Ok guys ive been experiencing this problem for a while. i have a 91 camaro lo3 5 speed. kinda modded. with 3 inch exaust and headers. bored 30 over. open element. but the problem is at light throttle going about 1500-2500 rpms in first, it chuggs and surges for like a second like there is no fuel going to the tbi and it makes this popping sound and raise rpm back again and sometime does it again. and it will happent at any gear. even if im cruising at 70 mph and speed up to 80 mph in 5th, it will do this surge chugging popping syndrome. its bugging.. people on the road think i dont know how to drive because it feels like the first day i drove a stick, that back and forth jerk when shifting gears. and it feels like theres no horsepower on the engine.. ive done some datalogging but everytime i do datalogg i dont experience the problem. it doesnt happen all the times.. theres days it runs like a champ. it can be hot or cold when i experience this problem.. i can attach a recent data log. yea i notice i run rich and lean.. and the last time i data logged today it had lots of spark counts. and i know for a fact that i have a exhaust leak on the driver side header. i would like to solve this and ive read alot of people are have the same problem with no luck. i know there are lots of smart guys on this board.. let cure this syndrome fast.
Joseph

 

so it's like pinging? maybe your timing is off? defective knkock sensor or something? overdrive isnt really a gear you wanna be doing acceleration in,its a crusing gear

 

its kinda hard to tell if it pings because of the exhaust leak. when im in 5th gear going 70 to 80 its not like im punching it to WOT. i just want to make a pass and it will act up.. im going to go for like a 30 min drive and im going to datalogg it.. timing doesnt seem like a problem but i check into that.

 

ok guys i datalogged the car for about 30 mins.. ill attach the log. but i saw lots of bad things.. i was running rich and lean real bad. also i had real bad spark counts. and i got a asynchronous fuel flag one time during the drive.. not sure what that meant.. but i was experiencing the syndrome i explain in the first post.. i also replace the driver side header gasket and found a new leak. on the passanger side header flange where it meets the y pipe.. i didnt replace this due to access of a jack i will this weekend... but i was wondering.. this is my theory.. can that leak at the y pipe flange cause real bad knock to the knock sensor. which the computer then retards the timing and make my car run like crap. and surge during light acceleration. will that also make the car run real rich and lean? or is it a bad O2 sensor? take a look at the log.. BMonteSS i need you on this one.. your smart at reading logs.

 

i also notice my tps voltage is all over the place. Can that be bad?

 

Damn....I'm having the same exact problem. Except my car is stock with exception of the open element air cleaner, but the car was doing the same thing before I installed the air cleaner. Completely stock it was doing it.

Light throttle to pass and it bogs down...drop a gear and WOT and it doesn't want to go.

 

OK...here's an update...

Since I don't have the luxery of a scantool I decided to try something.

It felt like timing was being pulled out of it so on the ESC box plug, I pulled the contact for the knock sensor (too hard to get to with all that AIR crap in the way.) Decided to tap on the block with a screwdriver and watch the output while I did it.
https://www.thirdgen.org/forums/tbi/...est-knock.html
voltsAC was all over the place, yet there was NO discernable ping or knock. So I left it disconnected and test drove it.
What a difference!!! Considering I'm used to listening for knocks on carbureted engines, I heard none. Light throttle, mid throttle, WOT...no pings, no knocks, and had tons of power. Hell...earlier today the roads were wet and I couldn't even break the tires loose, but now...hehe Much better.

My AC compressor makes a ton of noise (time to replace it) and the power loss was greatest with the AC on so I'm thinking that it was picking up that noise.

I know that the computer runs the spark as well as balancing the AF ratio. If I were to leave the ESC disconnected (like it is now), and put in a standard distributor and ignition box (6AL), do you think there would be a problem? Besides the PROM throwing a SES light, it would still be using the MAF IAT and O2 sensors for running the injectors, right? It doesn't use the ESC box for computing AF ratio does it?

Tom

 

I had the same exact problem on a stock lo3 with minor mods......It was the simplist thing....The EGR Valve...check that...simply unplug and plug the vacuum line and try driving it...let me know if it works....I block mine off(no emissions here).....simple yet effective...hope it helps...Dave

 

I was thinking about that one too, but I know my EGR was working. I may plug it off and try it that way tomorrow as well.

Worse case scenario, I pull the whole shebang off and drop a Holley on it! LOL I know carbs...this EFI is for the birds. LOL

 

gotta love this efi in the winter and first thing in the morning though...(easy starts)...yeah plug it off and see what happens

 

i have a question on the egr valve.. i had my car running and unpluged the vacuum line from the egr and to me there was no vacuum on the line.. i also put my finger over the egr valve and there was no difference on the engine.. is there suppose to be air going through the vacuum line? or some sort of flow?

