Comression Results (Cranks, but No Start)
04-19-14, 11:17 AM
#1
Comression Results (Cranks, but No Start)
Hey guys, so I recently bought a 2nd FC for parts. It's a 1990 GXL with 622,xxx miles on it. No thats not a typo, I was told it had 4 or 5 engines in its life. When i got it from a dealer the car drove fine, no smoke at higher rpms, no problems at all. I drove it home for about 60 miles with no problems. Parked the car, tryed to start few days later and i got nothing. It cranks, but no start. I should mention that there is white smoke coming out the exhaust if cranking for extended period of time.
Anyway Im not too familiar with rotaries, so I decided to start from the basics. Compression, Fuel and Spark.
For compression I disconnected fuel pump connector by the rear strut tower. Used a remote start to bypass spark. Here are the compression results:
cylinder closest to firewall - 85psi on 1st puff, 145psi final
cylinder closest to front - 50-70psi on 1st puff, 110psi final
Now I read here in forums that the minimum is anywhere from 90-100psi, but it still kind of worries me. Also i did notice coolant smell and wet spark plugs when i pulled them out.
I tested the spark. Bought one of those ignition light testers from parts store that connects inline between spark plug and wire. I did get spark on all 4 spark plugs at cranking speed.
For the fuel pressure I T'd the gauge between the filter and the main fuel line. Jumped the two wire connector. With the key on I got 40psi, after 5 minutes it dropped to 37 psi.
Phew... thats a lot of writing. Anyway my biggest concern is the compression. Is 50-70psi on 1st puff, 110psi on final enough to cause a no start? I am getting a repair manual and will start testing with one of those buble charts for "No Start, But Cranks". Just want to get some thoughts on comression results before i start.
Anyway Im not too familiar with rotaries, so I decided to start from the basics. Compression, Fuel and Spark.
For compression I disconnected fuel pump connector by the rear strut tower. Used a remote start to bypass spark. Here are the compression results:
cylinder closest to firewall - 85psi on 1st puff, 145psi final
cylinder closest to front - 50-70psi on 1st puff, 110psi final
Now I read here in forums that the minimum is anywhere from 90-100psi, but it still kind of worries me. Also i did notice coolant smell and wet spark plugs when i pulled them out.
I tested the spark. Bought one of those ignition light testers from parts store that connects inline between spark plug and wire. I did get spark on all 4 spark plugs at cranking speed.
For the fuel pressure I T'd the gauge between the filter and the main fuel line. Jumped the two wire connector. With the key on I got 40psi, after 5 minutes it dropped to 37 psi.
Phew... thats a lot of writing. Anyway my biggest concern is the compression. Is 50-70psi on 1st puff, 110psi on final enough to cause a no start? I am getting a repair manual and will start testing with one of those buble charts for "No Start, But Cranks". Just want to get some thoughts on comression results before i start.
04-19-14, 11:53 AM
#2
It sounds flooded man. I would go ahead crank the car without spark plugs and disable the fuel pump to clean all that fuel inside the chamber. After that install a new set of plugs, hook everything back up and turn it on with a fully charged battery. Give that a try first the way your explaining compression number don't sound clear to me. I would say 90 psi minimum of compression is the benchmark for a engine to function. Any lower I would question a rebuild ?
If your smelling coolant inside that might be a bad sign of overheating maybe coolant seals is there anything that lead to possibly a temp gauge not working or fan, etc, etc....
If your smelling coolant inside that might be a bad sign of overheating maybe coolant seals is there anything that lead to possibly a temp gauge not working or fan, etc, etc....
04-19-14, 03:47 PM
#3
Your description of compression is confusing....first puff? Are you taking an over all compression instead of each rotor face? Or something else that is not making sense? It almost sounds like ypu have 2 weak sides of a rotor than a strong side, which if thats the case, your probably gonna have flooding issues dues to low compression. If it were me i would be preparing to rebuild before more damage is done, or make it a luck #6 engine
04-20-14, 09:20 AM
#7
You need ti have three even pulses. NO MORE than 8psi variance between faces or rotors, nothing under 90psi per face. Below 90 you encounter flooding issues. You CAN use a piston tester, you just need a friend to crank it while you hold the shrader open. Also, you can cut fuel and spark at the same time by unplugging the Crank Angle Sensor. It's sticking out of your front cover, it's round like a distributor and has a flat, black top with the three-wire white plastic plug on one side.
When you pulled wet plugs, did it reek of gas? If not, you need to do a coolant pressure test. It should go no lower than 13psi and hold from testing pressure of 15psi.
When you pulled wet plugs, did it reek of gas? If not, you need to do a coolant pressure test. It should go no lower than 13psi and hold from testing pressure of 15psi.
Trending Topics
04-20-14, 12:27 PM
#11
I want some guru input here myself. It involves spinning the CAS by hand.
There is another method to find out if you have a problem with your wiring. You should check voltage at the plug, resistance at the plug and continuity between the plug and the ECU. F everything is gravy there but you still feel like there's a problem, I did this. See if it will idle fine. If not, find the pins for the primary injectors. Pull one out while it's running [but please be careful]. If it doesn't stall, stick it back in and pull the other. If it stalls now, the OPPOSITE plug is what's wrong. You can do the same with the secondaries, only pull and label both primary wires, and put the F and R secondary pins in their respective primary slots so it will be running on just the secondaries at idle. Pull and check.
