help with 3.2MTX running rough

[redshoman]

Background: '93 ATX to MTX, 3.2L bolck and heads, XJ2 computer, 3.0 intake cames, 3.2 injectors and rails, underdrives, cold air, catless SHO source y-pipe, single exhause out to cherry bomb muffler.

Swapped the MTX in and the 3.0 cams in the engine. 60k done. 3.0 timing componets and serp system. Car ran ok, but a little rough, I just figured it was because of the incrased desplacement and cam change. continued to get 3 codes, IAC circuit voltage high, and both banks lean. (contrary to IAC issue, car idles great 800-850). Connected car to SBDS and found compression (running and static) were all good 175psi, spark duration ware all great, injector pulses were all even and great, fuel pressure was at 32psi idle and up to 45 at WOT.

Got SCT chip from Doug at FPS (who is awsome and has helped me tons), and missfires at idle much more noticable and falls on its face under load. on power balance it's a completly random missfire. Take chip out and still missfires just a little less. I know its not the chip causing the issue, its only making it more noticable. When it missfires badly its puffing almost raw fuel out the tailpipe (the extent of the missfire), and get the exact same codes with or without the chip

I started testing and trying other parts. I replace the MAF, IAC, TP, DIS, intake, vacume tested the intake system and replaced a few vacume lines that were questionable, coil pack... plugs, wires, cam and crank sensors from 60k...I pressurized the coolant system and had no drop hot or cold and did not find any leakage with an elctronc borascope in any cylinder. I could not nail anything down, so i started elimnating the possabliltys the best i could.

I have been fighting with the issue for 3 weeks now and gotten help from a few great people, but I am running short on ideas and was wondering if there were any other SHO guru's out there that could throw me any other bones, have a whole weekend off and would hate to not spend it diaging..

 

[shospeed143]

well it looks like you have checked or replaced every thing but the O2 sensors. So if I were you I would start by checking them, lean volts is .01, rich volts .09 if it says that it is running lean then the O2s might be bad and that would cause your problems.

 

[redshoman]

miss fire or running lean.. its still going to show .01v... if its lean than, self expalintory, if its missing than the unburned fuel and air pass the 02 and still show .01v.. its a chicken or egg thing. I another good idea to try. I guess I'll hook up the ole Break Out Box and see what they are reading... just hate to throw 2 02 sensors at it.. very rare that both would fail.. I would lean more to the miss fire causing the lean codes, that leads me to my real question: why a random missfire on any cylinder??? God my brain is fried trying to figure this out.. thanks for the idea

 

[lowc]

sounds like you might be off on the timming. did you use the 3.2 or 3.0 gears if so

NovaSS
Project MINIGUN
Join Date: Aug 2005
Location: Maryland
Posts: 452




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The only thing goffy about the swap is the marking on the cams to align them with the chain drive sprockets between the intake and exhaust cam, the 3.0 cams have dots that line up but the 3.2 cams are marked "funny" and dont line up with the dots on the sprockets.

thanks nova
this may help

 

[redshoman]

I used the 3.0 intake and gear and sproket that originaly that came on it, and I used the 3.2 Exhaust cam and sproket. I did use the all the correct timing tools. I lined everthing up with in the 3.0 order because of the 3.0 serp system and timing system that I used. I was really leaning toward the timing.. but wouldn't the relitive compresion be off? all cylinders are about 175psi. Im wondering if what you say about the 3.2 is where my issue is? I can quite remember weather I lined up the cam dots with the sproket dots or not, I remember them and know I alighned them on the exhaust but intake???? I know I lined the cam spoket dots with the dots on the timing cover, but the 3.2 exhaust cames to the cam pullies i dont know... hmmm. Defitnly worth looking into,

Thank you

 

[lowc]

compresion will not be affected everything is still opening and closeing its the timming of fuel induction and exhast extraction that is effected. i belive that if you contact nova ss he has pics of where the cams should be lined up with the different cam gears

 

[redshoman]

So I re-recorded the codes that continue to come up:

551-Idle Air Control (IAC) circuit failure KOEO,
172-Lack of heated Oxygen sensor (HO2S-1) switches, indicates lean (Bank #1),
176-Lack of heated Oxygen sensor (HO2S-2) switches, indicates lean (Bank #2)

I replaced the IAC and code still continues to come up. While running, If I unplug the IAC it does die, so I know its doing something, just unclear why it contiues to fail KOEO, I tested the resitance and it's within speck...

 

[rick-ng]

o2s!....

 

[redshoman]

Installed 2 brand new 02 sensors... nothing changed.....

 

[SHOtime2511]

clean your IAC valve.

 

[redshoman]

I replaced it with a known good one, still cleaned what was in there.. same result

 

[redshoman]

after driving for a bit, the Check engine light now does not come on, but the idle does, drop down when in closed loop, and is gutless at 2-4k without chip. I havent re pulled codes... but im guessing that the lean codes are gone.. but still runs like pooh... on to the next issue

 

[lowc]

i know you said you did a vacume test but try this run the veh and take some brake clean and spray it around the intake and vac lines and listen to the motor and pay attention to where you spray if idle rises you have a vac leak some where in the area you are sprayin. do you have a egr system?

 

[SHOtime2511]

both banks are reading lean?
its got to be a mass air meter issue or a vac leak.

 

[redshoman]

I can watch the o2 sensors and I have done that, I watched and listened. I put propane everywhere. The O2's are reading and switching correctly now. It is a compound issue I am having, thats how i know I do not have a vacume leak, I can watc live straming data and see if theres a vacume leak. I also smoke-pressurized the system and saw no leaks, it does hold vacume when the y-pipe and throttle body are sealed. Tried 2 MAF's and both read the same cannot see any dead spots on the screan ( live data graph).

Now that the o2s are reading correctly, I am still having a problem where it falls on its face and miss a bit, than comes back to life. I have thrown every part I can think of at it, and all streaming data looks normal. Maybe the "new" crank sensor is unhappy. I guess I will try to connect it to a sillascope
Thanks for the idea's guys, keep'em comming I appreciate all the help!

 

[zak]

Are you using the ATX wiring harness? A number of problems could ensue:

1.) The ATX uses indvidual 4 wire sensors with indvidual grounds running back to the EEC. The X2J uses only a single block ground for O2 IIRC. Check to make sure your harness and X2J are compatible enough in pinout to get a good ground signal back to the comp.

2.) Focus also on the hard fault you are getting on the IAC - see what voltages you get at the connector. This could be do to (again) a mis-pinning issue between the X2J and the ATX engine harness. SHOaz might know more about this, he is purported to be smart ;-)

If it helps any I am looking to buy a decent condition ATX engine harness . . .

 

[redshoman]

I used the entire MTX engine harness and computer, the 3 pin 02 sensors and only had to swap a few pins in C122 and C116 to make it work, but that was all with starter and a/c.

I still have my ATX harness.. PM me if you want

Thank you

 

[redshoman]

Update: well vacume leak was correct!!!.. KINDA... The IMRC solinoid had an internal leak. I replaced that and the car woke right up!!! Drove all around no more codes dead spots, dosent smell fuely or smoke seems happy as a clam. I put the chip back in, and it cannot get out of its own way again, falls flat any time I give it gas, even misses and farts at idle. super bummed, but without the SCT chip it is way fun and has gobbs of torque. Now I have to find out what the chip wants too see that its not getting... guess I'll leave that for the weekend.

Thank you all for your help! Pumped about all the support!

 

[lowc]

glad to see you got it.

 

[SHOtime2511]

Amazing what a tiny vac leak will do isn't it?