KA-T Compression test numbers--question

[vinnyjdm]

So I have been building my car for a long time now and just did the first start. It wouldn't stay idling and the fuel pressure was reading 100 on my isis FPR. Definitely running rich as fuck, I tried adjusting it but regardless of my adjustments to the FPR the pressure wouldn't change.

Anyhow,

I did a compression test and the numbers were as follows
Cylinder 1: 144
Cylinder 2: 155
Cylinder 3: 156
Cylinder 4: 164

As you can see, there is a 20PSI different between cylinder 1 and 4. Should I be concerned here?

Any help is appreciated!

http://i58.tinypic.com/vsdeup.jpg

http://i59.tinypic.com/mrcwif.jpg
http://i62.tinypic.com/ivedk8.jpg
http://i58.tinypic.com/qqpjkg.jpg
http://i57.tinypic.com/xlwcgw.jpg

[Kingtal0n]

yeah something is wrong. do a leakdown test and see if you can hear anything in the exhaust or intake side that would indicate a valve problem on number 1-3.

Likewise, #4 being so high, check it for signs of oil, oil raises compression (which is why it helps cause detonation/knock).

[vinnyjdm]

I'll try to do a leak down test also just to see what the results are but i'm gonna have to try to get an air compressor and find the tool

I read on a thread on nicoclub saying each cylinder should be no more than 25psi of each other but I just wanted to verify that. If thats the case I think i'm okay (hoping I am)


I did a mild rebuild on the motor, it came out of my neighbors car and I replaced the head gasket, head studs, front & rear main seal, etc. before I dropped it in my car. Definitely don't wanna tear apart the motor again. I'd buy another KA before I did that again

[Bleakley]

Ideally you want compression within 5-10% across all cylinders, but iirc 15% is acceptable. An engine will run at 20% differences.
Your fuel pressure might be the problem. You need a way to measure it and I'm wondering if your mechanical gauge isn't cutting it or something..
The vacuum line should be referencing boost/vacuum (behind throttle plate).
Dumb question, but have you verified fuel is returning to the tank? Check your regulator and connections are returning fuel to the tank. If not, that's why you're at 100 psi no matter the adjustment..

[EDacIouSX]

yea I don't see a vacuum line in the picture but it's REALLY hard to tell.

should look like this. make sure the FPR is pulling vacuum from the right spot

http://gallery.rennlist.com/albums/album591/Aeromotive_FPR.jpg

[kruked]

4th & 5th picture shows that his vacuum is hooked up correctly on the FPR.


Bleakly is correct, you don't want more than a 15 PSI difference between ALL 4 cylinders. A lot of us know though that we've seen way more of a difference, and have still seen a car function.

[vinnyjdm]

Okay, well I will get the car running properly and see how it functions with the compression how it is. I haven't gotten to car to actual operating temperature to check it because the car won't idle (assuming because of the fuel pressure issues.)

Bleakly: Yeah I know the fuel is returning to the tank because when I turned on my fuel pump the first time I saw fuel leaking from the fuel filter return and had to replace the fuel filter

EDaclouSX:I do have my vacuum hooked up properly on the FPR. I tried adjusting the fuel pressure on the FPR and if i spin the adjuster screw either way nothing changes with the pressure. who knows what it really is because the gauge only reads up to 100psi. could be more!

2 concerns for me:

1) I purchased the FPR 'Open Box' so i'm wondering if it might be defective.

2) Also wondering if I have a stuck open injector or something, not sure if that would effect fuel pressure or not though, or if I would still be able to adjust it at all.

Can't think of anything else that could be the issue. The fuel pump is a brand new walbro 255 and i have a brand new fuel filter

[greenwood]

Replaced the fuel pressure unit.

Change oil and filter after you get it running as the oil is probably full of gas.

[kruked]

Pull the fuel rail w/o disconnecting the injectors. Place a piece of cardboard under the injectors and turn the engine over for a second or 3. Make sure that all of the injectors are spraying. Make sure that none of them are leaking w/ the key in the "ON" position.

I would lean more towards the FPR.

[vinnyjdm]

4th & 5th picture shows that his vacuum is hooked up correctly on the FPR.


Bleakly is correct, you don't want more than a 15 PSI difference between ALL 4 cylinders. A lot of us know though that we've seen way more of a difference, and have still seen a car function.

Based on your experience do you think the motor can still be healthy/run healthy with this difference?

I'm hoping that when I actually get the car to operating temperature and with oil properly dispersed through the motor it will even out.

[jr_ss]

My suggestion, buy a better gauge and redo the test. Also I recommend getting the car to the point of running. Your engine may be fine but without bringing it up to temp your readings are kind of pointless.

[KAT-PWR]

The motor can run, but under anything fair amount of boost i will bet the engine does not last very long.

[vinnyjdm]

I'm gonna be running 12lbs of boost. I'm gonna get the fuel situation figured out and get the car running and then retest

[kruked]

Do you think the motor can still be healthy/run healthy with this difference?

Your compression is the least of your worries right now. If anything figure out what's the actual problem w/ your situation, then do another compression test. Your numbers might be better.

Is there a way that you can put a stock FPR regulator back on your setup w/o disrupting anything major? It would be your cheapest alternative then buying another FPR (aftermarket).
You did mention that your current one was an "open box". That aught to be the first suspect component.


The motor can run, but under anything fair amount of boost i will bet the engine does not last very long.

Not always true, brother.

[vinnyjdm]

I told enjuku about the FPR issue (i bought it from them) they said they are gonna send me another one. Stay tuned for updates! Thanks for the help everyone

[KAT-PWR]

With all that fanciness you did do a new headgasket and arp head studs right?

[vinnyjdm]

With all that fanciness you did do a new headgasket and arp head studs right?

haha yes I did a felpro head gasket and ARP head studs. Wanted to do a metal head gasket originally but the felpro is rated for 400 HP and my tune is setup for 300whp on 12 psi so I'm not worried about it

[EDacIouSX]

its really weird how cylidner 4 is the highest... usualyl its the other way around, 1 to 4 is highest to lowest. Anyway... if you have a good tune you should be fine, you will just make less power.

KEEP IN MIND, i am not a professional so i could be wrong lol.