mis-firing and bucking

[Blackened302]

so i'm having a bit of trouble w/ the new set-up (see sig)... mis-firing and bucking. it happens at cruise-speed, wot, and at idle. strangely, though, sometimes it's like a switch is flipped and it'll run smooth for a while, but that's always ephemeral.

a few details:
-i'm on the stock t4m0 w/ the tweecer, but all my tunes are based very closely on the stock tune
-still on 19#ers and stock maf
-explorer throttle body
-no fuel pressure regulator
-timing at the dizz is set to 10*

i've checked that all the spark plug wires are well-connected, and i'm running all my stock sensors (tps, iac, etc..).

hoping to get this cleared up by monday so i can get myself to school/work monday morning. any help is appreciated, gents.

 

[HISSIN50]

Paul, I have to ask the stupid question first.......... (anyone who uses the term ephemeral can handle it. ).

What's with your FPR comment? You don't have an adjustable FPR or you blew our socks off with a returnless system?

If it will happen while idling, can you start goosing all the harnesses to see if something changes? Are any codes stored away?

What's the EGR situation for you? If there is still an EGR valve, it might get stuck open a little bit (carbon in the seat or a leaking EVR).......

I really don't have any great ideas for ya mang, but I figured I'd give moral support.

Good luck Paul.

 

[OrangeMustangGt]

verify you have good plugs and gap....also wires/cap,rotor.

that is a common symptom of that problem


btw, have you dynoed that combo? what cam did you use? the explorer intake sucks also......it held my car back alot when i dyno'd my similar combo

 

[BlownFiveLiter]

Sounds like the symptoms of a bad MAF. When it's happening and you put it to the floor, does it seem like the car can't get out of its own way? I'm also curious about the FPR thing, but I'm thinking inside the box for the moment (we all know JT doesn't do that! ) and just believing that you mean you're still running the stocker, but not an adjustable one.

 

[Blackened302]

hehe, yeah, i meant to say i still have the stock fuel pressure reg. i guess it doesn't matter as much as i thought, though.

egr is gone--turned it off w/ the tweecer, too. smog's also out the door.

the plugs were gapped (though i am going to get new ones asap), i've checked the wires numerous times. the check engine light just came on last night, so i'm gonna pull the codes asap.

the few tunes i've managed to try out are simply variations of the stock tune--all i've changed are fan speeds and idles.

haven't dynoed the new combo--haven't even raced any of my buddies. don't know the specs on the cam, but i know it's a nitrous cam from comp cams--has a nice lope to it. the intake i have no complaints about so far, but what do i know, hehe. the runners were gasket-matched, if that helps.

about the maf: no, if i step on it, it'll move, but sometimes it'll buck pretty badly.

i'll take care of the new plugs, wires, and pulling the codes as soon as i can (hopefully today) and i'll get back to you guys. i sincerely appreciate the help/moral support--thanks!

 

[final5-0]

IMHO ... the prob is NOT in the Tune

You got something mechanical goin on

Get all those loose ends tied up
and then
Commence on the tune thing

Grady

 

[Blackened302]

yeah, i have to agree. i admit that i initially thought it may have been the tune, but when i realized that i'm running a slightly modified stock tune (idle speed raised, fans come on sooner) i come to the see how you, grady, and the other guy suggested it was a mechanical problem.

now that i think about it, the plugs we used were originally on the explorer engine and were black a little, so i'm gonna change them out tomorrow, if not today.

once again, great to know i can look to you gentlemen for help/guidance. hopefully next time i reply will be to tell you the problem's fixed!

 

[final5-0]

Just ensure everything like v leaks, bad electrical connections,
faulty sensors, plug wires, etc are in good working order

B E C A U S E

If any of the above stuff is in place
It could hose up your tuning efforts

and

Make you all like

and then

You'll be all like

and finally

You'll come on here cryin and all ... Sayin ...
Nothin is workin with my tunin

Don't EVEN ask me how I know all that stuff

It'll be Fine ... You can Do It
and
Like Larry the Cable Guy says

Gitter Done

Grady

 

[Blackened302]

just finished putting in new plugs--made sure the wires were connected well.

scanned the codes--all i got was #51: ect sensor voltage too high. i'm guessing that's the sensor that is in the overflow tank? no wait, that's the low coolant sensor, no? either way, i don't see how that would affect mis-firing/bucking.

the car bucked a little less, but i can still hear a mis-firing.

the cap and rotor are about 8 months old, the wires are about 4 months old.

any other suggestions? thanks.

