BoOsTin FD

I kind of started talking about this in somebody else’s thread, but i really got nowhere.



Here is the story...



I drive the FD maybe once or twice in two weeks. I usually drive it around for like 30-40 min with like 1-2psi of boost before i even get really on it. I admit i do drive this car like i stole it. My mods are the following: Huge Street port with 4k miles on it, rebuilded with Mazda factory parts, Rebuilded stock twins with 9k miles, PFC tuned for 1 bar. PFS SMIC, Dp, Hi-flo (which I think is clogged) Catback, Supra fuel pump, 1300cc secondaries, MSD 6a going to Leading coil. Removed all emission stuff, Pulleys, some braces etc. The car ran great for a year in these 4k miles.



Saturday night, I went for a drive. I’ve been driving it for like an hour before I started boosting it. I redlined it couple of times, got 15psi everything was great. I drove it afterwards everything perfect. So later on I went on highway on my way home, I was driving it normal, then I tried to pass this truck, so I dropped it to third gear, I redlined it again and went on. 5 minutes after I came to my exit ramp, I stopped on the signal light and the engine started sounding like it’s blown.



These are the symptoms I got: Vacuum reading 10-12, Idles weird like on 1 rotor, kind of shakes, Smells like unburned fuel coming from exhaust, has no power from the start to like 3-4k. Then it pulls hard.



Things I checked so far: Compression I tested by using piston engine tester, for each rotor I got 3 even spikes of the needle in the 35-40psi range. Overall compression when I let of the bleed valve to build the reading I get on the front rotor: 89-95psi. Rear rotor: 100-105.



I bought brand new wires and spark plugs, Checked Fuel injectors, and coils… which turned out to be fine. Map sensor I replaced because I had spare and I changed the hose going to it, still the same. With it unplugged it runs even worse. Spark plugs when they were taken off, 2 were brown and the ones going through MSD were a little black like rich. There is no oil on sparks or antifreeze.



Each spark plug is getting spark, I even tried bypassing the MSD and I still got the same problem. What I did notice about the sparks is that when I unplug the L1 the engine runs the same crappy way with it or without it, I mean there is no difference. Every other one I unplug it runs even worse. T1 when I unplug the spark plug wire, the sparks start shooting at the top of the coil rather then down at the end of spark plug wire.



Now all this might have been like this forever and I the car ran great without any problems and I’m just noticing these things now. I highly doubt that even if one coil or one side of the coil is bad it would give me all symptoms of blown engine. When I tested the coils they showed everything to the spec like it says in the manual.



I really don’t know what else to do at this point… I don’t have access to Mazda Compression tester, and I’m not taking it to a dealer because they screwed my FC last time I took it there for compression test.



Anybody has any other suggestion on what I should check. If you have been at this situation and you can give me some input if it is the engine or if it’s something simpler.



Thanks a lot.

rfreeman27

remove the bleeder valve from a compression checker.



If it does not spike high, then chances are your motor is blown.



you are running a good bit of boost/mods for the stock fuel system.

BoOsTin FD

my fuel system is not stock. I wrote on there that i have supra fuel pump, 1300cc secondary injectors, 550 primary. At 15psi i get 71% inj duty.



I did take the valve out all the way when i watched for bounces and as i said i got 3 even in between 35-40psi range.

rfreeman27

lol sorry i skimmed.



Um yeah that is low...



who did the motor?

BoOsTin FD

well the sweep should be in the 30-35psi range because it doesnt have time to build because it's letting the air out of the tester.



My overall compression test using this thing was 90 on front and 100 on the rear.



any other suggestions? Could the CAS sensor do something like this?

rfreeman27

Its not about overall pressure.



It Should SPIKE to 90 or higher for a good motor

BoOsTin FD

I followed this test.



Compression test using a piston engine tester:

1. note battery strength. A weak battery will yield low compression results.

2. Remove both lower plugs and wires.

3. remove EGI fuse from engine fusebox.

4. have a friend floor the accelerator pedal, opening the throttle for more airflow

5. insert your tester into the leading hole

6. hold the valve on the side of the tester open

7. have your friend crank the car over for 5+ seconds.

8. observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range.

9. let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment.

10. repeat for opposite rotor. Note difference in overall compression between rotors, which should be no more than 20psi max.



you can find it on this website by going to tech section.

http://www.rotaryresurrection.com/



It doesn't say it should spike in 90psi range.

sweet7

Who did the motor?

BoOsTin FD

it was done by my buddy and me.



The engine was fine for a year... i really can't believe it blew.

GreyGT-C