390SE Compression Test Values
Discussion
Hi Folks,
Does anyone know what sort of values each cylinder should be on a 390SE (NCK engine) please?
According to the mighty google and a number of different online calculators the values for a 10.5:1 engine should be in the region of 154psi but mine are way over that, even the lowest reading suggests an 11.66:1 compression ratio so I'm confused.com.
Jase.
Does anyone know what sort of values each cylinder should be on a 390SE (NCK engine) please?
According to the mighty google and a number of different online calculators the values for a 10.5:1 engine should be in the region of 154psi but mine are way over that, even the lowest reading suggests an 11.66:1 compression ratio so I'm confused.com.
Jase.
That "seafoam" stuff is supposed to be good for clearing out coked-up engines.
Having said that I've never used it, and don't know anyone who has, personally.
But the idea is that you run the engine nice and hot, then on a fast idle spray in water, then don't stop the engine and take it for a run to dry it out.
Interesting that 1 and 8 are high - I did hear that the end cylinders tend to be different but now I can't remember if richer or leaner.
Maybe stick a boroscope into 1 and 8 to take a look?
Having said that I've never used it, and don't know anyone who has, personally.
But the idea is that you run the engine nice and hot, then on a fast idle spray in water, then don't stop the engine and take it for a run to dry it out.
Interesting that 1 and 8 are high - I did hear that the end cylinders tend to be different but now I can't remember if richer or leaner.
Maybe stick a boroscope into 1 and 8 to take a look?
154psi is suspiciously 10.5 x 14.7 so all they've done is multiply atmospheric pressure by the compression ratio, that's not how it works. On the one hand you've got the poor trapping efficiency of a slow turning engine and valve events not immediately at top and bottom dead centre, and you've got the heating effect of compressing a gas increasing its pressure.
Your figures are fine.
For reference a high compression engine (say around 10.5 to 11 to 1) would be well over 200psi. (cerb ajp8 regularly measure 215-220psi for example on a compression tester)
Your figures are fine.
For reference a high compression engine (say around 10.5 to 11 to 1) would be well over 200psi. (cerb ajp8 regularly measure 215-220psi for example on a compression tester)
Thanks for the replies, I haven't had chance to look at it today but will give it a good coat of looking at tomorrow.
The reason for doing this was to try and figure out why it runs so bad. It's never ran right since I have had it, the guy I bought it from stored it in a carcoon for about 8 years. I re-commissioned it but I am stumped!
I have checked all the sensors quite a few times and replaced quite a few of them, the ECU was repaired/re-soldered by CES back in 2005 (from memory as it's before I got it), I have checked the earths and wiring and gone through the vintage model airplane website checks. I have had the injectors checked cleaned and flowtested, the pump, filters and fuel pipes have all been changed, it's got a new fuel pressure regulator (rising rate) fitted and I have checked for air leaks etc. I sent the AFM off for assessment and repair (that completely screwed it up by the way), it was so rich it was like an old steam loco! I leaned the mixture off inside the AFM after speaking to Dom at Powers Performance who originally set them up from new.
Symptoms are :-
1. Test's lean on MOT Test Emissions machine and tests lean on Gunsons Gas-tester at home.
2. Plugs are thick black sooty, Tailpipe is thick black sooty (indication it's rich)?
3. Absolutely stinks (I mean really bad like tear gas - it's so acrid that it chokes you) when running, it's so bad the neighbours up to two houses up and down the road close the windows when it's running in the drive and you have to go and have a shower after you have put it in the garage (Indicating its rich).
4. Will start first turn of the key but you have to feather the throttle and keep the revs at about 1800rp until warm other wise it wont tick over (indicates its lean)?
5.Used to run out of steam around 4000rpm where it would cough and splutter and backfire. The rising rate FPR helped with this (indicates it's lean)?
6. Idle mixture screw doesn't seem to do a vast amount to the mixture, I can manage to get it up to 1.2 co and that's about as far as it will go.
I have done a leaktest and the head gaskets are OK as far as that will tell me (I thought maybe if they were tin gaskets and it hadn't ran for years it maybe them but no). Compression tests are as I have posted and the breather system seems fine.
I have the opportunity to borrow/buy someone's 390se ecu and afm next week as I can only think it's an ecu fault.
I am open to any suggestions from you guys as I am ready to push it off a cliff at present.
Jase.
The reason for doing this was to try and figure out why it runs so bad. It's never ran right since I have had it, the guy I bought it from stored it in a carcoon for about 8 years. I re-commissioned it but I am stumped!
I have checked all the sensors quite a few times and replaced quite a few of them, the ECU was repaired/re-soldered by CES back in 2005 (from memory as it's before I got it), I have checked the earths and wiring and gone through the vintage model airplane website checks. I have had the injectors checked cleaned and flowtested, the pump, filters and fuel pipes have all been changed, it's got a new fuel pressure regulator (rising rate) fitted and I have checked for air leaks etc. I sent the AFM off for assessment and repair (that completely screwed it up by the way), it was so rich it was like an old steam loco! I leaned the mixture off inside the AFM after speaking to Dom at Powers Performance who originally set them up from new.
