part throttle sputtering and backfiring *UPDATE* Code 42??
 

Sorry if this post runs long, I have searched here for hours and not found anything close to my current problem so I'm trying to be as descriptive as possible. So I developed a new problem driving my gf to work tonight. At highway speed it suddenly started to buck and backfire with a constant rhythm, almost like a heartbeat. This happens only at medium throttle, if I barely keep my toe on the accelerator or give it more than 60%or so it is fine, bit in between its barely driveable. This leads me to think tps? Or something along those lines? I've had a slight problem since I got the cartl that was very similar but not nearly as serious where right when I start her up ill get an ever so slight hesitation at slight throttle that goes away after about 5 minutes. I'm thinking this is related and is definitely a sensor on its way out. No codes, but I've only driven it about 10 miles since it started acting up.

Again sorry about the long post, but any help in the right direction would be great. This is my DD and my baby that I've brought back from the grave from a stupid teenager destroying it.

Re: part throttle sputtering and backfiring
 

You can check the TPS in action by backprobing the 5V reference INPUT, and 5V return TO ECM with a pin stuck in the backside each respective socket - one at a time.

https://lh4.googleusercontent.com/-f...0/IMG_5556.JPG

Full TPS workup here:

http://www.zr1.net/forum/showthread.php?t=20793

Re: part throttle sputtering and backfiring
 

Thanks much, I was actually under the hood as you posted this. Unless I'm doing something wrong, my tps is definitely shot. I tried every combination of the three prongs and never got so much as a blip of activity. I also checked the cts as I've seen that may cause driveability problems and I got a nice even 5v. So I'm guessing I was correct in assuming my previous might or missing was the tps on its way out and it finally kicked the bucket last night. I'm replacing it in a few hours and ill post the results.

Re: part throttle sputtering and backfiring
 

OK - wait a minute here...

If you had the ignition switched ON, you should have a 5V ref input - broken TPS or not...

Re: part throttle sputtering and backfiring
 

:idiot: yeah, I'm a dumbass. I did it the RIGHT way with two paper clip pieces in the sockets. Got almost dead even 5v, although still nothing when moving the throttle. I get about .33 there and it doesn't move at all. That doesn't sound right either but i can't imagine how I could have done it wrong again.

Re: part throttle sputtering and backfiring
 

Sounds like the TPS' potentiometer needs butter (might be toast).

Check impedance fluctuation in range of swing arm motion, as shown in the link on the other boards there...

Re: part throttle sputtering and backfiring
 

ahhh - why link to other boards - I don't mind looking at my own pics (even tho' they don't tell much)

I was trying to determine if it's linear or exponential potentiometer. Looks exponential too, but that's still an open book case...

baseline:

https://lh6.googleusercontent.com/-B...0/IMG_5541.JPG

ROM pegged:

https://lh6.googleusercontent.com/-E...0/IMG_5542.JPG

midway ROM:

https://lh3.googleusercontent.com/-c...0/IMG_5543.JPG

Re: part throttle sputtering and backfiring
 

ok so I should be looking for lower resistance as the throttle opens instead of a rise in voltage. What would this tell me if I get a linear reading? Something I can fix for free (always my favorite)?

Re: part throttle sputtering and backfiring
 

Yep - mine DOES work.

Baseline = highest resistance, pegged = lowest resistance. Work the arm slowly, look for skips in reading. Should be steady lower resistance as you sweep.

And you can check the Gray wire - the TPS signal FROM the ECM, should be 5V, grounded to frame or block, ignition ON, then check to see if it grounds properly TO the Dk Blue wire - the 5 volt reference TO the ECM.

Black wire should ground properly too - try 12v[?] to the Black...

(colors might be different - this for '90 LT5...)

Re: part throttle sputtering and backfiring
 

It definitely had adead spot so i replaced it. went about 20 miles no problems, then it started it's **** again. Even stalled out at a red light and refused to start until I reset the ECM and disconnected the TPS. Is it possible to twist it on wrong? I thought 91-92 weren't adjustable? Only code I got was of course 22 from me unplugging the sensor. IF it was twisted wrong, any chance I can pu it on the other way since I only drive a short distance or is it just shot?

Re: part throttle sputtering and backfiring
 

Twisted? Doesn't it push on, with a weatherproof connector?

Test it same way, for decreasing resistance. Then plug it in, and check resting voltage with a backprobe, to the block or frame. Should be about 1/2 V. Open the throttle linkage, and check for about 5V. Then check by putting the backprobe in the RETURN TO ECM socket, to see if it still shows same voltage at base and at WOT.

