causes of such low vaccumm. Is it tuning (I have PCM4less tuning) or is it mechanical.

Other than idle, the car feels fine...no missing, hardly any hesitation, no bucks, no surging. Just a complete lack of power, richness, occasional stalling, and a low vaccumm reading.

Someone suggested to check my timing chaing alingment (dot to dot) but I do not think it is that. It was built by an experienced engine builder. He says it might be on tooth off - which makes sense.

But if it was that, would the car ever run, accelarate normally, and such?

Thanks, I am desperate and I am running out of patience and time (I go back to shchool on the 25th).

 

TTT,

Please, anyone with this experience?

 

my guess would be a vacuum leak is to blame...


but heres a ttt for ya

 

FWIW, also be careful where you measure the vacuum if you are teeing into some stock manifold fittings. I saw more than a few inches difference just based on where I measured it. You might want to take a reading in a slightly different location (or maybe you have a perfect connect already, I dunno).

 

I am grabbing my reading from opti vaccum port....on the driver side of the engine....

I know it is accurate, because my map readings confirm this.


Vaccum = Bar (20.xx) - Map (ranges between 20.xx to 21.xx) = 10 to 9 inches.

Any ideas?

 

Tough issue, can only think of more tests to do. Try measuring the vacuum again but this time use clamps to pinch off the other vacuum lines as you are monitoring the vacuum level. Do it one at a time until you see if the vac level rises. I use needle nose vise grips with fuel line over the jaws so as to not damage the lines.

You could pull one off at a time and plug the port and the hose by hand and check the reading. This would work if only one is the bad guy. If more than one is the problem, you would need more hands obviously.

If that doesn't find the problem, the only other thing I can think of to check is start from the basics and do a leak down test. This can give you the answer to whether you have the valve timing correct or not as well as other possible causes.

 

What lifter preload are you using? Maybe too tight?

 

Seems like Im not the only one having cam problems. Close to the same symptoms too.

Unstable idle, loss in power, starting problems, wont hardly idle with AC on, some surge, but mine is missing!

 

Rough idle can be the IAC, I took my old one apart and Oh my god.

 

Since you can read your MAP sensor, look at the IAC volts and see if they are jumping around. That could be the culprit.

 

what's an IAC?

i'm having very similar problems. sometimes,when i shift from park to D, it stalls.
mods on sig.

i'm gonna take it to another shop on monday to get it dynoed and get them to check the vacuum. this new motor is giving me LOTS of trouble.

please, keep us updated.

 

Idle air control valve, its the electrical doo-hickey on the underside of your throttle body. It is what controls the air comming in at idle when the TB blades are closed.

 

You should be taking your vacuum reading straight off the vacuum port on the side of your intake manifold above the PCV valve. You should also be getting a steady vacuum of between 17 and 22 inches. I'd do a compression test and a leak down test as well.