Engine Surge at Low RPM

[Eneme]

Hey guys, just recently got my 02 GT back after t56 swapping when 2nd gear shift fork bent in the tr3650. Car was running good I thought except for I quickly started noticing a little hesitation at cruising speeds and low rpm. However no codes at time.

It's been a few days and a tank of gas (to make sure wasn't bad gas). And now it's pretty consistently breaking up/surging at low rpm and load as well as throwing P0154(no signal bank 2) and P0173 (Bank 2 lean). Mainly noticeable in 5th/6th but sometimes noticeable in lower gears as well.

Going mid-high rpms it does just fine however. I'm hesistant to just think the breaking up is because of the dead 02 sensor however as breaking up would be caused of a misfire no?
Probably going to tear into it Sunday and check plugs and the like but wanted to see what anyone else might think. Btw car was brought to mechanic who put the t56 swap in for me to check if maybe one of the 02 sensors was just loose or unconnected and said everything looked fine.

Mods are:
Kooks LT headers/ Kooks Catted X-Pipe / Spintech mufflers
Accufab 70mm TB
SR performance CoP
Roush CAI (roush stage 2)
Bama tune

Everything but the alternator (SVE black alternator from LMR to replace whining old alt if it matters) was on and ran fine before broke 2nd gear shift fork and sat for 2 months.

 

[97gtconv.]

I'd check the wiring for the driver side o2 sensors to see if one is damaged/not plugged in from the transmission swap myself. check the o2 sensors with a obd2 reader that shows voltages for all of the o2's. See if any of them are lazy or dead. Is the car in closed loop? check engine light on?

 

[Mojo88]

Step one - thoroughly clean the MAF with the correct spray. I had similar rough running and surging issues and cleaning the MAF fixed me right up. Of course, this may not fix your particular problem, but it's always best to start with the basic stuff IMHO.

Good luck

 

[Revvv]

Like others have said, clean the MAY sensor. The CAI could have allowed a bit of oil to attack to the wires.

Do have the screen installed in front of the MAF?

Is the computer tuned for the intake?


Sent from my [device_name] using the svtperformance.com mobile app

 

[Eneme]

Will do with the MAF and i'l give the 02 sensors a check myself although i did have my mechanic take a 2nd look and he didn't notice anything out of the ordinary. And yes the car has been SCT tuned for all mods up to this point and didn't have any surging or problems up until it sat waiting for the t56 swap

I'll also check with the SCT in a couple days to check how the 02 voltages are running through the app on my phone, didn't even think of that! But yes the check engine light is on for the aforementioned P0154 and P0173

 

[97gtconv.]

maf cleaning wouldn't hurt it but a dead non reading o2 is a giveaway to a problem. check with your app to see the voltages and there movements. i use a blue tooth blue driver by Lemur.

 

[Mojo88]

If CEL on, then that becomes the priority. I made earlier post on assumption that no CEL. My bad. I'd still clean the MAF at some point though.

 

[Eneme]

So update, havn't gotten into tearing into it yet or cleaning MAF but went to start it to move it from street to driveway and at first it only started for like a second before dying. Then after priming the pump a couple times it started up but was visibly pissed off and running rough with a definite misfire. However running code reader again didn't give me any misfire on start up or specific cylinder misfire.

Leading me to believe it's either fuel pump, clogged/failing injector, or maybe just very dirty MAF lol. But i'll be getting into it tomorrow with at least cleaning MAF to see if it'll clean up and then if not checking plugs. Ordered new pump and injectors since I would need them anyways for when i finish getting the rest of my procharger setup all together

 

[zinda]

I had this same thing happen to me right after i bought my 2002 GT used with 70k miles, i had misleading codes for my o2 sensors, bought 2 new one and the codes increased to even more thsn there was originslly. Figured it has to be a vacuum leak, from my 40 years of dickin around with cars, (20 years were with carboraters and plenty of vacuum lines) i knew it had to be a leak. Since newer cars have so few vacuum lines now, it really makes finding the leak very simple. Theres a pvc valve on the passenger side valve cover. Positive crankcase ventelation valve, lets air travel in one direction through your motor.

Thrres a rubber hose that comes offvof your intake that creates the vacuum, check the underside of those hoses, it might be a 2 piece, mine was cracked nearly the entire length of the hose but was hidden on the bottom. I rrplaced that hose and put a new PCV valve in right away and my car ni longer ran like it had the workds biggest cam at idle. Anytime you have idle problems 90% will be vacuum leaks, 10% will be sticky throttle body valve butterfly.