Sure is a pain - ain't it? But ya' have to do it.

Re: part throttle sputtering and backfiring
 

Haha yeah it's definitely a pain. It tested ok so i'm about to take it for a test drive. I definitely put it on wrong, it doesn't just go straight on, you have to put it on slightly crooked to line the two pieces up. When i put it on earlier I had to rotate it about an inch counter clockwise to line the holes up, i did it the other way just now and it only went about 1/4 inch clockwise... Hopefully I didn;t stretch the spring out inside it. Thanks for the fast replies, I'll post later if it works.

Edit: Damn that TPS must have been bad since I had the car. Throttle response is a bit better and i don't smell any unburnt fuel out of the exhaust. For anyone reading in the future with this problem, make sure you twist the sensor on clockwise with the front "block" part of the sensor pointing up and then down to make it sit flush. PRobably not a common problem people have but I can be a bit of a dumbass sometimes so if that helps one person I'lll be happy. You are the man, Schrade. Thanks for the help.

Re: part throttle sputtering and backfiring
 

So what was the base measurement, and the pegged measurement voltages???

Re: part throttle sputtering and backfiring
 

base was about .60v pegged was 4.10v. I didn't check resistance since the voltage checked out within spec. should I just to cover all bases? I don't have any of the previous symptoms

Re: part throttle sputtering and backfiring
 

Probably not necessary to check resistance if you got those voltages. ECM should recalibrate after a few Closed Loop cycles. DO remember it, just in case there...

Re: part throttle sputtering and backfiring
 

Hmmm.... Still acting up, although not as bad, I guess that wasn't the entire problem. It only does it on the highway, sustained speeds over about 55 or so seems like the magic number when it suddenly starts driving like crap. The MIL flickers on once in a while but never stores any codes. This is driving me nuts, it's barely driveable on the highway. I have no clue where else to look at this point.

Re: part throttle sputtering and backfiring
 

If SES light flickers, you should have at LEAST an H History DTC.

I think you should check again for this...

If nothing still, go to a shop and get a datalog scan printed out. You might have to ante up a few $, but you need that info.

Re: part throttle sputtering and backfiring
 

Haven't been to a shop yet but I plugged the EGR line after reading that the ECM does periodic checks of it at cruising speed and it seems to have fixed it. I may just keep it that way as long as it still doesn't throw any codes and goes into closed loop. Are there any negative effects of plugging the EGR vacuum? I'm guessing the valve itself was bad anyway so I Can't see how it could hurt anything worse.

Re: part throttle sputtering and backfiring
 

No exhaust into the intake allows higher burn temps. This = more NOx's, and emissions test could be a problem.

If it is, you'll have to fix it then, and no telling how long it could take to diagnose. Do it now, or do it later..........

Re: part throttle sputtering and backfiring
 

I'm not worried about emmisions just yet, I still want to get the PROM tuned to emulate the l69 i put in last year before I even begin to make everything cherry. PLus I need to replace the cat the PO gutted. But if plugging the EGR is a temporary band-aid with no ill effects I'll keep it that way for now.

Re: part throttle sputtering and backfiring
 

Ok now i'm really confused, I've never seen a vehicle do this before. I thought everything was fine, my MPG went through the roof, and then I took another trip on the highway. Now I barely get any bogging and stuttering, it just shuts off on me. Here's the weird part. I was coasting onto the shoulder to reset the ECM and get going again, when the engine started back up on it's own! it was definitely off, no power steering or brakes, and suddenly it came back to life of it's own volition and continued to drive another 3 miles before it did the exact same thing, until finally it stalled at a light getting off the highway and refused to start. So I jump out, disconnect the negative battery terminal and unplug the TPS like i did the other 5 times it died, and still it wouldn't start no matter what i did until it just sat there for about 15 minutes. Then it fired right away and purred like a kitten all the way home like normal. Any ideas from anyone are welcome, I'm taking it to the shop thursday but i'd really rather do this myself so anything I can look into would be appreciated.

Re: part throttle sputtering and backfiring
 

Look up how to check the injectors for the right resistance values.
The PO gutted the cat -> perhaps it died due to excessive unburnt fuel leaking from some of the injectors.
Suddenly dying off -> had that while my injectors were shot, but I still had my cat with its bowels inside of it. It was damaged, so the exhaust had no where to go. Gave it gas and the engine shut off.
Engine restarting -> well, that sounds like dieseling. Unburnt fuel igniting in the compression chambers. I saw something about that in the service manual a while ago.

