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ECMlink Low, fluttering vacuum at idle.

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A Sharp

Proven Member
158
13
Nov 18, 2013
Platteville, Wisconsin
This is for my 2g rebuild.

1). Any boost, vac, or exhaust leaks?

Boost leak tested 5psi above your max boost with no leaks?
I BLT'd the throttle body. Found a big leak by an injector. Fixed it, but didn't really help the problem.

2). Verified mechanical timing?
See below.

3). Verified base timing?
No

4). Ignition system
COP or Stock Coil: Stock
Wire brand and Age: New (forget brand)
Spark Plug brand, type and Gap: NGK 6's -- gapped to .028

5). Motor health (Compression Test)
Cylinder 1: 150
Cylinder 2: 150
Cylinder 3: 150
Cylinder 4: 150

6). Performed basic throttle body adjustments?
Idle Switch: Simulated through link
Throttle Cable: yes
TPS: yes
BISS: yes

7). Compression ratio
About 9.0:1 to 9.5:1. I did a stock rebuild on the shortblock. The machining probably added a bit of compression.

8). Any known bad sensors or brittle wiring?
I wouldn't doubt it.

9). Any DTC/CEL codes?
Emissions stuff. Nothing important.

11). Base fuel pressure and injector values
Base Fuel Pressure: 43 PSI
Injector Size (cc/min): 1000cc PTEs

12). Properly calibrated and configured wideband sensor
Sensor Brand: LC1
Calibration Date: A few weeks ago

13). Type of fuel
Type: e85
Percent of Ethanol: Haven't tested it yet, but my fuel trims indicate that it is probably close to 85%.


I have super low vacuum at idle. About -7 inHg at 1000 RPM. Also, the vacuum gauge looks like it's having a seizure. Check out this vid:
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As you likely notice, the vacuum acts normally at higher RPM. I was thinking this problem was caused by improperly degreeing my cams. I've got Web 276/274's. They are about on par with a lot of 272's out there. This is my cam card

http://www.webcamshafts.com/pages/automobile/mitsubishi/install_data/tc_000357_000864.html
I have since tried decreasing overlap and playing with the cam gears in various other ways. None of the adjustments made a significant difference.

I have not verified base timing, since I have a crank sensor and a 97+ cas. However, I have a tried advancing the timing a few degrees at idle. It seemed to help a bit. My ECU is a '95, just FYI.

When I BLT'd the intake manifold, I fixed a large injector leak. It didn't help, though, and I can't find any other leaks. Also, I noticed that pressure slowly escapes into my crank case. Probably due to my rings not being fully seated.
The throttle body was recently rebuilt. The FIAV is screwed all the way down and an EGR blockoff plate has been installed.

I wouldn't care about this problem, but it can make braking scary. I noticed it when I was coasting in neutral. The brake pedal got really hard after touching the brakes a few times. My cams aren't that huge and I have decent compression, so what gives?

Edit: added a log of running it in the garage. BTW, I am aware that my TPS liked to stick at 1% sometimes during this log. I'll be fixing that.
 

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The engine seems to running well, so maybe I'll just buy a vacuum canister and call it a day. Seems like a bandaid fix though :hmm:
 
I installed a vacuum canister and bumped the idle/timing up a bit. Braking is fine now. I also did a blt from the turbo inlet up to 18 psi, which is where my uncrushed bov starts to open.

The root issue still exists, though. Has anyone had any experience with these cams?
 
It can very well be your cams. I ran a set of Graveyards grinds and my vacuum was similar. I swapped those out for some FP2s and my vacuum was back in the high teens.
 
My Kelfords are that way at idle also.
 
Glad to hear that I'm not the only one who has seen this. It seems like everyone with BC's or FP's is reporting around mid teens.
 
I'm lucky if I have -8hg.
If it didn't run so dam good I would worry about it. I really think that obviously in my case it seems to be valve overlap but tune can play into it also so don't rule that out. If I play with deadtime I can change it a little so you could play with it and see if it likes a little more or a little less. I do. On a carb, low vacuum comes from valve over lap AND timing. I'm assuming you have tuning software and if so, play with those but know where you started so you can go back to that if you need to. I'm not scared to play with my car's tune just to "play" :)
 
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