There is another method to find out if you have a problem with your wiring. You should check voltage at the plug, resistance at the plug and continuity between the plug and the ECU. F everything is gravy there but you still feel like there's a problem, I did this. See if it will idle fine. If not, find the pins for the primary injectors. Pull one out while it's running [but please be careful]. If it doesn't stall, stick it back in and pull the other. If it stalls now, the OPPOSITE plug is what's wrong. You can do the same with the secondaries, only pull and label both primary wires, and put the F and R secondary pins in their respective primary slots so it will be running on just the secondaries at idle. Pull and check.
04-23-14, 11:57 PM
#12
So, I just did a coolant pressure test. It held 15 psi for 10 min without dropping. I even tryed cranking the engine with remote starter while testing and not single psi dropped.
Than however I did pull the spark plugs out and noticed coolant on spark plugs again. So I'm pretty sure the seals are bad.
I did rechecked my compression while holding down the release button on my tester. I got even pulses for both cylinders. The one closest to firewall had around 80 psi with even pulses. The one closest to front had around 50 psi with even pulses.
Than I tryed to clear the fluding out by removing top spark plugs and just cranking with remote control. There was a mist that blew out. I than recharged the battery and connected everything back in. Tryed to start the car but still nothing.
Are those results sufficient? Are the cylinders low on pressure? Do I need to get a special rotary tester for compression?
Than however I did pull the spark plugs out and noticed coolant on spark plugs again. So I'm pretty sure the seals are bad.
I did rechecked my compression while holding down the release button on my tester. I got even pulses for both cylinders. The one closest to firewall had around 80 psi with even pulses. The one closest to front had around 50 psi with even pulses.
Than I tryed to clear the fluding out by removing top spark plugs and just cranking with remote control. There was a mist that blew out. I than recharged the battery and connected everything back in. Tryed to start the car but still nothing.
Are those results sufficient? Are the cylinders low on pressure? Do I need to get a special rotary tester for compression?
04-24-14, 10:23 AM
#16
I did not get the chance to start/drive the car for too long. Just drove the car at dealer test drive and drove it home from the dealer. Than it just would not start. I did however notice white smoke out the tail pipe when I'm cranking for more than 5 sec.
04-24-14, 02:23 PM
#20
Your not doing your compression test correctly. Pull the egi fuse. Insert tester into a leading hole. Remove the valve in the tester or hold it down through out the whole test. Have a friend crank it over for you.
Each needle bounce is a face of the rotor. There should be 3. If there is less bounces (a pause between), you lost an apex seal.
Repeat for each housing. Post results for review.
Edit: read posts and saw your results. You can try adding normal rotary safe engine oil or premix oil in through the spark plug holes and see if that makes a difference, but it sounds like you need a rebuild. 80psi is on your way out. 60 is bare minimum to kinda sometimes run. 90 or better is healthy. Dealer fucked you. I would make gem take it back due to lemon law, or renegotiate.
Each needle bounce is a face of the rotor. There should be 3. If there is less bounces (a pause between), you lost an apex seal.
Repeat for each housing. Post results for review.
Edit: read posts and saw your results. You can try adding normal rotary safe engine oil or premix oil in through the spark plug holes and see if that makes a difference, but it sounds like you need a rebuild. 80psi is on your way out. 60 is bare minimum to kinda sometimes run. 90 or better is healthy. Dealer fucked you. I would make gem take it back due to lemon law, or renegotiate.
04-24-14, 03:37 PM
#22
Doubt a seal would let go as soon as he gets it home. edit...I mean engine seal...maybe they're worn or a bad coolant seal. But I'm no expert lol.
Your compression readings will be lower:
- with a cold engine
- if you've flooded it and there's no oil on the housings
- with a piston type tester holding the shrader valve open
As mentioned, do the above mentioned regarding removing spark plugs, unplugging CAS, cranking, waiting for fuel residue to evaporate, adding oil (a litl, like an oil can squirt), then new plugs and cranking with a fully charged battery.
edit: I used to always forget, when compression testing hold the throttle wide open.
edit some more:
Checking injectors:
1. Ign. on.
2. Take out CAS from front cover (CAS is the distributor looking thing but with a top round plate with no spark plug wires lol). Held on with a nut, sometimes a plastic tamper resistant clip on the threads.
3. Get a helper to spin CAS
4. Have an auto stethoscope with its rod going past intake runners and all that **** above the engine and touch each injector which is mounted to the top of center housing. Those are the primary injectors. Each one should be clicking in sequence. Don't worry about the secondary injectors (the ones easily seen). They don't activate/work/click when starting (they work above "x" RPM under certain manifold pressure).
Your compression readings will be lower:
- with a cold engine
- if you've flooded it and there's no oil on the housings
- with a piston type tester holding the shrader valve open
As mentioned, do the above mentioned regarding removing spark plugs, unplugging CAS, cranking, waiting for fuel residue to evaporate, adding oil (a litl, like an oil can squirt), then new plugs and cranking with a fully charged battery.
edit: I used to always forget, when compression testing hold the throttle wide open.
edit some more:
Checking injectors:
1. Ign. on.
2. Take out CAS from front cover (CAS is the distributor looking thing but with a top round plate with no spark plug wires lol). Held on with a nut, sometimes a plastic tamper resistant clip on the threads.
3. Get a helper to spin CAS
4. Have an auto stethoscope with its rod going past intake runners and all that **** above the engine and touch each injector which is mounted to the top of center housing. Those are the primary injectors. Each one should be clicking in sequence. Don't worry about the secondary injectors (the ones easily seen). They don't activate/work/click when starting (they work above "x" RPM under certain manifold pressure).
04-24-14, 07:47 PM
#25
I played 2100. This was back when it was running like a champ. The interior is 9-1/2 out of 10, black. Which was the main reason why I bought it. I'm going to do a swap with my ugly blue s4 interior. Also I wanted to do an s5 body swap and some parts like sunroof motor and stuff.