Edit:
Found the part of the service manual describing the required checking procedures for dieseling.
HTH!

Re: part throttle sputtering and backfiring
 

Here's the other two pics.

Re: part throttle sputtering and backfiring
 

Hmmm.. I will chase this, although it doesn't seem to be dieseling, it just shuts off and since it's still in gear and moving it starts back up? I've never heard of it but after searching it seems to happen. Testing that should rule out fuel system either way so thank you. I'm still just hoping and praying after I get some data logging done tomorrow that it's just a sensor, it still has only been symptomatic when driven at highway speeds after it warms up and goes into closed loop, otherwise it runs like butter.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Well, I finally got a DTC to stick. Code 42. Happened at the same damn light I stalled at last night, this time it kept runing, very poorly, and putted and backfired horribly the last 1/2 mile home.. Anyone have the procedure to chase this down? I can't find it in my service manual.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

I thought of what you wrote... still in gear and so on... but you've got an auto trans, so: naaah... ;)

Perhaps this helps?
http://www.justanswer.com/pontiac/1m...-know-fix.html

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Are you using Chilton's / Haynes / Clymer's? Or FSM?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

stay away from that light....

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Have you replaced the ignition module. My car just randomly started sputtering backfiring and acting dumb on acceleration. Only did it once had a friend scan it no codes couple days went by same thing happened it went away checked again no codes. My friend who's a mechanic that scanned it suggested a ignition module. Put a module in and that has been 6-7 years with no issues. Just thought I'd throw that out there.


Edit: I reread your post sounds identical to what mine did. Barely touch the throttle it was fine after that pop bang to the moon lol.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

I have the fsm and chased that code 42 up and down the trouble tree twice, all pointed to the ecm being faulty, which it was especially when I notices all the start up system checks being performed again when I replaced it. It ran like normal for two 40 mile trips down the highway, its trouble spot. Then today it did the same **** and wouldn't start for twenty minutes, and I had to floor it just to go 10mph until it dies again in a quarter mile. I noticed my distribur was loose enough to turn by hand with a little effort. Could that cause a false 42? Like it's off and won't advance properly when in closed loop?or maybe even vats? It gets bad resistance readings and shits down the ignition system? I dam definitely smell the fuel when it dies and I try to crank it so that's not the problem.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

I know I'm not responding to everyone sonce im on my cell buti am looking at your links and trying the ideas out. If I can't figure this out I'm gonna be forced to sell it at a great loss to finance agaimst my willits the only car we have and we gotta get to work. We simply don't have shop money so it's gonna have to go and be replaced with 500 dollar Honda shitbox id I can't track this. I have one more chance before it has to go, and the ignition module sounds very plausible.. its definitely running onball cylinders despite the horrible lack of power I had earlier, engine note was uniform it just wouldn't accelerate...

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Try the module20 bucks and you'll know and if the distributor is loose time it and tighten it down.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

What he said.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Any new updates ravage?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

I'm gonna look into the icm tomorrow and see what happens, sounds fairly likely that's the culprit at this point

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

You could attach a normal timing gun and look whether the pulses come in regular intervals.
If not, ICM fried.
That's how I saw that mine was definitely dying.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Man it's one thing after another with this thing. I replaced the ignition module and it fixed that problem, but now i can't quite get it timed right and I don't have a light. It idles way to low no matter where I set it and stalls in gear, then I get a real slow crank if I try and start it right away. The starter was brand new a year ago, but could it be going bad from all the constant cranking i've been doing to it over the last 2 weeks? noticed my lights dimmed out real bad after the last stall, like the battery connection was loose and it wasnt. then everything brightened up and it cranked normally again. Maybe I shorted something out replacing the ICM?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Is a timing check called for in the diagnostic procedure? I venture not...
----------------------------------------------------------------

Post results of each point in the test procedure.

You write them out, and you think differently about each step, and results. Trust me.

Teacher OUT!!!!!!

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Ok fair enough. Well since I ruled out the ECM by replacing it, skipped that part of the diag since nothing crosses over. I wasn't getting the resistance switch when ohming the ignition module so ireplaced it and drove it with no problems, definitely more power, which I Seem to be getting back eveytime I replace en elsectrical component. The problem is the timing off ( i rechecked the dizzy and tightened it) and I can't get it back no matter what. I'll get a light on it tomorrow but it barealy moved when I bumped it and no matter what I do it still stalls. IF I had it that close where I can't hear a misfire but it still runs fine it shouldn't stall especially with no ping unless something else is wrong, correct?

