Wiped Cam Lobe? What are my options? (Page 6/7) 82-T/A [At Work] JUN 07, 09:42 AM quote Originally posted by tnkgnr: Well - put a new camshaft and lifters in; Comp Cams 260H. Using a caliper on the old one, the lobes varied between 38mm and 40mm so it seems there was some wear. Car pulls even better than it did before on acceleration, but I still have the bucking issue when trying to maintain a constant speed Any ideas left out there? Hi! Hope I'm not too late... but wanted to make a few comments... 1 - OMG... "Antique" is that how old the Fiero is? I'm beside myself. 2 - Can we now confirm that the crank was not the concern? 3 - I don't know if this helps... but I had massive bucking one day with my Fiero, several years ago. I disconnected my MAP sensor, and the car was able to drive just fine. Acceleration wasn't too bad, but any time I tried to maintain speed, the car bucked like crazy. It just happened one day, and was really bad. I was able to get home by disconnecting my MAP sensor, and I ended up replacing it with a newer one: https://www.pontiacperforma...les/MAP_Upgrade.html I can't say if that will solve your problem, but that is exactly the same symptoms I had, and replacing the MAP sensor solved it. I seem to recall that the MAP was also oozing fluid ??? which I didn't even know was a thing... but it didn't look very good. tnkgnr JUN 07, 04:25 PM quote Originally posted by fieroguru: Sounds like you have a lean misfire on one cylinder. It will only show up at idle or cruise. It is small enough that the other cylinders are being commanded richer and compensating for the extra oxygen in the exhaust w/o tripping a check engine light. Likely causes: Partially clogged injector. Intake gasket leak letting making a single cylinder lean. Idle works well - only a cruise problem. I don't think there's a clogged injector though. This issue existed on a previous set of injectors and I have a whole new (unused) set in there now with the same issue. Is there a way to confirm that the injectors themselves are receiving the electrical pulses to fire? Maybe a bad wire somewhere? All the intake gaskets are new. tnkgnr JUN 07, 04:29 PM quote Originally posted by 82-T/A [At Work]: Hi! Hope I'm not too late... but wanted to make a few comments... 1 - OMG... "Antique" is that how old the Fiero is? I'm beside myself. 2 - Can we now confirm that the crank was not the concern? 3 - I don't know if this helps... but I had massive bucking one day with my Fiero, several years ago. I disconnected my MAP sensor, and the car was able to drive just fine. Acceleration wasn't too bad, but any time I tried to maintain speed, the car bucked like crazy. It just happened one day, and was really bad. I was able to get home by disconnecting my MAP sensor, and I ended up replacing it with a newer one: https://www.pontiacperforma...les/MAP_Upgrade.html I can't say if that will solve your problem, but that is exactly the same symptoms I had, and replacing the MAP sensor solved it. I seem to recall that the MAP was also oozing fluid ??? which I didn't even know was a thing... but it didn't look very good. 1 - Not only is it an antique - it's been one for over a decade now! 2 - What issues could I expect with the crankshaft? 3 - Yea, I tried disconnecting the MAP, still had the same issue. I tested my old one just fine with a vacuum pump but ended up ordering a new one just in case. No luck. 82-T/A [At Work] JUN 07, 08:31 PM quote Originally posted by tnkgnr: 1 - Not only is it an antique - it's been one for over a decade now! 2 - What issues could I expect with the crankshaft? 3 - Yea, I tried disconnecting the MAP, still had the same issue. I tested my old one just fine with a vacuum pump but ended up ordering a new one just in case. No luck. Geeze, that sucks... really thought that would work. Let me confirm some statements... It stumbles when you try to maintain speed, correct? Does it stumble on acceleration as well? Or only while maintaining speed? My first thought (since it's not the MAP), is some kind of fuel issue... Has it always done this since you've owned it, or is it something that just magically started one day? Another thing could be the gap of the spark plugs (.35 vs .45), but if you haven't changed them in a while, then likely not that either... and that's a long shot. tnkgnr JUN 07, 09:44 PM quote It stumbles when you try to maintain speed, correct? Correct - only when maintaining a speed; roughly in the 2k RPM area. quote Does it stumble on acceleration as well? Or only while maintaining speed? No, it accelerates great. Idles solid. Deceleration through the RPM range is