 

there should be a small amount of vacuum I believe until you accelerate then the vacuum becomes stronger...I believe because when you accelerate the diaphram opens up.. but I could be wrong maby someone can chime in and correct me if I'm wrong....if there is no vacuum what so ever you need to chase the line and make sure its connected on the other end....
just plug the line and drive it...try that first and you may get your answer....

 

ill have to look at that again.. and about grounding the knock sensor. where exactly is that located? and how do i ground the knock sensor? i think my exhaust may be interfering with my knock sensor and it may be causing my ECM to retard the timing. I've come to three different conclusions...1) my EGR 2) my knock sensor 3) my timing or distributor cap....i am going to take a look at these potential problems and see if i can track the main reason...i pm'd BMmonteSS since he's very intelligent in reading datalogs. my TPS voltage is all over the place and from what ive read it is supposed to be a steady voltage so that may be a problem as well. so we will have to wait and see until he stops by the thread and leaves a comment with what he thinks might be wrong.

 

I did not ground my knock sensor, I just disconnected it. On the drivers side of the engine bay firewall...there is a small black box with a flat 5 post connectro with 4 wires in it. when you take it off, remove the wire-holder-plasitc off the back and put a paperclip in the release spot (the plug from box goes into the main spot, and a small space for both ends of a peperclip fit into the smaller space of the same receptacle) then pull on the wire. The whole wire and connector should come out easily...DO NOT FORCE IT OUT!!

That basically removes the knock sensor without cutting anything. (The only reason I do it this way is because I can't reach the sensor, otherwise just unplug it there.)


The EGR should not have any vacuum at idle or WOT, but good vacuum when you press the gas partway, and at cruise. If you have vacuum at idle, the solenoid may be bad or leaking.

 

thats what I thought but couldn't remember exectly thanks for clearing that up..I hate to give wrong advice....

 

if u need a solenoid id gladly save you the money i have a good 1

 

Sorry I didn't get to this sooner, but I finally took a look at your log.

First of all, you have to keep in mind that the TBI ECM only sends a snap shot of all the readings about once every second. You can get the throttle to the floor and let back off in this time period and you can completely miss it in the log. This is why your TPS appears to be reading all over the place, it looks fine to me. Also your O2 voltage is the same way, it actually crosses over .45 volts somewhere between 20 and 60 times a second. As you can imagine the O2 voltage in your log is about useless.

With that said your fueling looks to be pretty decent (within 5%). You did seem to be getting an unusuall amount of knock counts. I couln't trace down any causes that were related to the tune of the motor, so that pretty much leaves that up to some kind of false knock.

Knock in the quantities you see probably wouldn't cause constant drivability problems. I did see 2 codes set for a high TPS and a Low CTS, have you had these sensors unplugged with the ignition turned on? If not they could be an indication that these sensors are getting flaky. In this log they appeared to be working just fine.

Kind of a complex problem, and there really isn't an easy answer. I would start by unhooking the knock sensor when it starts to act up. If the problem is instantly solved then it is the false knock causing it. Keep in mind that you can NOT leave the knock sensor unhooked. The ECM does a self test to make sure it's working, if you fail this test then it will lock the timing at 20 deg and make the motor run like poo.

If the knock sensor isn't the problem you might try replacing the TPS and CTS just to see if it helps. I've seen sensors give a dirty signal before that shows up ok in a log but in reality are reading funky.

 

update
i installed a new knock sensor and new passenger flange gasket yesterday.. it ran alot better but i was getting the rattling sound like the timing chain. well this morning it did do it but when i was driving home from the gym it didnt made the rattling noise it ran like it used to.. is it still like a retard timing situation? does it take awhile for the ecm to adapt to the new sensor?
Joseph

 

well today i was driving back home from work. and its started doing the rattling noise.. it has to be the ecm retarding the timing.. my thing is what is causing it to retard the timing.. it was running fine yesterday and today it started acting up.. im going to datalog it and see what i see different.

 

EGR--------------my car has been doing the same thing to the tee thats what mine was!

 

is there any way i can troubleshoot the egr to verify if its not working properly? i just dont want to spend another $60 on a new egr and thats not the problem.. these cars can get pricy at times.. its part of owning a 16 year old car.

 

well unplug the vaccum off the egr while its running and if it runs crappy still its bad. if u unhook the vaccum and she runs worse its functioning. i got mine at advance or autozone for like 40 bucks