Hi everyone,
I been searching for a while now but not enough info for my problem.
It's about few months now, that my car started to detonate at low rpm's, especialy when cold, while warming up, if I just tap the gas pedal a litle it will detonate real loud.

Even when the car is fully warmed up and driving in traffic and I don't pass 2.5K to 3K rpm when slow shifting it will detonate a litle , never did that before.

I changed the dashpot thinking it may not work well, many of you know what dashpot is, defected one will allow the trotle to close to fast and detonation will acure, and nothing,
I changed the 02 sensor and I did comlete tune up (dealer parts) exept gas filter, visualy checked the vacum hoses, they seem OK, map sensor is ok, air/fuel ratio gauge shows perfect mixture more rich than lean when boosting.

I have noticed that if I rev the engine at the trotle body by pooling the cable and looking at the double trotle, dt. doesn't seem to move at all close or open, I removed the vacum hose from it and there is no sucktion at all, reving or not, so I may have vacum leak somewhere right?
Idling is just perfect as allways. Car works exelent and pulls like crazy but this detonating crap is realy pissing me the **** off.

My only mods are catback, downpipe and moded air box.

Thanks for reading, sorry for the long post,,,, any help will be highly appreciated.

GAZIVODA .

 

Ummmm, are you sure it's not popping from rich a/f? I really don't think the motor will still be running if it was det that much (all it takes is one). You'll also get error code from the ecu comming from the knock sensor.
Det sound comes from the engine, not the exhaust.

 

No error codes nor runing to reach, with my mods and stock ECU I should be starting to run lean and possible boost spikes. By next week I should be putting a Pettit racing ECU, will se what's gonna happen.
The det. sound comes from exhaust, loud exhaust pops, that comes from the engine right?

 

that's not detonation. that's normal.

most healthy fd's have a small little backfires...more like puttering at the exhaust. The ones without cats spew fire.



detonation would be heard from the engine bay, and in the cabin of the car.

 

If what you said a accurate, and that this started to happen without any mods been done, then it would be a good idea to check the plugs and wires (and O2 sensor).
The poping comes from unburned fuel igniting in the exhaust system, IF every thing remains the same then the only items effecting the combustion is what I just mentioned.

 

I did the the tune-up just 2K miles ago, OEM parts, changed the O2 sensor also with Bosch universal one nothing ever changed.

Do you think I should use some sort of different plugs, warmer or colder...

 

Any sugestions on spark plugs or anything else to prevent this backfiring

Thanks...

 

If you put in an aftermarket ECU, expect more backfiring - they add more fuel, which makes for more pops.

Check your plugs & plug wires to make sure they are good. Fouled plugs or the wrong type of plug wires can cause higher than normal amounts of unburnt fuel - which is what causes the backfiring. Get a good set of wires from RX7.com - I got the NKG set... my mechanic approved. May as well get new plugs from them while you're at it.

 

I usualy tune my car up every 8-10K miles and it allways rane great, but lately with that backfiring **** is like anything I do doesn't wanna improve, and it only happens in low rpm.

Do you guys experience the same problem as I do, constant backfiring or just once in a while?

So BrianK, you are sayng that when I upgrade the ECU it will actualy backfire even more?
Hmmmm, its freaking me out.

 

With an open exhaust, backfiring is normal, but only occasionally. It usually happens when you let go of the throttle quickly after close to wot. Normal light load driving shouldn't cause any backfiring.
After market reprogrammed ecu increases the injector duty cycle (providing more fuel), more fuel, more backfire. But you said you didn't do any mods before this started to happen, so it shouldn't be an issue.

 

if your engine was detonating that much, your engine would not be running right now! Back firing is normal. Could be that your injector is leaking or your acv went out. try to check those things. In anycase, dont worry; as the old saying goes... dont sweat the petty things and dont pet the sweaty things

 

does it sound something like... mmmmm.. pop pop.... mmmmmmm mm.. pop..mmmmmmm pop

if it does its MISFIRING. not back firing..
a back Fire is like WRAAAAAAAAAAAA POP!
check your plugs.. happend to me.. or the plug cables..
check the whole spark plug system

 

Well, mine did. Granted, it wasn't a huge increase in backfiring, but I did notice it a bit more - especially when lifting off in the upper revs.

