Here's all the details leading up to this...
https://www.rx7club.com/forum/showth...threadid=99808

I finally had some time to do a compression check and the results were anything but expected. Now granted, I just got the Napa $30 testor, but I removed both trailing plugs, screwed it into one plug hole, removed the ignitor and circuit relay, pushed in the pressure release button on the testor and cranked. It bounced consistantly on 1.5. Out of curiosity, I let the button go, and it climbed to about 5.5. First off, that doesn't make any sense to me. Shouldn't it have bounced to 5.5 if that was the max reading? I tried the other rotor and came up with the EXACT same thing. I also noted that the noise spewing from the empty plug hole sounded exactly the same for each side of the rotor, front and rear. Bottom line is that if I was testing a new car like this, I would have felt like it was fine (other than the low max).

Two things that should be making the test innacurate is that the engine was NOT warm, and I have the battery relocated, so it's tiny and doesn't spin the engine as fast as the old Big Boy.

I also noticed that the two trailing plugs were now black, where they had been brown before the final failure (only leadings were black before).

So any idea what all this means? I can't believe I would have cracked all the apex seals at exactly the same time. It seems like if it were ignition, it wouldn't run at all. If it were the fuel system, it should have shown lean on the wideband O2 sensor. I'm totally baffled now, but I'm starting to lean toward ignition problems. It's essentially running just like other cars I've had when they get a fouled plug. Any ideas would be much appreciated!!!

 

Plug wires in the wrong order will do it...

 

How is the car running now, after the compression test? I read the previous thread, no boost, rough idle. Is it doing the same now?
Thought you might be interested-
My car is @ KD now. The compression was taken numerous times, equal on every chamber,but when the car was driven under slight acceleration the engine would kick back..More compression tests, everything fine..Still problem. Everything checked out fine, fuel, ignition,vacuum,etc. Finally, during 1 compression test, one seal either stuck or cracked, showed a reduced compression for only 1 cycle, then back to normal.
Now having engine replaced. There wasn't enough combustion pressure during compression tests to cause the problem to surface.

 

Shouldn't be plug wires in the wrong order. It all happened while I was driving, so something broke during the high-load, high-rpm run.

That's very intersting, Turbonut. To be honest, I haven't tried starting it again since I got it home, for fear of doing more damage, such as shooting a seal through the turbo or something. But your scenereo seems like a very real possibility.

Thanks for the replies so far!

 

hahaha I know sombody is gonna say something to me about this. But have you checked your MAP senser, if you dont know what this is search. Fouled plugs poor idling, Engine acting like its blown all symptoms of a loose MAP sensor.

 

My feeling is that people are replying because of past experience or the knowledge learned from working on these vehicles. Noone should ever crticize other posts. Hopefully he'll find it to be the MAP sensor.
If it is, we all learned something new.

 

Thanks turbonut - I usually respond to these cuz the same thing happened to me and I thought I blew my engine too.

 

Yup, I realize the original thread was long, but as I said in it I checked the MAP sensor and every other vacuum line, plug, or wire that I can see. Thanks for the idea, though. Hmmm, for that matter, it could be that the sensor went bad even though it's plugged in. But the pressure readings on the PFC would be incorrect if that happened, right?

 

Swap out map sensors with another 3rd gen owner and see if that works

 

I noticed that my car idled a little rough when I got the plug wires cris-crossed. It didn't knock when cruising, but when I put any load or boosted even a little, It would knock bad(169+).

Have you changed spark plugs? I had some new ones in my FD when I first got them, and then they fouled up real quick so I cleaned them up with carb cleaner and a metal brush. I put them in and the same thing...ran like crap and sounded like a blown engine....so I bought new plugs....and the focker fired right up!

 

I'll probably be swapping a lot of parts this weekend. Fortunately the RX-7 crowd is great about helping out...

Thanks for the tip on the plugs. I put a set of brand new plugs in, and they were totally black after 2 miles of driving. Again, the wires should be hooked up correctly since it was running fine, I went out for a run having changed nothing, and suddenly started having problems.

Other ideas? Anyone every had any coil or ignitor failures? I heard that it was common for 93's....

 

I dont know much about the compression tester you got but is it possible that when you hold in the button it leaks??? That would explain why the pressure went up when you let go of the button.

