I did a compression check on my S5 T2. I really just checked the rear cylinder. I removed all of the plugs, screwed the compression checker into the trailing plug of the rear rotor and cranked the engine. But, I didn't get any compression.

So, I screwed the leading plug in tight and then cranked it over and I got about 95 lbs.

Shouldn't I get a compression reading with all of the plugs removed and the checker in the trailing plug?

thanks, ashley

 

I'll let the cylinder comment slide since you're a girl (or at least have a girl's name).

If you remove the trailing and leading plugs, then screw the tester into only the trailing plug hole, you will always get 0 psi. When the rotor passes over the open leading hole, all of the air will rush out. It will not be compressed, which means no reading on the gauge. Both plugs lead into the same combustion chamber, so it's not like each one is for its own cylinder like in a piston engine.

 

u need to take the shrader valve out of ur compression tester hose and only remove trailing plug u should see the needle on the guage jump 3 times to about 90psi at 300rpm (thats about what the starter does) so as long as u dont have 2 jumps to 90 then 1 to 30 u should be good

 

Small correction, if an apex seal is blown, you would get 2 small readings and 1 normal reading.

 

Yes, I'm a girl but this is not my first 7. I just wasn't paying attention to my wording. I've had an 86 NA, an 87 NA, an 88 T2, an 87 T2 and now I have this 90 GTU / T2 conversion. All were 5 speeds.

I don't remember ever doing a compression test. I rebuilt the 87 NA and the 87 T2 but never checked the compression.

Does porting effect compression results? My Dad was told that this motor had been ported but I'm starting to think everything the guy told my Dad was a lie. I didn't take out the valve but the apex seals are all in place. The compression is only like 92-95 lbs total. My Dad was told that the motor had "recently" been rebuilt and was ported during the rebuild and the rotors had been machined to accept 3mm seals.

thanks for answering my question

ash

 

Make a few laps around the block first.

Pull the EGI fuse under the dash to it won't start, compression test should be done with the engine warmed up, one top plug at a time, and the throttle wide open. Rather than remove the shrader valve just hold down the relief botton and watch it bounce.

When I did mine shortly after completing my swap I got over 100 psi on all 6 bounces (3 per housing). From what I've read if you're 90 or above you're okay. I do not honestly know but I would guess that porting shouldn't make a difference in the compression, and if it does it would depend on what type and how extreme the porting was (ie: exhaust, intake, bridge port, mild/wild/extreme size)

 

Porting shouldn't harm or help compression.

 

+1

 

since no one has asked i will why do u think u have a compression issue ????

 

I'm not sure what the problem is. I have an s5 gtu/t2 swap. Will not idle, as soon as you take your foot off the pedal it dies. We just swapped out the motor because the previous owner blew the rear apex seals. I'm told that the motors are both 1990 T2 but I can't verify the year but they are S5. The PO said the motor ran great until it died.

I know that failing to idle points to a vac leak, but I can't find one.
But, I'll keep looking.

ash

 

what computer are u running ? and is it jspec or uspec turbo ?

 

Have you set the timing, tps, idle set screw, and adjusted the throttle cable tension since the swap?

 

Uspec. The computer is doesn't have a label.
One thing that I noticed different between the 2 motors is they have different air intake thermosensors. The blown engines sensor is small( maybe 3/8 inches round and about 1.5 inches long) and the other engines is larger(about 7/8 by 2) and they have different connectors also.

ash

 

Throttle cable tension is OK, tps is OK, the only idle adjustment is the adjusting screw toward the firewall and its all the way in. I haven't had anybody here to give me a hand at the timing, I need somebody to hold the throttle for me. I'll give that a go in a little while.

Thanks for the suggestions.

ash

 

This is the best way to test compression:
pull the EGI fuse
remove all 4 spark plugs
hold the gas pedal to the floor and crank the engine

If the engine makes even WHOOSH WHOOSH WHOOSH WHOOSH WHOOSH WHOOSH it's good. There are 6 compressions before the cycle repeats and every one should sound the same.

If the 6 pulses are not even then the engine needs a rebuild. A common rebuild rhythm would be WOOSH WOOSH woosh woosh WOOSH WOOSH

 

Where in PA are you? If by Pitt Med you mean University of Pittsburgh, which I assume you do, you're not far from me. I'm in Washington. I don't know any rotorheads in my area.

 

This sounds aftermarket. Just for reference the stock IAT is tiny, on my haltech I drilled out and re-threaded the sensor location because it was that much larger. How does the throttle body look? Thermowax gone? Is the throttle stop screw backed out?

But yeah... vacuum leaks.

 

If its not idling right, check for vacuum leaks.

 

does it run ok if u keep it running and just wont idle or does it run like crap and not idle

 

Hi, I attend PITT ( University of Pittsburgh). Eventually, I'm going to be an MD, probably Neurosurgery. I live in WV. My Dad bought my T2 motor in Washington.

ash

 

Thanks to everybody that helped. The T2 had two problems: First was the vac leak at one of the fittings on the front intercooler and then it was also way out of time.

Now I need to find the reason behind the low oil pressure. It has about 40 lbs at 4000 rpm but only about 5 lbs at idle. I'm pretty sure that on the last rebuild I did I had about 60+ at 4000 but I don't remember about the idle.

ash

 

Idle should be at least 20psi and 4k rpms should be about 80psi. What gauge are you looking at? The stock one can't be trusted. I would install a mechanical gauge and run a plastic line from the block to the gauge.