need guru on why we have hotstart foodings
12-06-04, 11:08 AM
#1
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need guru on why we have hotstart foodings
i realy want to now the reason why many rx7 owners have hotstart problem, i want detail explanation on this, it is so anoying . i dont want the switch fix , i want to now if somthig went bad , because when you buy your rx7 new its very rare this happens ,if anybody has figured it out, any mazda techs , please help every , on the forum lets make , this page big,so we all can get an idea where to start.
12-06-04, 11:21 AM
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1) The ECU has an agressive fuel feed when starting.
2) Rotary engines with high mileage & worn or cracked seals don't build quite as much compression as they used to when cranking.
3) Batteries & connections start to weaken over time.
4) Fuel injectors get clogged or stuck over time.
The oil film in the chambers is necessary to seal.
Any flooding will start wash out the oil.
2) Rotary engines with high mileage & worn or cracked seals don't build quite as much compression as they used to when cranking.
3) Batteries & connections start to weaken over time.
4) Fuel injectors get clogged or stuck over time.
The oil film in the chambers is necessary to seal.
Any flooding will start wash out the oil.
12-06-04, 12:34 PM
#5
First and foremost, compression has dropped on older original engines. Yes, it's still within acceptable limits per the FSM, but the lower your compression, the greater your chances of flooding consistently.
As discussed in a thread above, rotaries actually make more compression when cold than when warm, according to my evidence of testing many engines. This is why we dont often have cold start problems, but do when hot. The engine loses 5-15psi when warm, which may be enough to drop you into the threshold of flooding (around/below 95psi as best I can tell).
Also, the rotary builds cranking compression slower than a piston engine might, especially as compression drops over time. It might take a rotary 2-3 full rotations to build acceptable compression for combustion, compounding the flood issue. This is why a fuelpump switch or injector delay helps greatly in preventing flooding on an older engine, it gives the engine a few rotations to spin up and build cranking compression. This is also why rolling off a flooded engine always starts it, because the compression is higher with higher rpms.
Other things to look at are injectors, rail pressure, vacuum leaks, battery and starter strength and voltage/connections.
As discussed in a thread above, rotaries actually make more compression when cold than when warm, according to my evidence of testing many engines. This is why we dont often have cold start problems, but do when hot. The engine loses 5-15psi when warm, which may be enough to drop you into the threshold of flooding (around/below 95psi as best I can tell).
Also, the rotary builds cranking compression slower than a piston engine might, especially as compression drops over time. It might take a rotary 2-3 full rotations to build acceptable compression for combustion, compounding the flood issue. This is why a fuelpump switch or injector delay helps greatly in preventing flooding on an older engine, it gives the engine a few rotations to spin up and build cranking compression. This is also why rolling off a flooded engine always starts it, because the compression is higher with higher rpms.
Other things to look at are injectors, rail pressure, vacuum leaks, battery and starter strength and voltage/connections.
12-06-04, 12:56 PM
#6
Originally Posted by dennis blackstone
i realy want to now the reason why many rx7 owners have hotstart problem, i want detail explanation on this, it is so anoying . i dont want the switch fix , i want to now if somthig went bad , because when you buy your rx7 new its very rare this happens ,if anybody has figured it out, any mazda techs , please help every , on the forum lets make , this page big,so we all can get an idea where to start.
We know that a significant amount of fuel needs to enter the chamber to result in flooding and washing away the small amout of oil on the walls. Now, this fuel enters through leaking injectors, an engine cranking too slowly and not be able to keep chamber clean, or the ecu see a cold start and "dumps" more fuel than is needed into the engine flooding the plugs.
I bought a '88 TII new then a '89 TII which I still have. I personally have never encountered the flooding after shut down. The only problem I've ever had was when the car would sit for 2/3 months in the cold garage, no compression on startup. Springs were probably weak in the original engine and therefore not enough pressure was exerted on the seals to keep in contact with the housing. So it was really low compression which caused a no start problem, not flooding.
One I got it started, it would run fine until the following year. I had to be sure and start it every couple of weeks then fine.
12-06-04, 01:18 PM
#7
I think the bulk of it can be traced to "really, really stupid ECU." It's philosophy seems to be along the lines of "When in doubt, add more fuel."
If you have a late enough ECU (I think 88.5 or beyond) you can cut off the injectors by flooring the gas pedal while cranking. This is the same thing as a fuel cut switch, just built in.
