Hi all,
I have read around and I know what usually causes these sorts of problems, but will post anyway since I have tried to fix everything and I'm stumped.

When starting stone cold, it has NEVER done so before, but it struggles to start, slowly rises to 1500rpm and an assload of smoke pours out my exhaust, looks and smells like fuel smoke (REEKS of fuel).

When hot, never done so before either, I turn the key to start and it feels like the engine thinks it's already started, the tacho bounces while starting, then once started (usually 2 or 3 turns of the engine) it slowly comes up.

In either case, if I hit the accelerator while it's slowly coming up, it jumps straight up to idle speed (mine has always idled at 1500rpm, don't know why, tried everything to fix, but that's just the way it wants to work) and runs perfectly.

I haven't compression tested since I've been at work all day, but pulled the plugs and while cranking can hear the distinct puffs coming from the engine, none sound weak they all sound exactly the same, did smell a LOT of fuel though.

I'm guessing I have either a fuel and/or throttle problem. Just wondering if someone can help out here. I'm definitely flooding on shutdown by the looks of things but I'm unsure as to whether it's a fuel or throttle side issue. My thoughts:

Throttle stuck open a bit, will get in there and grease up my throttle cable though I've looked at it before and never seemed to have a problem. This would explain the engine flooding on shutdown and then a bucketload of smoke on starting up as it's burning off the excess fuel in the engine.

AFM bad?
TPS bad?
ECU bad?
Injectors dirty/bad?
Vac line blown off somewhere?
Pulsation damper bad?
BAC valve bad?
Bad turbo? Though this would be oil smoke presumably not fuel as it appears to be.

I'm really stumped. I should mention however that once the excess fuel smoke comes out, which usually takes about 10-15 seconds, the car produces NO smoke at all, and yes I have tried revving the engine to about 5000rpm and immediately letting go, nothing.

Also I have taken the rad cap off and run it, there is no bubbles, and the engine smelled of fuel when the sparks were out, and they seemed to have a bit on there as well. No smell of coolant at all. So I do not suspect a blown engine at all.

Really hoping here that it's not a blown engine because I really can't afford that right now. I don't presume it is though because surely the engine wouldn't run perfectly after the accelerator is depressed at all or once it's burned off what appears to be excess fuel?

Specs:
Series 4
69,746km
3" Exhaust
FCD
Everything else stock

Thanks for the help and sorry for the long post,
Sean

 

I have just about the same issue as you do! Although I have a series 5 NA with 85k miles, a 3 inch exhaust and a k&n dropin. If anyone has an idea please chime in.

 

Sounds to me like your injectors are leaking and causing it to not only flood but fouls your plugs a bit too. Unless you pull the EGR fuse when you're cranking the motor over with the plugs out, the inejctors are still going to inject fuel into the housings . This can get dangerous.

Try something just to humor me; with the engine idling, disconnect the fuel pump at the back of the car underneath the carpet. Let the engine suck up all the fuel and die. Let it all cool down overnight, reconnect the pump and see If it makes any difference in the starting behavior. If it does, congrats, you need to send your injectors off to witch hunter for cleaning. Inexpensive and awesome.

 

you have a series five car. Try keeping the throttle floored while you start it. Built-in fuel cut.

 

I thought this might be the case but wasn't 100% sure. I'll do that tommorow when I don't need to get to work the next day. lol. I'd say it is leaking injectors though, would make sense, wasn't sure if they would just require cleaning or whether they were actually stuffed. Also with these cars Occam's Razor never usually applies.

Isn't disconnecting the fuel pump going to cause detonation and therefore not be particularly good for my engine though? Might just be worth getting the injectors sent off for cleaning regardless and giving that a shot. It's due for a service in a few weeks anyway, might just take it to a mechanic instead of doing it myself and have him send the injectors off while it's there.

Thanks for the help,
Sean

 

Just disconnect the fuel pump while it's idling, let it completely cool off and try starting it. Seriously, just do it.

Removing your injectors isn't hard at all. Gotta go thru the intercooler and remove the TB/UIM. Easy as pie, takes maybe an hour.

 

I always do things the old fashion way..

fuel pressure gauge. test spark voltage, And i also check to see if the injectors are fireing.

Might also help to have a Air fuel mixture gauge too. Ill tell you with these cars it could be any number of things. But one thing i did do was install a switch in the car so i can turn off the fuel pump when i want. That tells me ALOT when i switch it off when its running. If it shuts off right away you could have low pressure..

It should stay running for close to three seconds after you shut the fuel pump off.

 

It should stay running longer than that. More like ten seconds.

The old fashioned way takes longer than a very very simple test to rule out leaking injectors, which is a very common problem. If the problem persists, yes, go out and get a fuel pressure gauge and follow the FSM and it's troubleshooting list.

