94 MX-3 BackFire/Pop via intake

[Pheesh123]

Hey guys. Would like to ask you all a question. A week or so ago I was driving on the freeway and all the sudden my car started to bog, decelerate, even when i floored the accelerator my car simply bogged. I took it to a shop and they told me that my (rear) cat was clogged and that I should have it replaced. Once i replaced the cat, the muffler shop told me that a clogged/melted cat can be from bad spark and fuel mixture. Later that night a friend and I replaced the distributor cap, rotor, plugs and wires, and still having issues.

With the car in gear I struggles to pass 1.5-2k RPMS and if and when it does it is fine, this also causes a problem because I cannot get enough speed to shift so driving it around is a hassle.

Also, my friend and I discovered that when i give it alot of gas, and it bogs and sputters there is a loud pop that comes from the intake. the exhaust smells horrible as well.

I have read around the site some and there are posts about timing, fuel injector valves, fuel filters, pumps....


Any kinda of insight would be great guys, thanks for your time.

[Ryan]

could very well be your timing belt is taking a hike/jumped. Do you know when it was last replaced?

Do you need tips on diagnosing?

Any pre-existing conditions?

check for intake leaks using some sort of flammable spray around the intake tubes.

[Pheesh123]

Hey thanks for the reply! I appreciate it.


The timing belt has never been changed to my knowledge. Have had the car for at least 2 years, and the previous owner doesnt know when the timing belt (or any maintenance was done).


Any help you have diagnosing the problem will help. There is no pre-existing conditions that would add or effect the car this way. (oil drip, need of half axels, etc)


thanks again for your help

[Ryan]

I must say, I have never heard of this problem before.


Seen stuff go wrong on dyno's with NOS, but not just on the stock motor.

Is it for every cycle, or just occasional?

Any engine codes?

I would suggest a tune up anyway, since no one knows when it was last done. oil fuel and air filters, plugs, wires if they need it, disty cap and rotor, maybe belts if they need it. Maybe as deep as timing belt waterpump.

[Pheesh123]

I must say, I have never heard of this problem before.


Seen stuff go wrong on dyno's with NOS, but not just on the stock motor.

Is it for every cycle, or just occasional?

Any engine codes?

I would suggest a tune up anyway, since no one knows when it was last done. oil fuel and air filters, plugs, wires if they need it, disty cap and rotor, maybe belts if they need it. Maybe as deep as timing belt waterpump.

you asked every cycle, or just occasional? every cycle of the engine or occasional? I will most likely take a vid and post that here so you can see first hand what it is doing.

There are no check engine lights on the dash that come on, the car isnt notifying us of any problems.


we did an oil change a few months ago, prolly needs it again but dont think this is an oil problem. lol.

Fuel filter (hasnt been changed)
Need new air filter (we cracked open the air box to hear the popping noise better and it was filthy)

we changed the plugs (looked a little burned out)
dist cap, and rotor had ton or wear
and wires had corrosion on them. those are all new.

All belts are new, Alternator was changed out, and so we slapped new belts on there.

everything except the spark plugs,wire,cap,and rotor were changed months before this problem.


I will look into replacing some of this stuff like the other filters, and look into pricing of pumps, and stuff. I may invest in some dynamite and call it a day lol

[Ryan]

A BP will be less than a case of dynamite

I'd wait on some other opinions before digging too deep in, I'm not really sure what this is.

oh, and yeah, thats what I meant by cycle.

vid would be good

[Pheesh123]

43 seconds of stutter stutter put put.


http://www.youtube.com/watch?v=suAtNlt1RgI" onclick="window.open(this.href);return false;

[Limegreen mx-3]

have u check ur vaf/maf box I forget which term goes to which one.. don't know what i mean ur metal air meter flopper check if the connector connected snog.

[Ryan]

They're all VAF's.


That sounds like a fuel problem to me....

Its very odd.

Have you verified that the flow/pressure is good?

[Pheesh123]

They're all VAF's.


That sounds like a fuel problem to me....

Its very odd.

Have you verified that the flow/pressure is good?

No i have not verified flow and pressure, how do i go about doing this to the fuel system, there is a fuel system treatment (lucas) in the tank right now its just not really safe to drive around because sometimes you can get up into second gear because it chokes and sputters like you saw at around 2k...so the fastest I can get it up to is 10-15 mph at the most.

IF there are some simple fuel system checks that you can have me try out and relay the results to you guys lol

[Pheesh123]

have u check ur vaf/maf box I forget which term goes to which one.. don't know what i mean ur metal air meter flopper check if the connector connected snog.

sorry, i dont understand what you are getting at. want me to check the VAF sensors and if they are connected snug?...


If that is what ya mean, ill go look into it and report back.

thx for your input

[Ryan]

Well, Since I doubt you have (or access to) the proper guage, the best thing you can do is just remove the high pressure side fuel hose from the fuel rail (filter side) and then run the pump and make sure its a nice healthy stream coming out of there. Any resemblence to a dribble, and you've got problems.


Also, are all your plug wires on correctly?

[Pheesh123]

yes the plug wires are on correctly, we changed the plugs and wires etc after this problem was already here. I can only assume that they are on correctly, since the problem didnt get any better or worse with the change out. we followed the manual as well as the numbers on the dist cap. they all seem to be firing in time...


ill take a look at the fuel lines when i get home from campus today.

thanks

[Pheesh123]

interesting find...it may or may not have any bearing but I dont have the know-how to interpret what it means.

I took a timing light hooked it up to plug 1:
at idle it is firing nicely. when revved up, it speeds up, as expected BUT at the 1.5-2k RPM it stops firing, or fires 1-2 times for ever half second or so.

Hooked it up to plugs 2-4:
same thing, idling nicely, speeds up, but when you hit the magical RPMS they all but stop firing or fire at half the speed they should be.


checked the 2 plugs on the distributor that aren't plug wires and these fire extremely fast, both when revved speed up to nearly a constant beam of light.

was told to do this by my buddy he suspected that it was either fuel or spark, he was leaning more towards spark, does this mean any thing to you guys other than shelling out the cash for a new distributor?....anyone have one laying around their garage locally that they could chuck my way, I could swap on and see if it is the dist?


thanks, i can take another video of the light under idle,rev,and backfire, on plugs 1-4 if ya like...



also as an aside, the exhaust tips on the mx-3 are dirty as hell!....i mean jet black, as it was warming up black water was being sprayed out as i revved it. do these things go to say anything about the fuel, spark, problem i am having?

[Ryan]

I don't quite understand what you're saying.

on all cylinders they stop firing/fire incorrectly at that range?

What two plugs on the disty that aren't plug wires?


Maybe you do need a new distributor, since you already did cap and rotor


This is the DOHC 1.6? I'm sure someone has a dist lying around for you.