 

[HISSIN50]

Paul, how'd you get a two digit code (I don't ask to be a smarty but I didn't think you had done an A9* swap)?

The ECT circuit is the sensor on the passenger heater rail for the computer. It relates coolant temps for A/F trim as well as fan control. It's a biggie. If the reading is always high, there could be a wiring issue. I'd check the voltage with the car cold vs hot, as well as disconnecting the E-connector and testing resistance hot vs cold (remember, it's a thermistor, so resistance and voltage both go up or both go down).

I'd add that if you started the car without the sensor hooked up, this could toss a code.
Good luck bud.

 

[Blackened302]

hmm, weird? that's what the little print-out said--51. i'm on the stock 'puter.

got any more details on the ect sensor, JT? are there any vaccum lines going to it or is it purely electrical? what's it look like? thanks, man.

 

[Kr33p]

Do you at least have some sort of MSD box mine bucked and stuttered from a lack of spark. If you need a MAF I'll be willing to lend you my stock one.

 

[Blackened302]

i have a pro-m maf calibrated for 24#rs, but don't have the injectors yet so i'm still running my stock maf + injectors.

no msd ignition, either.

 

[HISSIN50]

hmm, weird? that's what the little print-out said--51. i'm on the stock 'puter.

got any more details on the ect sensor, JT? are there any vaccum lines going to it or is it purely electrical? what's it look like? thanks, man.

For quick testing of the ECT:
Look for about 3.0 volts at 70*F.
Or .80V at 180*F

Then if you disconnect the sensor's E-connector and check resistance across the ECT's terminals:
Look for ~37000 Ohms at 70*F
Or 3800 Ohms at 180*F.

Those are both important points (cold start and operating temps) and let you know how calibrated the ECT is.

Check out this cool diagram (courtesy of my bud Tim [Stang22], who said he got it from Almost Stock):

View attachment 401399

Look in the area of #7 (note this is fox based, but so many things are so close).

 

[Blackened302]

thanks, buddy--a pic is worth a thousand words! i was thinking you meant looking around in the area of 57 in that pic, hehe.

gonna check that out tomorrow, then (along w/ cleaning the iac, tps, and maf). thanks again, mang!

 

[final5-0]

I just quickly passed over this whole thread as I gotta go

BUT

If you got 24's and are runnin an unmodified t4m0 with
the OEM maf

You are too fat!

Grady

 

[tjh566]

In one of his posts he says he is using stock maf and injectors, until he gets his new injectors in.

And while i was out tuning yesterday, I burnt a new tune onto the tweecer and the car started to run horribly, re-burnt the same tune and it was fine agian, i guess it go corrupted on the transfer to the tweecer or something. Just a thought to consider.

 

[Bosko5.0]

could it be a crossfire?????

 

[Blackened302]

i'm in the process of cleaning my maf, tps, and iac. that should help, plus the new plugs i put in last night.

i'll recheck the firing order, though we did it using a chilton's so i'm sure it's correct.

grady--i'm still on the stock maf and stock 19#ers. i have a maf for 24's but haven't put it in yet as i don't have the 24#ers.

 

[HISSIN50]

i'll recheck the firing order, though we did it using a chilton's so i'm sure it's correct.

Mr Paul, I dont have a Chiltons for the stangs. However, I have the other manual (not a Clymer) for a GM we have. And wouldn't ya know the firing order is listed incorrectly in that book.
Not to say it is listed incorrect in your book for stangs, but I now always double check the listed FO's with another source to make sure I'm gonna be good.

If no one covered it, try running a cylinder balance test - it really saves time trying to diagnose which cylinders are not contributing.

Good luck.