I'm not shooting you down or anything man, I'm just trying to help him get the basic out of the way quickly and easily before he has to further tear into it like I did.

BTW, there is what's called the water thermo switch on the back of the coolant filler neck...it has a green plug on it. It's common for one or both female spades inside the plug to push back some losing contact with the sensor...it can very well cause cold starting issues.

Also, obviously, are your plugs in good shape? Old or worn plugs don't help matters.

Even if you don't want to spend the $80something on having your injectors repaired, you should just for good measure, whether it's the problem or not. While you're in there, replace any fuel or vacuum lines around and about...this will rule out future issues and keep you running smoothly. Why tear into it more than once? Eliminate the pulsation dampener...seriously...get rid of it.

 

+1 I think its also the leaking injectors. i also had this problem on my s4 tii and i just sent mine in to get cleaned and flow tested, put it back in and fixed my problem. But also, with these old cars, you mite want to check the fuel pump wiring, to see if they are in good shape. I would look into doing a fuel pump rewire. Also when you take off the injectors, becareful on the primary one's, there is a little spacer(black) thats goes inbetween the fuel rail and engine block, so when you unscrew it, make sure you don't lose that. you'll just mess up the injectors again if you put it back on without the spacer.

 

The injectors are definitely firing, too much in fact since my fuel usage is absolutely horrendous.

Spark plugs are brand new from 400km (2 months) ago NGK BR9EQ and BR7EQ plugs. So no way they're causing the problem.

Replacing vac lines anyway, I have a long weekend coming to me so I'll probably tear into it then and try to get the whole lot done. Still trying to track down somewhere with 3.5mm silicone hose to do it though.

Will disconnect the fuel pump while running to check leaking injectors, if that is the problem it's intermittent, this afternoon when I left work car started as normal, at lunchtime when I was inside for about half an hour and went back to it so it was reasonably hot it wouldn't start at all and had to pull the EGI fuse, crank to remove fuel then put it back in, started perfect and went back to work. Yet yesterday when it was cold it was hard to start, so definitely suspecting injectors.

Is it possible FPR could be causing an issue?

I'll also try and track down the instructions for deleting the pulsation damper, I've heard it's bad, I don't fully understand wtf Mazda was thinking using it in the first place since all it seems to do is cause problems.

Will also see if I can hack a switch into there for turning the pump off in case of future flooding.

Will get back to you on Sunday when I have a day off and get a chance to try shutting off the fuel pump while running. Was going to get the injectors cleaned anyway, so I'll make a point of doing that now.

Thanks,
Sean

 

Its kind of hard to tell if its the fpr, you need some kind of gauge to check if thats it. But if it isn't holding pressure, correct me if i'm wrong, i think i mite leak out the fuel. check to see if the voltage is good on the fuel pump and also you mite just want to check the fuel main relay while your at it just in case, that also mite be the problem, not opening and closing correctly. well, anyways, good luck!

 

Thanks for all of the replies to the original post. I figured that it may be the injectors due to the fact that there are no bubbles in my cooling system. I will do the injectors when I do my springs and shocks next month. Thanks again, i love this forum.

 

Sorry for dragging up an old thread but figured I'm better off doing that than starting another new one.

Still having the same issue, pump, injectors, FPR and all the fuel system have been ruled out (the injectors were dirty but have now been cleaned and have since had no problem with flooding, only happened once, wierd.) and the FPR/pump have been tested and flow is good.

I am now almost certain that the reason I am using so much fuel is because the cold start system is not disengaging properly. When I startup I can hear the car warm up and the cold start system disengage as the idle tries to drop, however the idle bounces instead, it's like the thermowax is forcing the TB open again to make it idle higher when it shouldn't be.

I am about 90% sure I can blame all issues on the cold start system, as I am unsure if someone can confirm but I am fairly sure the car uses more fuel on cold start to warm the car up quicker. I believe it is not disengaging at an ECU level therefore causing it to just use bucketloads of fuel.

Regardless of if I start with clutch depressed and in gear, it still appears to be trying to go into cold start mode. Is there some way of eliminating it at the ECU level short of an Rtek chip (which is no good to me since I'm on a series 4 ECU anyway)?

I have an O2 sensor here I am going to install hopefully later today once the car dries (just gave it a massive wash) and vacuum lines I need to install once I have the time (going to trade off the rubber lines for silicone, even though they look ok, figure it's a good reliability mod worth doing).

Can someone confirm which sensor tells the ECU to exit cold start mode? The one on the radiator or the one on the water pump? And if there's some way of just eliminating it from causing a problem.

Thanks,
Sean

 

https://www.rx7club.com/showthread.p...40#post9214040

Do what I did.