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Old 08-26-07, 07:38 PM   #1
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Car sarts cold OK, but wont restart hot! Why?

My TII FC with 160,000 miles with clean & replaced vacuum hoses, radiator, harness, redone & flowed injectors starts great when cold but after a highway run, won't restart unless I pull fuel injector fuse, turn engine again for a few, then replace fuse. It starts again fine! SOmeone today told me that this is because of bad Apex seals. True? car still has power and does not smoke! Any idea? Sounds like a flooding issue, but when hot? Flooding usually happens when cold cars are not allowed to warm up. Thanks in advance!
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Old 08-26-07, 07:44 PM   #2
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umm, probably low compression with that mileage. Search. Many many threads on it. Exact symptoms.
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Old 08-27-07, 12:23 AM   #3
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lol everyones answer. "low compression"

read all of this and try it Looking for a car that has HOT START PROBLEMS

put a switch in to test it.
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Old 08-27-07, 02:57 AM   #4
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My car was like that but it was due to a coolent leak in my rear rotor. It could be low compression too. It will have more compression when cold because when it is hot the metal well expand making it has less compression.
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Old 08-27-07, 09:58 AM   #5
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water thermo sensor
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Old 08-27-07, 01:20 PM   #6
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replace water thermo sensor? install fuel cutoff? or do the mod on the above thread? don't know where to start!
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Old 08-27-07, 01:57 PM   #7
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do the mod i linked u to first. its wire and a switch, thats like 5$ of parts. switch on (pin 3b connected) when cold starting, switch off (pin 3b disconnected) when hot starting.

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My car was like that but it was due to a coolent leak in my rear rotor.
he said it doesnt smoke.

may be water thermo sensor too i suppose.
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Old 08-27-07, 02:35 PM   #8
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Quote:
Originally Posted by jrosado5 View Post
My TII FC with 160,000 miles with clean & replaced vacuum hoses, radiator, harness, redone & flowed injectors starts great when cold but after a highway run, won't restart unless I pull fuel injector fuse, turn engine again for a few, then replace fuse.
Its god punishing you for not using the search feature for such an easy and common problem.

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SOmeone today told me that this is because of bad Apex seals. True? car still has power and does not smoke! Any idea? Sounds like a flooding issue, but when hot?
"Somebody" is probably not worth talking to if he said "bad apex seals".. You probably have bad compression and an old engine... You can still have good power with poor compression...

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Flooding usually happens when cold cars are not allowed to warm up. Thanks in advance!
Uhm.. No. Flooding usually happens when the car is FLOODED... Say with FUEL..... I think thats why they call it flooding and not "My car is all warm-up-blue-balled".


Check your compression. If good, get injectors cleaned.
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Old 08-27-07, 04:49 PM   #9
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replace water thermo sensor? install fuel cutoff? or do the mod on the above thread? don't know where to start!
Water thermo sensor rarely fail. Just get your meter out and read the voltage on pin 2I. When the engine is HOT the reading will be b/t 0.4 and 0.5 vdc. If it reads that, then it isn't broken at all and or the wires did not fall off it.

If the water thermo sensor was broken or the plug off it, then COLD starting would be difficult. Why? Because the ECU defaults to 176* when that sensor is broken/off. That high a temp would result in a much smaller amount of fuel being delivered during START than would be with the sensor working right.

Frankly, 160,000 miles is a lot for a rotary engine and I wouldn't be surprised if the compression was not somewhat low. High milage RX bother me. I've seen worn out apex seals. At least a piston engine will knock or make some detectable noise prior to a piston going out/valve going out.

I'd either make a fuel cut switch or make a switch tied to pin 3B at the ECU. One or the other. The fuel cut switch is the least desirable of the two.

Or you could have a leaking injector. Which one? Got me. Mazdatrix makes a outfit that depressurizes the fuel rail when the engine is off. That is to keep the injector from dripping fuel into the rotor which causes flooding. There's cheaper ways to do what they sell for $$$$$$. A number 40 or smaller hole drilled in the fuel pump's outlet line will do the same thing and can be *undone* if the hole is too big or not wanted lated by simply putting a small hose clamp over the hole you drilled to stop it up.
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Old 08-28-07, 02:42 PM   #10
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Thanks Hailer! The injectors have been cleaned and flowed/charted, whatever u call it so the problem is the one you state. Easy on me Micaheli, I dont use this forum much until now! Thanks for your input anyway!
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Old 08-28-07, 03:19 PM   #11
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My 86 N/A would do that start great when cold and not start again when a normal temp. Found out I was leaking fuel from a Fuel line to the fuel injector rail. Fixed it and the car ran great again.
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Old 08-28-07, 03:35 PM   #12
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yeah the injectors are bitches on s4 cars, mine leaked and i replaced and upgraded with 720cc and a rtec7 1.8 upgrade. now it starts relibly w/ 130,XXX miles.
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Old 08-28-07, 03:45 PM   #13
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Quote:
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My 86 N/A would do that start great when cold and not start again when a normal temp. Found out I was leaking fuel from a Fuel line to the fuel injector rail. Fixed it and the car ran great again.
you were leaking fuel from the fuel line to the fuel injector rail?

HUH?
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Old 08-28-07, 04:02 PM   #14
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Quote:
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Thanks Hailer! The injectors have been cleaned and flowed/charted, whatever u call it so the problem is the one you state. Easy on me Micaheli, I dont use this forum much until now! Thanks for your input anyway!
Eh.. don't mind me.. I'm just cranky because I'm at work........... I have a feeling its the same reason RETed is such an ***. He must have a shittier job than me... lol
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Old 08-28-07, 04:14 PM   #15
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Yeah to my rail after I fixed it no more bad hot starts.
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Old 08-29-07, 09:48 AM   #16
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You would think if u had a fuel leak your car would of burned up by now!
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Old 08-29-07, 10:07 AM   #17
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Weak compression. An engine can still cold start and make good power going down the road but be on the weak end of compression. The threshold for HOT START FLOODING is around 95-90psi, there or less and the engine starts having issues. Rotary engines LOSE A LITTLE BIT OF COMPRESSION ONCE WARM...this is why they will start fine cold but not restart hot. Maybe you have 100psi on cold start, but only 95 on hot start. Also, on cold start, you have the benefit of OMP line drainoff and oil control ring drainoff, a puddle of oil in the bottom of the chamber that sloshes around and wets the apex seals, raising compression temporarily, but of course it burns off once the engine is started.

Cleaning injectors only helps if they were leaky to begin with.

A fuel pump cutoff switch, or better yet an injector delay/cutoff circuit, work to relieve flooding at hot start by giving the marginal compression time to increase with multiple rotations before you shoot in fuel.

From the factory, the engine made 120-125psi compression, and a significant amount of that compression was available within 1 rotation. Therefore mazda injected the fuel pretty much immediately. As the engine has worn out, *cranking compression* has gotten weaker also, thus you get more flooding. If you delay fuel injection long enough for cranking compression to rise after a few revolutions, then you can usually get around the low cranking compression issue.
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Old 08-29-07, 10:07 AM
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