So if you cant find a vacuum leak tgen remove your CAI and shoot some carb cleaner in the throtyle body and check with your finger to make sure itscopening and closing all the way. I wouldnt even start screwing around with your MAP or MAF sensors, you would have to run your car without an air filter to get it clogged up enough to alter your idle. Idle is when the least amount of air passes through it and has little affect on anything. Its job is to detect air as it passes quickly and sends a signsl to the computer which makes adjustments for optimal output in conjunction with your O2 sensors and adjusts timing with proper fuel injector flow to give max WOT (wide open throttle) output. The computer also uses cam timing sensors to make these adjustments along with a few other sensors like temp and prerecorded info from past driving habits stored in memory. If its not vacuum or sticky butterfly i will be amazed and will have to hear exactly what it is so i can be ready for the unusual and unlikely repairs i may face someday.

If it was your fuel pump or filter it would be noticable more when you give it gas not at idle since your fuel pump always has a constant pressure no matter what RPM the motor is at, thats what the return line back to your tank is for. I hope this makes sense, your fuel pump will shut off when it gets too hot and it will usually do it after its been running for a while, eventually the fuel pump motor will sieze from the heat and not be able to spin (they spin at around 10k RPM)! Keeping over a 1/4 tank of gas will help prolong the life of in tank fuel pumps, the gas cools the pumps.

 

[97gtconv.]

look into the o2's and than check for vac leaks like mentioned above. you might have to get a smoke machine on it.

 

[zinda]

look into the o2's and than check for vac leaks like mentioned above. you might have to get a smoke machine on it.

Are you talking about a gas analyser when you say smoke machine?
When i was going to school at a auto repsir school (IIwont say which one since i found it to be a complete waste of time and money, everything thet taught can be learned by reading any chilton repair manuals introduction area (the part most people skip and never read unless they are forced to!)) I decided to quit the school once i used the 5 gas analyser.

I found them to be contradictory and absolutely useless, at leadt the one that i usef was. I had an '89 GT 5.0 HO and had the leaking fuel injectors due to the cracked plastic top pieces, they were tan colred, 6 of 8 were cracked. The analyser showed no such issue, turned out a perfect report. Pulled 2 plug wires and still fidnt show the correct read out which shoukd have shown high amounts if unburnt gas. The fuel injectirs were replaced and tested it again, (it then would hold fuel pressure so i know there were no problems with fuel input) got the same exact results.

I knew what was supposed to be shown with each problem but never could get the results to show anything close to correct when i putposrky altered settings, paritally blocked the air filer, pulled a vacuum line, started cold then hot, pulled sensor wires, it eouls change but never reflected what i was taught it should read.

So my experience was so flawed i saw no real life application even though in theory it shoukd be your main go to device to shiw where you are at. I found a simple handheld OBD tester will provide the info needed as long as you understand how they workvand why they will sometimes be so far off from reality, misleading most novice users intobtearing their cars apart to fix super simple problrms such as this one has done for the OP.

All testers have a flow chart whichbshows the order that tests are done, if it csnnot finish 1 test it might skip to the next or show an error or give a fslse report based on how far it was able to get. When anything is skipped or readings are compromised by unable to read or false readings due to improperly functioning sensors that are not being seen as bad but rather just inaccurately reporting readings, will make troubleshooting impossible with OBD testing.

These tools are useful only when you have the knowledge of what they do, and how they do it, simpky knowing how to get readings reported on the screen will not be able to get any answers that are pointing you to what the actual problem is, as most everyone who has used those tools already knows all too well.

My OBD tester hadnt been used since i i tri to dolve this same issue, i found that they are more of a misdirection and seem to never provide any clear answrs as they claim to be able to do. This is why you dont see the things flying off the shevles or even have sny resale value. Most mechanics know their limtations and only use it to find infonthey know they csn rely on to be accurate.

The only useful function they have is the recording feature that shows resl time readings, no tests are being done unless you place it in test mode, you find the test it cannot complete and see where it is on the flowchart to see where it stopped or what could be the readon it cannot complete the tests. They never simply trll you whats wrong, thats how they shoukd work but none have ever been able to do that correctly and they error codes are ususlly thriwn becayse it cannot complete a test, whete it stops is not always the issue, if you have 2 issues youll never get the tools to ever come close to whats really wrong.

Dont base your repairs solely on error codes alone, its more important to understand how the tests are done and once you undrrstand that you dont need the tools in the first place, since they never tell you exactly what you need to do snyway.
Im sure this is nothing new to expetienced mechs, but when i see repaiirs based solely on OBD readers i have to assume the owners are not familiar with doing much troubleshooting work or using those tools. They can be helpfull in the right hands but should not be considered to point you accurately to every issue, maybe 1 in 10 codes will be pointing to the real problems, i myself have no use for them and sold my 4 high priced tools and kits, ive saved money by not being mislead by them.