Alternately, you can fix pretty much all the problems (starting, rich running, etc) by going to a well tuned standalone.
I don't see a problem with a fuel pump cut switch. Yes, it's a "quick fix", but it works reliably, is cheap, and if moderately hidden serves as an extra security device (since the door locks are basically useless for keeping people out). The only thing to watch out for is that if you have a turbo, make damn sure the switch can't be hit while you're running - the fuel pump cutting out under boost will lead to a temporary lean condition before the engine stops - boom. Same thing with a NA, but it's not quite as critical.
-=Russ=-
If you have a late enough ECU (I think 88.5 or beyond) you can cut off the injectors by flooring the gas pedal while cranking. This is the same thing as a fuel cut switch, just built in.
Alternately, you can fix pretty much all the problems (starting, rich running, etc) by going to a well tuned standalone.
I don't see a problem with a fuel pump cut switch. Yes, it's a "quick fix", but it works reliably, is cheap, and if moderately hidden serves as an extra security device (since the door locks are basically useless for keeping people out). The only thing to watch out for is that if you have a turbo, make damn sure the switch can't be hit while you're running - the fuel pump cutting out under boost will lead to a temporary lean condition before the engine stops - boom. Same thing with a NA, but it's not quite as critical.
-=Russ=-
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12-06-04, 01:21 PM
#8
I've heard of some cars being fitted with a "cranking sensor" device - if the engine has been cranking for more than 3 seconds (or something like that), it cuts off the injectors (or fuel pump, not sure) until the key is released. I should look into building those.
-=Russ=-
-=Russ=-
12-07-04, 10:51 AM
#9
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Originally Posted by dennis blackstone
i realy want to now the reason why many rx7 owners have hotstart problem, i want detail explanation on this, it is so anoying . i dont want the switch fix , i want to now if somthig went bad , because when you buy your rx7 new its very rare this happens ,if anybody has figured it out, any mazda techs , please help every , on the forum lets make , this page big,so we all can get an idea where to start.
12-07-04, 11:16 AM
#11
Originally Posted by dennis blackstone
we need experts ,mazda dealer techs rotery shops, to put their input, so we can get to the bottom of this.
What more can you ask for, Kevin gave you a reply and I'm he has a great deal more experience than a Mazda tech, esp. on rotaries.
12-07-04, 11:45 AM
#13
we need experts ,mazda dealer techs rotery shops, to put their input, so we can get to the bottom of this.
First, the "experts" will usually be independent shop owners, and there are a few enthusiasts here and there with that amount of knowledge. Second, dealer techs usually know as much about rotaries as you and I know about the space shuttle...we know what it looks like and how it works to some degree, but have never laid hands on it, much less know the theories behind it's operation. And finally, if the answer I posted above isn't good enough for you, you're going to be disappointed with the other responses you find on this forum.
Kevin Landers <---- rotary engine builder and shop owner, NOT dealer tech, and apparently not smart enough for this guy...
12-07-04, 02:34 PM
#15
Don't expect any tech with "MAZDA" on his/her shirt to know ANYTHING about rotaries or their little quirks. I work on my own rotary cars because whenever I start to talk rotary engines with any tech, mazda or otherwize, in minnesota i get blank stares and generaly ostricized.
12-08-04, 09:53 AM
#16
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I must agree that Kevin Landers knows as much about the problem as anyone. I have wasted so much time in diagnosising a hot no start problem. I used the value from the factory service manual that 85 psi was the aceptable minimium. My new RA seals gave me 95 in the front and 100 in the rear. The car will not start. Landers speaks of these values as being around the threshold of no start and he's right. If I oil the rotors the engine will start every time. As aside I hope the RA seals will wear in? Although if they are so hard I wonder what will wear what.
12-10-04, 01:55 AM
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The ECU runs very rich on starting so anything that could affect the
AFR could be a contributor. When cranking, the ECU decides how
much fuel to inject on the basis of the water temp sensor (the AFM
is ignored). There is one additional correction for battery voltage
(to compensate for injector opening response time).
My theory on why its frequent on short starts is that the rotors/chambers
warm up a bit but the coolant does not. Attempt to start again, and the
ECU still thinks its a stone cold engine but less fuel condenses on the
walls of the chambers and the mixture is now too rich -> flood.
Other potential contributors:
- bad FPR
- bad BAC or driver to BAC (I've experienced this one)
- leaking injectors
- low compression
- worn injectors, that now open faster or flow more than when new
- bad coolant temp sensor
likely it takes more than one to cause continual flooding issues. BTW its
not just rotaries that flood, my buddies brand new BMW flooded on him
in the first couple of months he had it (moved it to wash it, flooded on
starting after the wash, engine was not washed/wet).