Also, you have 9:1 compression rotors so 1.5:1 isnt good.

What were your air intake temps and how many miles is on this motor?

STEPHEN

 

The MAP sensor might be plugged in, but the hose popped off. This happened to me with the same symptoms. Maybe popped off/split under the manifold?

 

I dont know much about the compression tester you got but is it possible that when you hold in the button it leaks??? That would explain why the pressure went up when you let go of the button.

Also, you have 9:1 compression rotors so 1.5:1 isnt good.

What were your air intake temps and how many miles is on this motor?

Oh yea, where you doing anything with the power fc at the time??? make sure your "options" setting are right in the pfc. If its not on option 1 like it should be it will feel like a blown motor.

STEPHEN

 

stephen, do you mean normal. . . mine was on option 1 one time and it had those symptoms. mine is on normal and it runs fine.

paul

 

can someone be more specific on option one where it is in the menues and what it changes.

 

Anyone please

 

Check the vaccuum hose coming of the bottom of the boost sensor, that little black box mounted on the firewall just behind the intake elbow. Mine popped off and it felt like I blew my motor. Then the hose fell down behind the motor so I couldn't even see it and passed over it many times looking for my problem.

 

start at the main menu: SETTINGS --> PIM VOLTAGE --> NORMAL

Option one give you the option to run a GM 3 Bar Map Sensor to boost higher than 1.2 safely since the stock FD map can't register anything over 1.2 well.

 

Thanks for the other tips. Yeah, the MAP sensor had both the plug and the hose still attached to it, and my PFC was still on "Normal". Good tip, though, as I accidentally moved it one time and the car wouldn't run. Wasn't touching anything on the PFC at the time, so I don't expect it was a setting.

I don't remember the exact air intake temps, but my guess is that they would have been in the 40s or 50s. I just remember they were normal at the time. The engine had around 50k miles on it, and I can't attest to how it was treated during that time since I only owned it for the last 20k.

Checked the ignition and it was still good too. Drove it a little more and aside from the shaking is the significant loss in power. At the end of the drive there was a loud knocking noise coming from the center of the car. I gotta have this thing back before the fall MADS, so it's gettin' towed tomorrow morning to Rotorsports Racing to let the experts have a crack at it!

Thanks again for the replies.

 

It could be..
1)Bad leading coil
2) bad plug wire/s
3) plug wire coming off coil or spark plug
4)clogged injector
5) Bad thermal sensor on back of the H20 housing (TX40) for cross reference at your local advantage auto store.
6)cut in boost sensor hose
7)leading coil wire came unplugged or is severed/cut.
8) grounding issue on one of the wires from the main harness...(doubtful).
Do a code check and Good Luck....

 

What kind of knocking??? Was it real loud? did it only do it where you have loss of power? Was there a pattern to the knock???

If you get out of the car and listen can you get a better idea of where it was at?

STEPHEN

 

Again, as a last ditch effort, I verified that the leading plugs had spark, so I think that ruled out the ignition related problems.

The knocking was VERY loud after my drive. I got out of the car and walked around and it came from right in the middle of the car, behind the engine. It corresponded with the frequency of the shaking, and with the RPM of the car. Anyways, as of 7 this morning it's been towed to the professionals........

I'll let you know what it turns out to be.

 

Well, maybe its something to do with the flywheel or clutch.....busted flywheel maybe??? I dont know.

I remember Spyfish007's car knocking real bad like that when his e shaft cracked but he couldnt start the car back up so I dont think thats it. Your not smoking.

Did you pop the hood while the knocking was going on? Was the engine jumping around real bad or anything like that? Its very unusual, definatly keep up posted

STEPHEN

 

I had never heard it before, but Bryan at Rotorsports Racing said that he had seen the ring gear separate from the flywheel on SR flywheels before (which is what I have). But I never heard anthing pop or break and I think it would have mades ome noise spinning around in there at 8000rpm!

Yeah, I popped the hood while the noise was happening, and the engine wasn't visibly moving. You can just feel it throbbing through anything mounted to the body. Crawling around the car on hands and knees seemed to indicate the noise was coming from under the car just behind the front wheels.

Bryan cranked it up and said at least initially he thinks it's the engine. Should hear something definitive around the middle of next week.