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Discussion Starter #1
as some of you may know, i have been having some problems with my car and the way it is running. i recently changed my spark plugs(champion 71) with a .35-.37 gap. now, i don't have problems starting the car anymore, but my backfires have gotten worse. whenever i am driving and let my foot off the gas(in gear) the car makes some nasty loud backfires, and my a/f ratio gauge goes all the way to lean and sometimes the last light isnt even there when i backfire. now my question is: why is it doing this?
do i need to regap my plugs? do i need to go ahead and install the fuel filter that i have?
this problem is getting really annoying. i want my car to run the way it is supposed to. btw, i also sometimes(erratic) have a problem with the car under WOT. when i go into wot in 2-4th gear, the car sometimes hesitates very abruptly. the boost stays where it normally is, but it feels as if the car just lost 80 hp.


sorry for the long post, but i am looking for answers so that i can get my car back up and running the way it is supposed to.


cheers,
 

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still could be your plugs.. I won't trust anything beside NGK's..

also.. when you take your foot off the gas, your A/F gauge shouldn't be working at all anyways.. so that's not something you should be worried off..
 

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Please post a list of mods and how your tuning the car. How much boost are you running? You may have to go smaller with the gap.

I am an engineer in the automotive industry and Champion has some of the best plugs and quality control in the industry. They are just as good if not better than NGK. Almost all plugs are made using the same equipment, the same processes, the same materials. There is VERY little difference in plugs, none of the manufacturers are reinventing the wheel here.

Search previous posts for more info.

BTW I run 20 psi of boost 550HP 11 second times with #71 Champions and no problems.
 

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Discussion Starter #4
the list....

well, my mods arent too hefty:
HKS dual mega flow, gutted precats, downpipe with stock cat(prob clogged, not sure), champion 71 plugs, ngk wires, RPS III clutch, fidanza flywheel. greddy bov, boost gauge, and a/f monitor, running 12lbs of boost.


not sure if it has any relevance, but i am using a k&N oil filter, and mobil 10-30 synthetic. and redline fluids throughout the tranny.

hope that helps.

cheers,
 

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I don't see how the plugs make much difference with backfire. However, if you have the throttle cable too tight, the throttle plate will slam closed too fast which can cause a rich mixture and backfire. Has happend to me after a plug change.

BTW, the A/F meters (O2 sensors) are ALWAYS working. :) What happens when you let your foot off the gas after accelerating is that the ECM shuts off the injectors for a brief time. This is both for emissions and to prevent backfire among other things. The O2 readings will go to 0 has been my experience with a datalogger.
 

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Discussion Starter #6
throttle cable....

what is the best way to adjust this? i made sure the cable was tight when i screwed it back on to the intake. maybe too tight i guess. should there be a little slack then? how do i go about doing this the right way?

cheers,
 

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Discussion Starter #7
TTT
 

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you can adjust the tension by just loosening the 2 bolts on the bracket... it's right there on top and back of the plenum, right next to where the cable comes out of the black sleeve. You'll see that it can be moved back and forth. You want a LITTLE bit of play, but not a lot.

I still say (as I did in your previous post) you should do the NGKs. And I think the backfiring is more because of the gutted precats, IMO.

I'd also say to go to .032-.034 with gap BUT backfiring is usually un-burned gas and the smaller the gap, the smaller the spark and the more unburned gas....

It can't hurt to do the fuel filter anyway... plus that will mean you have to remove your battery, and when you re-hook it up your computer will reset. That can't hurt either.
 

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Discussion Starter #9
throttle body adjusted, now more problems...

ok, so i redid my throttle body cable last night. everything looked fine and everything ran fine.
i get up this morning to go to work, and my car starts, but the idle is all over the place. then it finally settles down to the bottom line on the tach(400 rpm i believe) and it just sticks there.
i drive off, couple of backfires, but everytime i stop the tach drops back down to about 400. so i turn around and limp it back to the house. as soon as i pull into the driveway, the check engine light comes on when it was down to 400rpm. when i depress the gas and bring the rpms up, the check engine light goes away.
these car problems are really starting to bug me and i am really missing the way my car is supposed to drive. does anyone have any ideas?
im gonna go ahead and change the fuel filter today, and see if that helps. even though it will probably wind up being something else.

frustrated,
 

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Wild guess here but sounds logical...

if your throttle cable was too tight (tight enough to actually RAISE the idle speed, which is entirely possible), the engine's computer may have gotten used to it idling at a high RPM. And may have adjusted itself to that setting.

If you let pressure off, now the cable isn't holding a higher RPM and the computer isn't used to "holding" the RPMs up... so it idles much slower.

Yes, change the fuel filter, again that will also by default mean you are unhooking the battery and resetting the computer. If it IS a computer setting problem then it will be fixed. Plus you'll have a new fuel filter which can't hurt.

When you start the car for the first time, let it idle for 10 minutes.
 

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Discussion Starter #11
thx JeremyG...

i gotta thank you a lot for all the insight and help you have given me so far. looks like i will pull the car into the garage this morning and start removing parts so as to get to my fuel filter. after i do that, ill leave it running for 10 mins or so like you said(will this hurt the engine if the check engine light comes back on??)
ill post my ongoing saga whenever i get more info.

thx again.
 

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Discussion Starter #12
forgot to add....

after i changed the plugs, there is a light hissing sound coming from the inlet area of the intake manifold. not from the throttle body to the intake manifold. this hiss goes away when the rpms are brought up.

not sure if this would have any bearing, but thought i would mention it anyway
 

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you most likely have a boost/vaccuum leak. This would explain your loss of power, backfiring, poor idle, etc. Check to make sure you didn't leave anything loose or not seat everything properly when you removed the manifold to do the plugs - check all vacuum lines, the clutch and brake booster lines, the rear turbo outlet pipe, ic hoses, EVERYTHING. If you have a leak, the MAS is measuring the air coming in but the air then goes somewhere else other than into the engine. This causes the engine to run rich and foul the plugs, misfire, send unburned gas out to the exhaust where it then burns.

If you have to, make a setup to pressureize the system and find your leak.
 

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Yep, ditto.

First place to look is your intake plenum and/or the throttle body gaskets. You are "supposed to" replace them EVERY TIME you take the plenum or TB off... many people don't and don't have a problem. I've seen some guys saying they've done it 20+ times with no problem.
 

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Discussion Starter #15
well, fuel pump is removed...

i had forgotten how much of a PITA that is, and it seemed pretty clogged. took me a lot of effort to blow air through it. the new bosch one i picked up will definitely improve that a bunch. i have taken off the throttle body as well.
the gaskets that are on the car are pretty new. 8k miles or so. i am pretty sure i can reuse them for now until i get a new set.
 

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Discussion Starter #16
ok, finally getting somewhere...

well, the fuel filter wasnt it. so i started to look for a boost leak. lo and behold, the 3 silicon hoses coming from the P,E,A on the throttle body had small holes in the bottom of them. more than likely i probably did this while i was tryin to seat the throttle body gasket when i replaced the plugs. looks like right now all i am going to need is some silicon hose.
this would cause all the problems i have been having so far right???
just wondering...and working to get this fixed,

cheers,
 

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93 octane, NGK BCPR6ES-11 or Champion #71, currently gapped at .035 with the MSD and Accel coils.
 
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