-Henrik
AFR could be a contributor. When cranking, the ECU decides how
much fuel to inject on the basis of the water temp sensor (the AFM
is ignored). There is one additional correction for battery voltage
(to compensate for injector opening response time).
My theory on why its frequent on short starts is that the rotors/chambers
warm up a bit but the coolant does not. Attempt to start again, and the
ECU still thinks its a stone cold engine but less fuel condenses on the
walls of the chambers and the mixture is now too rich -> flood.
Other potential contributors:
- bad FPR
- bad BAC or driver to BAC (I've experienced this one)
- leaking injectors
- low compression
- worn injectors, that now open faster or flow more than when new
- bad coolant temp sensor
likely it takes more than one to cause continual flooding issues. BTW its
not just rotaries that flood, my buddies brand new BMW flooded on him
in the first couple of months he had it (moved it to wash it, flooded on
starting after the wash, engine was not washed/wet).
-Henrik
12-10-04, 02:12 AM
#18
Ecu this, ecu that. True, the thing is slow, archaic, and not adaptable to new conditions at all. But you know what? It worked well enough when the car was new, and has continued to do so for (in most cases) 100k miles or more. Correct me if I'm wrong, but the programming and values of the ecu do not change over time. Injector properties do change a small amount, but not to the extent that some would have you believe.
BUt, we've been at a point the last 5 years or so (on fc's) where most of the cars are on original engines with 125k or more miles. In most cases, around this point, compression has dropped about 30% from new. That is plenty enough to cause problems. Since compression is heavily dependent on rpm (especially as seals and springs are worn more and more) it's easy to see why startup is the main point for a problem to spring up.
After years of testing with literally hundreds of cars and engines, and swapping parts, doing electrical testing, i've come to the conclusion that compression is the single biggest factor here. I've taken engines that flooded, rebuilt them, installed all the original wiring and injectors back onto them, and mysteriously after breakin is complete and compression raises up, flooding stops, never to return (at least for several ten-thousand miles, anyway) . I've taken injectors off of engines that didnt flood, and put them onto engines that did flood, and the engines still flooded. I've taken injectors off of engines that did flood, and put them onto engines that did not flood, and they still did not flood. Same for computers. And coils. And fuel pumps. And rails with regulators. I've run tens of engines with no emissions and air injection controls whatsoever and provided compression is up to par, never experienced flooding due to lack of a proper bac or other controls. I've run larger injectors on untuned ecu's with heavily ported engines, you name it, and provided I made good compression, rarely had a problem flooding. All the evidence points to one thing.
True, you can MAKE a great engine flood by doing one of the things listed above, but you wont have consistent problems without low compression.
BUt, we've been at a point the last 5 years or so (on fc's) where most of the cars are on original engines with 125k or more miles. In most cases, around this point, compression has dropped about 30% from new. That is plenty enough to cause problems. Since compression is heavily dependent on rpm (especially as seals and springs are worn more and more) it's easy to see why startup is the main point for a problem to spring up.
After years of testing with literally hundreds of cars and engines, and swapping parts, doing electrical testing, i've come to the conclusion that compression is the single biggest factor here. I've taken engines that flooded, rebuilt them, installed all the original wiring and injectors back onto them, and mysteriously after breakin is complete and compression raises up, flooding stops, never to return (at least for several ten-thousand miles, anyway) . I've taken injectors off of engines that didnt flood, and put them onto engines that did flood, and the engines still flooded. I've taken injectors off of engines that did flood, and put them onto engines that did not flood, and they still did not flood. Same for computers. And coils. And fuel pumps. And rails with regulators. I've run tens of engines with no emissions and air injection controls whatsoever and provided compression is up to par, never experienced flooding due to lack of a proper bac or other controls. I've run larger injectors on untuned ecu's with heavily ported engines, you name it, and provided I made good compression, rarely had a problem flooding. All the evidence points to one thing.
True, you can MAKE a great engine flood by doing one of the things listed above, but you wont have consistent problems without low compression.
12-10-04, 02:19 AM
#19
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I concur - compression is culprit #1.
If it was anything else, why does a "fresh" rebuild solves this flooding problem 99% of the time?
If it was the ECU, then the rebuild would do no good.