You might try having your injectors rebuilt. it's not incredibly expensive (I think about $125 after they are pulled out). Might be possible that you're not getting a good spray, but more of a dump instead. If that were happening, you wouldn't get an even burn which may lead to more unburnt fuel heading out the pipe. (this is just a guess on my part, however, getting injectors rebuilt is a good thing to have done anyway - especially for a car with over 60K on the odometer). If you know how to pull them, you'll want to send them to RC Engineering.

Beyond that, it could be any number of things. How bad is it? How many pops? Does it continue doing it for the entire duration of your drive or does it calm down when the engine is warmed up?

When I did backfire, I never got more than about 4-5 pops at low rpm and usually not more than 2 in the upper rev range. I don't think I ever got a backfire until lift-off (in other words, never when the gas pedal was pushed).

 

Well the way it happens is that when warming up the engine if I just tap the gas pedal or wanna just move the car a litle before complete warm up when I let go the trotle while closing up it pops 3-4 times pop,pop,pop ... pretty loud to.
The other way of poping fully warmed up is, if I'm downshifting from lets just say from 3rd to 2nd (all happens in low rpm range between 2-3K rpm) and I just tap the gas pedal in between shifts for better shifting or even just for kix, fun sometimes I get 2 pops.
I noticed when I rev the engine up to 3k rpm by just taping the gas pedal it does pop, but if I rev more lets say to 5K rpm or more than that it doesn't pop at all, I guess it burns the gas good and doesn't leave any in exhaust to backfire.

 

good point Briank.....my buddy had a leaky injector and as a result he was getting poor gas mileage and lots of backfiring.

 

Not realy like that NiMor, Idling and reving is perfect no misfiring for shure, the pops are only when the trotle closes and in low rpm, it would sound like this: wrooom-pop-pop,,, wrooom-pop-pop,,, wrooom-pop-pop-pop.
And the cables and plugs are just 2k miles old, never got floded it allways starts on a dime, it did happen even before tune-up that's why I did the tune-up even before 8K miles.

My freaking digi cam is screewd up, I'd post the real sound... shiznee.

 

It makes alot of sense what BrianK and skunks are sayng bad injectors throwing to much gas and not sprayng right that may be the answer to my question, and I've noticed lately more poore gas mileage than before I think !!!

Well as far as mechanical skill I usualy do most of the work myself in my car (I dont like no one messing with my babe, one of my friends mechanic asked me where are spark plugs and how many cilinders it had,,, ironicaly I just left the shop), but when it comes to injectors I never removed them or got to that point yet.
How hard is to take em out?
How much are new injectors?

 

Any other sugestions ?

 

Definitely check your plugs, and hold off driving it until it's got the new ECU. Just from my experience.

 

what you're getting sounds pretty normal, however, like I said, rebuilding the injectors is a good idea.

I have no idea how much new ones cost.

looks like they're not in the easiest place to get to (under the UIM):

 

the only thing holding the uim on is 5 bolts, about 8 vaccum lines and 2 eletrical connectors!!! not that hard to take off, just lable everything you take off with numbers so you keep track of how many you have to put back on and dont drop anythingin the lim and your golden!!!

 

Working on the spark and fuel system might clean it up a bit but it sounds like its just adding fuel on decel insted of cutting it. I know how to adjust that on the Power PFC.... I dont know about the Pettit ECU though.

 

Thank you all so much for all the great help and sugestions.

I guess I'll just wait a lilte more till I get my **** together, hopefully I'm going to do the vacum hose job soon and nonseq. simplification and rebuild the turbos at the same time I guess I'll send the injectors for rebuild to CNC ing.

Is no biggi if drive a lilte more like this right? I don't thing it will do any engine damage...

Anyway one more time - Najlep¨e Hvala - (Thank you so much)

 

Removing UIM !!!! I hear alot of horor stories removing that crap, anyway nothing is inposible, I'll tear that socker off somehow.

Thank you for the pic...

 

Don't worry too much about the backfiring. You should hear my truck, although it does not spit fire, it sounds like a freaking gunshot when I let off of it. The information given is great info, and should help you out.

- Steiner