Symptoms are :-
1. Test's lean on MOT Test Emissions machine and tests lean on Gunsons Gas-tester at home.
2. Plugs are thick black sooty, Tailpipe is thick black sooty (indication it's rich)?
3. Absolutely stinks (I mean really bad like tear gas - it's so acrid that it chokes you) when running, it's so bad the neighbours up to two houses up and down the road close the windows when it's running in the drive and you have to go and have a shower after you have put it in the garage (Indicating its rich).
4. Will start first turn of the key but you have to feather the throttle and keep the revs at about 1800rp until warm other wise it wont tick over (indicates its lean)?
5.Used to run out of steam around 4000rpm where it would cough and splutter and backfire. The rising rate FPR helped with this (indicates it's lean)?
6. Idle mixture screw doesn't seem to do a vast amount to the mixture, I can manage to get it up to 1.2 co and that's about as far as it will go.
I have done a leaktest and the head gaskets are OK as far as that will tell me (I thought maybe if they were tin gaskets and it hadn't ran for years it maybe them but no). Compression tests are as I have posted and the breather system seems fine.
I have the opportunity to borrow/buy someone's 390se ecu and afm next week as I can only think it's an ecu fault.
I am open to any suggestions from you guys as I am ready to push it off a cliff at present.
Jase.
Thanks for the replies guys,
I don't think its the temperature sensor but I will check it again. I think I replaced it to rule it out and have checked it since (but I will double check as it's been a while).
I have run it without the air filter connected before but no difference I am afraid.
I am pretty sure it isnt an air leak as I have tested for these in the past and resealed everything I can possibly think of including going all over the breather system.
I will try the ecu swap with another known good unit later this week and let you know my findings :-)
Jase.
I don't think its the temperature sensor but I will check it again. I think I replaced it to rule it out and have checked it since (but I will double check as it's been a while).
I have run it without the air filter connected before but no difference I am afraid.
I am pretty sure it isnt an air leak as I have tested for these in the past and resealed everything I can possibly think of including going all over the breather system.
I will try the ecu swap with another known good unit later this week and let you know my findings :-)
Jase.
It's not running rich, it's running weak.
The acrid smell is the poorly burnt mixture from a weak mixture misfire, your HC content will be sky high.
Rich mixtures burn well, weak mixtures burn poorly.
Follow the evidence .. you have 2 machines showing weak mixture yet you appear to have completely ignored them.
Sort the obvious faults first (ie get it running richer) and then report back.
The acrid smell is the poorly burnt mixture from a weak mixture misfire, your HC content will be sky high.
Rich mixtures burn well, weak mixtures burn poorly.
Follow the evidence .. you have 2 machines showing weak mixture yet you appear to have completely ignored them.
Sort the obvious faults first (ie get it running richer) and then report back.
Edited by spitfire4v8 on Sunday 8th August 15:04
That's an interesting fact I probably have the same issue with mine.
What was your hydrocarbon rating on the MoT tester then?
Adjust the CO for 1.0% and see if the acrid smell goes away.
Yes the CTS can fail at installation so best to check it again, measure the resistance cold and hot.
Other faults can be in the loom, so double-check readings for sensors at the ECU multiplug.
Has the ECU been re-flowed/re-soldered? Dry joints on the PCB can also cause running problems.
What was your hydrocarbon rating on the MoT tester then?
Adjust the CO for 1.0% and see if the acrid smell goes away.
Yes the CTS can fail at installation so best to check it again, measure the resistance cold and hot.
Other faults can be in the loom, so double-check readings for sensors at the ECU multiplug.
Has the ECU been re-flowed/re-soldered? Dry joints on the PCB can also cause running problems.
ECU was re-flowed by CES in 2005, maybe its gone dry again?
It wont run properly at all if I richen it up it belches black smoke out of the back.
I have had a look in the cylinders this afternoon with a borescope and they look like they are being washed clean which again would tell me that it's too rich would it not.
Jase.
It wont run properly at all if I richen it up it belches black smoke out of the back.
I have had a look in the cylinders this afternoon with a borescope and they look like they are being washed clean which again would tell me that it's too rich would it not.
Jase.
Rowley-Birkin said:
HC was 389 ppm (1200 ppm limit to passing the MOT)
CO was 1.14%
Doesn't make any sense does it
To be fair that doesn't make sense at all .. the evidence of poor running to the point it makes you choke does not compute with such low levels of CO and HC .. those are the values of a well running engine with no cats .. There is obviously more to this than meets the eye, apologies for suggesting you had not acted on the evidence, the evidence is conflicting.CO was 1.14%
Doesn't make any sense does it
No problem Spitfire4v8 - Yes that's why I am stumped, maybe I have found the earliest version of the emissions cheat device LOL!
I am going to try the "Borrowed" bits route and see how I go. I thought maybe mega squirt it if all else fails but I would like to keep it original if poss.
My thoughts are leaning towards the ecu, I will let you know how I get on.
Jase.
I am going to try the "Borrowed" bits route and see how I go. I thought maybe mega squirt it if all else fails but I would like to keep it original if poss.
My thoughts are leaning towards the ecu, I will let you know how I get on.
Jase.
If the plugs are sooted then it's rich some of the time. It could also be lean when readings have been taken at a certain rpm. Sooted plugs often occur at low rpm's which is usually when an inspection takes place. It's not so easy to check a plug at higher rpm's unless you go 'plug chopping'. If it reeks of fuel then it's rich.
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