A rotary engine quick loses compression as compared to a piston engine; this is why you don't typically hear of flooding problems from pistons engines due to dropping compression.
I think electrical system condition is #2.
Corroded battery terminals, dying starters, dying batteries, crappy alternators, with crappy grounds cause for crappy cranking conditions.
-Ted
If it was anything else, why does a "fresh" rebuild solves this flooding problem 99% of the time?
If it was the ECU, then the rebuild would do no good.
A rotary engine quick loses compression as compared to a piston engine; this is why you don't typically hear of flooding problems from pistons engines due to dropping compression.
I think electrical system condition is #2.
Corroded battery terminals, dying starters, dying batteries, crappy alternators, with crappy grounds cause for crappy cranking conditions.
-Ted
12-10-04, 07:10 AM
#20
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Originally Posted by SureShot
1) The ECU has an agressive fuel feed when starting.
2) Rotary engines with high mileage & worn or cracked seals don't build quite as much compression as they used to when cranking.
3) Batteries & connections start to weaken over time.
4) Fuel injectors get clogged or stuck over time.
The oil film in the chambers is necessary to seal.
Any flooding will start wash out the oil and reduce compression further.
2) Rotary engines with high mileage & worn or cracked seals don't build quite as much compression as they used to when cranking.
3) Batteries & connections start to weaken over time.
4) Fuel injectors get clogged or stuck over time.
The oil film in the chambers is necessary to seal.
Any flooding will start wash out the oil and reduce compression further.
I'll revise my list:
1) Rotary engines with high mileage & worn or cracked seals don't build as much compression as they used to when cranking.
2) The ECU has an agressive fuel feed when starting.
3) Batteries & connections start to weaken over time.
4) Fuel injectors get clogged or stuck over time.
12-10-04, 07:54 AM
#21
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^ agreed completely
but it sounds like even good compression engines are having problems with this (renesis).
im still thinking the over fueling issue needs to be addressed somehow, i wish i had a s5 so i could just hold the throttle all the way open to cut the injectors off, ( i think the rtek chip adds this feature to s4). But if you have a s4 with good compression, and good crank, spark and all that stuff and still run into flooding, a fuel pump cut off switch is about your only option...right?
but it sounds like even good compression engines are having problems with this (renesis).
im still thinking the over fueling issue needs to be addressed somehow, i wish i had a s5 so i could just hold the throttle all the way open to cut the injectors off, ( i think the rtek chip adds this feature to s4). But if you have a s4 with good compression, and good crank, spark and all that stuff and still run into flooding, a fuel pump cut off switch is about your only option...right?
12-10-04, 08:34 AM
#22
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Can someone explain this to me:
When engine is hot and you are about to start it, the FPR Solenoid vents the FPR (to atmos pressure). This means the fuel pressure at the rail is maximum (for NA models, 86-88).
Why would you want to raise the fuel pressure when trying to start a hot engine ?
hugues-
When engine is hot and you are about to start it, the FPR Solenoid vents the FPR (to atmos pressure). This means the fuel pressure at the rail is maximum (for NA models, 86-88).
Why would you want to raise the fuel pressure when trying to start a hot engine ?
hugues-
Last edited by hugues; 12-10-04 at 08:36 AM.
12-10-04, 09:11 AM
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Originally Posted by hugues
Can someone explain this to me:
When engine is hot and you are about to start it, the FPR Solenoid vents the FPR (to atmos pressure). This means the fuel pressure at the rail is maximum (for NA models, 86-88).
Why would you want to raise the fuel pressure when trying to start a hot engine ?
hugues-
When engine is hot and you are about to start it, the FPR Solenoid vents the FPR (to atmos pressure). This means the fuel pressure at the rail is maximum (for NA models, 86-88).
Why would you want to raise the fuel pressure when trying to start a hot engine ?
hugues-
12-10-04, 07:50 PM
#24
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Originally Posted by hugues
Can someone explain this to me:
When engine is hot and you are about to start it, the FPR Solenoid vents the FPR (to atmos pressure). This means the fuel pressure at the rail is maximum (for NA models, 86-88).
Why would you want to raise the fuel pressure when trying to start a hot engine ?
When engine is hot and you are about to start it, the FPR Solenoid vents the FPR (to atmos pressure). This means the fuel pressure at the rail is maximum (for NA models, 86-88).
Why would you want to raise the fuel pressure when trying to start a hot engine ?
Now, the question is whether this really works or causes more headaches?
-Ted