 

[97gtconv.]

smoke machine that gets hooked up to vacuum hose on the intake. smoke is used to expose vacuum leaks. i had one i bought from harbor freight. worked pretty good. so if you clear all the codes and fire the car up and the check engine light comes on what's the first one?

 

[zinda]

Ok, i used smoke bulbs before while testing airflow at motorola, they had a trailer that was used for various plating plating types. They had acvat of chemicals all lined up in a row back to back down the middle of the trailer and they had an exhaust hood that sucjed the fumes out. We adjusted the airflow to be sure all funes were venting properly and none were floating past the hood.

It was like a small turkey baster that pudhed out a very large thick puff of smoke, when you squeezed the bulb. Im not sure what good theyll do detdetecting vacuum leaks, usually the trick is to spary dome starting fluid around the hoses snd see if the idle goes up. With only 1 line to check i think a visual inspection will do just fine.

 

[zinda]

smoke machine that gets hooked up to vacuum hose on the intake. smoke is used to expose vacuum leaks. i had one i bought from harbor freight. worked pretty good. so if you clear all the codes and fire the car up and the check engine light comes on what's the first one?

Im not sure what you are asking here, when you clear the codes and the check engine light comes on right away, its telling you that theres a problem that has not been fuxed since the code was posted originally. If its a vacuum leak it could interfere with almost every test that the car tries to do. Once the O2 sensors try to adjust the output unsucessfully, it throws a cide. The sensors see too much gas and the comp trues tr lean it and it still senses too much gas, the computer thinks the O2 sensirs are bad. It diesnt jniw that theres a vscuum leak thats thriwing off the air idle mixture. It just knows that it cannit compensate for the high or low readings and quits testing at that point. The O2 sensors are constantly beingbmonitoredvat all times, they are the 5 gas analysers that are built into the car. They test the output for unburnt gas or too much carbon or any other residual left over gases as tgry leave the cumbustion chamber. Theres some cokd starting modes tgat are in place to act as a "Choke" thus tupplies extra gas to the cylinders while the car warms up. Gas will become more volitle when its hot, too hot and it burns up before its detonated. This uscwhere higher octsne gas plays its role in higher prrformsnce cars especually high compression engines.

The gas will compress and just that comoression alone will cause "predetonation* thats the pinging noise. Thats the cylinders firing off the top dead center mark, this can be just a split second befire the computer wsnts the plug to fire the gas and it msy be abke to comoensate by adjusting timing and opening injectors more to kerp gas from evaporating since the gas will cool the cykinders chamber, more gas will cool it more.

Thus is how deisel engines work and thats why the term deiseling is given to cars that keep running after the key is turned off. The heat and compression are enough to fire it untill the cylinders run out of available gas in the lines. Without your electronic fuel pump running it only has pressure thats in line to do this, carborated engines with mechanical pumps can deisle for a long time, ive seen them go for a few minutes. If the key us turned back on the car will resume running or sometimes blow the exhaust apart from all the accumulated unburnt gas that is produced from the deiiseling, it no longer has the spark to burn off the residue and its pumoed out into the exhaust, builds up, then the spark fures a flame ingo the exhaust pipes and the mufflers explode, mostly on single exhaust cars.

 

[Eneme]

New update! So replaced injectors(needed new ones anyways as after all this gets perfectly sorted im getting a procharger setup installed), spark plugs, and coils. After getting a new tune from BAMA and uploading it, the car seemed to drive fine for awhile (like before) but has slowly been getting back to the problem it had before of running rough at cruising on freeway.

However, NO CELs atm.

When I noticed the car started getting its weird sporadic surging again, I started looking at the short/long term fuel trim on both banks and am noticing that when cruising, both banks are never near each other (both are off anywhere from .2-.4, ex: bank 1 reads like .85, bank 2 reads 1.2 for long and short reads .95 bank 1 and .75 bank 2). But when i decide to give it a little more throttle then cruising or even get on it a bit, everything clears up to damn near perfect with both banks reading similar readings.

Suspecting maybe one of the bank 2 sensors is on the fritz even though i replaced them less than 2 years ago when i did long tubes.

 

[97gtconv.]

Could swap the front O2 sensors and see if it changes or stays the same. I'd check for soot marks on your long tube to mid pipe connections and for leaks and around the exhaust manifold flange for a leak. check for vac leaks, might have to get your hands on a smoke machine..

 

[Eneme]

Yea that's a possibility, but probably won't get around to it till this weekend. Will try to keep the thread updated