Got a T2 problem that's bugging the hell out of me and I thought maybe some of you guys could help me out. At stock idle I'm getting 12 " Hg which is low. I expect it to be in the 15-18" range. When I downshift the vacuum goes to 18" (I think this is a good sign).

I know engine manifold vacuum is mechanical in nature--but could a bad EGR, ACV, or check valve be the cause of my bad vacuum reading? Whatever the problem is has to be between the measurement port on the LIM and the engine--that's why I'm suspecting one of the three items above.

Engine is a stock 88 Turbo installed with stock everything into an 84 GSL-SE less the following mods:

1) No OMP, all holes and nipples bolted in and capped.
2) K+N filter
3) S5 turbo

By everything stock I mean the whole 9 yards, ECU, wiring, all emissions, stock porting, etc...

The engine was recently rebuilt and I just got thru the 2000 mile breakin. Engine seemed to run a little lean/rough at stock fuel pressures of 37 psi. Now with a walbro I'm getting about 41 psi and it runs alot smoother. Timing is perfect and engine idles well at 800 rpm.

I've had it up to about 6000 rpm and almost 5 psi boost with the stock T2 exhaust and stock GSL-SE muffler. Currently no intercooler cooling but a scoop is next on my todo list. Also I have never had it flood but I use a fuel kill switch most of the time.

I've checked, double checked and rechecked for vacuum leaks and can't find anything. All new hoses and new TID. Injectors were serviced and new grommets used. I think I'll try the water hose trick tonight and see if I can find anything.

I was careful to install all vacuum lines in the way I found them originally but I have in several cases found things not installed right so I suspect I could have something not connected correctly. The wiring is all by the book (FSM). Maybe I'll try and find someone with a S4 T2 in Houston and see if we can compare setups.

Overall I'm pretty happy with this install, but I know this vacuum reading is bad and something is wrong. Soon I'll be putting on a Corksport downpipe and RP high flow cat and I don't want this problem when I go up to higher boost levels.

Thanks in advance for your help.

Scott

 

are you running premix??

usaly low vac is a vac leak. but if it's a sold idle might not be.

I would do a compression test.

 

hmm whats your car idleing at?

because I am getting 12' of vacuum at idle and about 21' of vacuum on a downshift
on some motors its normal
check for a vacuum leak if none found dont worry about it

and most rx7 I worked at and owned had that type of vacuum

 

EGR valve maybe?- rerouting gases back into the intake stream- dunno if that would mess with the vac pressures or not?...don't know how it could be the ACV, unless the little check valve inside there is shot...how are the compression numbers? Maybe you're not quite broken in to the point your vac numbers are where you want 'em...Did you reuse the housings?

 

Yes they are re-used housings. I was told they would still produce acceptable compression.

Guess a compression check is in order.

 

That's what I would do first, to see where to go from there...Just took the kids to Spacecenter-had a blast-costs too much though...LOL

 

Yes about 15 oz per full tank.

 

bump

 

Anybody know?

 

Front rotor and rear rotor both have three solid pulses to 82 psi. Good that the pulses are the same but the 82 psi is rather low.

Procedure: Removed both trailing plugs. Pulled both EGI fuses. Throttle held wide open on a warm engine. Watched pulses while cranking. Used standard compression tester with check valve removed.

What do you think?

 

yeh, that does sound kinda low... same setup I use for my comp tests (although I use the leading plug holes, thinking that the rotor face will be at its highest compression point at that spot), I'm gettin' about 90, but mines on its way to a rebuild in a couple of months, I can tell....

 

I remember reted mentioning something about some standard compression testers reading consistently low. So maybe that could be the cause of the low compression readings? However, with the low vaccum its hard to say.

 

Clogged up exhaust is also a possibility. Vacuum is created through the entire system, high backpressure leaves a lot of air still in there, and the less air being sucked out, means the less vacuum

 

A new cat is going in this weekend.

Anybody else got ideas?

Scott

 

i though compression on tII was supposed to be 85psi give or take upto 21psi according to haynes anyway. just my 2 cents

 

i thought it was 85psi on tII