Edit: I'm just inferring, the dim lights and slow crank were cause for concern but I sfeel like if I somehow have the timing way off may cause that.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

When your car is at operating temperature, check whether the carpet under the passenger's seat is hotter than usual.
Perhaps your injectors have died -> fuel ignites in the cat, destroys it and then the exhaust can't go anywhere and the engine stalls when you accelerate.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Check your charging system?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Dim lights CAN be caused by bad ground [harness] connections. Which can cause MANY other problems...

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

I'm getting a timing light today, bit the thought did crossmy mind that if I do in fact have an l69, and put my tbi on it, that I may need to time it differently should I just use the normal tbi method?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Ok I think I have this about dialed in. I tried setting the base timing to 6* like everyone seems to like, but it just wouldn't idle in gear, although throttle response and acceleration were phenonemal to what I'm used to. So i set it to 0* as per my hood sticker even though it's not the stock engine, it seems to like it the best. It seems to idle really low in gear, but it's pretty smooth, it just seems like it's always on the verge on stalling, hasn't done it though, maybe I"m just used to my old choppy idle and this is correct, my tach has the infamous R4 resistor out so it's no use. I get a check engine light that comes on at freeway speeds then goes off after a minute, still code 42, but I get no problems or change in performance, so i'm hoping it's just stored from before still. I also get code 13, which I believe is a rich condition? These codes seem to go hand in hand from I can see searching. Maybe I still have a wonky sensor? O2 maybe? Seeing as my old ECM was bad maybe this has been going on an dit just never picked up on it? IT took the damn thing a week of stalling and running like crap to even throw the original 42 code. I tried clicking on some links to chase the 13 but they were very old and all dead.And yes I DID reconnect the EST plug.

After more research it appears most people with a 13 get poor performance. My car hasn't run better since i replaced the ECM and ignition module. To the point where it chirps the tires if i'm not careful, and I also don't notice any loss of MPG. And the tire chirping is a bit impressive to me, i have 275's on the back and I used to only be able to barely spin them if I was turning an ddamn near floored it. I did notice I kept getting smoke out the exhaust when making timing adjustments, that usually only happens when I start it after it sat for a while from the valve seals. Maybe i just need to reset the ECM again for shits ang giggles?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Ok this is my last post on this subject, you have all been extremely helpful in your advice (and kept me from having to sell it to pay rent in lieu of shop fees). I also read that an upstream exhaust leak can fool the sensor and throw a false code, or actually just run lean and cause it. Well, I seafoamed my oil, tank and induction system (through the brake booster, I know it isn't ideal but it does the job) and when I dumped the last bit in to stall it and let it sit I noticed there was smoke coming from my drivers side exhaust manifold. Could my head/manifold be cracked or warped causing a leak? I replaced the gaskets when I did the swap exactly a year ago and I never hear that engine knock noise that usually accompanies a leak there. but obviously something was escaping there. Either way, I'm replacing the 02 since it's only 20 bucks and much cheaper than the alternative. Like I mentioned before I have no loss in performance, quite the opposite, so I"m still hoping this is a false code but just to be thorough what else should I be checking? The TPS was already replaced and tested as good. I only get about 15 MPG as it is, I really can't aford to be diving open loop all the time.. Again, you guys all saved my *** and I can't thank you enough so this is my last question on this topic.

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Replaced the 02 sensor, cleared all codes, code 13 still pops up.. Checked the sensor and it is swinging the readings perfectly within range now so it isn't bad.. Already have a new TPS... what could possibly be wrong??

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Have you done any research on that oxygen sensor? My buddy has a jeep and says ONLY THE FACTORY oxygen sensor will work. He bought some otherwise reputable aftermarket brand for it and it ran like poop. Paid a ton of money to a Jeep dealership to get a factory replacement one and it ran fine. Apparently those Renix jeep computers are SUPER picky about oxygen sensors.

You also say you tested what the O2 sensor readings are and they're good, so maybe there's a short in the wire. Can you see where that wire goes and measure it where it hits the ECM?

Re: part throttle sputtering and backfiring *UPDATE* Code 42??
 

Yeah all tests lead to a break in the wire. Would I just be able to cut the wire after the connector (or before? got some PB blaster in the connector getting the old one out, not sure on its condition) and at the ECM and splice a new one in completely? Or would I have to run a new ground as well? Can only find one wire and no ground so I'm assuming it grounds in the ECM?