fine. quote My first thought (since it's not the MAP), is some kind of fuel issue... Fuel pressure is good. Fuel pump is only a few months old. Filter is pretty young too. quote Has it always done this since you've owned it, or is it something that just magically started one day? Just showed up one day - magic! quote Another thing could be the gap of the spark plugs (.35 vs .45), but if you haven't changed them in a while, then likely not that either... and that's a long shot. Plugs are pretty new, gapped to .045 82-T/A [At Work] JUN 11, 09:38 AM quote Originally posted by tnkgnr: Plugs are pretty new, gapped to .045 Ugh... well, most of those responses sound good... so it sounds like at wide open throttle and decent throttle, it accelerates well... so there's no mechanical issues with things like the cam, or injectors, or something of that such. It seems like it's possibly a throttle problem. I didn't see in the other threads, but have you looked at the Throttle Position Sensor / TPS? Not a whole lot of help here: https://www.pontiacperforma...rticles/OSG/TPS.html but it does talk about some issues. With a functional TPS and a functional IAC (Idle Air Control) valve, the car will idle well, and accelerate well at WOT. But... as you know, the TPS is basically a pentameter... in 2005+ cars that use drive by wire, the pentameter is moved from the TPS to the gas pedal, and eliminates the throttle cable and instead controls a solenoid. Anyway, it's been over a decade (my Fiero is literally sitting in a storage unit where it's been for 12 years), but there is a little arm that needs to be adjusted on the TPS, which allows you to fine tune and adjust the TPS. At the same time... the TPS may be failing in that the sweep of the throttle is not providing the voltage it should in the lower RPMs. Since most of your driving is not wide open throttle, and most of your driving is going to be in the ~2000 rpm range... the contacts for the TPS will wear much more frequently in that range, which can often cause problems there. You could either try adjusting the little tab to increase or decrease the amount of throttle your TPS is reporting, or replace the TPS and see if that fixes the problem. :/ sorry I couldn't be of more help... but definitely interested in helping you get this fixed. tnkgnr JUN 11, 10:52 PM quote Originally posted by 82-T/A [At Work]: Ugh... well, most of those responses sound good... so it sounds like at wide open throttle and decent throttle, it accelerates well... so there's no mechanical issues with things like the cam, or injectors, or something of that such. It seems like it's possibly a throttle problem. I didn't see in the other threads, but have you looked at the Throttle Position Sensor / TPS? Not a whole lot of help here: https://www.pontiacperforma...rticles/OSG/TPS.html but it does talk about some issues. With a functional TPS and a functional IAC (Idle Air Control) valve, the car will idle well, and accelerate well at WOT. But... as you know, the TPS is basically a pentameter... in 2005+ cars that use drive by wire, the pentameter is moved from the TPS to the gas pedal, and eliminates the throttle cable and instead controls a solenoid. Anyway, it's been over a decade (my Fiero is literally sitting in a storage unit where it's been for 12 years), but there is a little arm that needs to be adjusted on the TPS, which allows you to fine tune and adjust the TPS. At the same time... the TPS may be failing in that the sweep of the throttle is not providing the voltage it should in the lower RPMs. Since most of your driving is not wide open throttle, and most of your driving is going to be in the ~2000 rpm range... the contacts for the TPS will wear much more frequently in that range, which can often cause problems there. You could either try adjusting the little tab to increase or decrease the amount of throttle your TPS is reporting, or replace the TPS and see if that fixes the problem. :/ sorry I couldn't be of more help... but definitely interested in helping you get this fixed. Really appreciate your interest in helping me get this fixed - I'm completely stumped... For the TPS, I did monitor the voltage through the sweep of throttle, and it looked good (both the voltage range and no hiccups in the area that would normally wear). Installed a new one anyways just in case. Didn't change anything. I don't think I've tried with it unplugged though, so I'll give that a run. For the throttle itself, it had probably been molested at some point, since the screw cap was missing. But I went through the procedure to ensure the proper adjustment (hopefully correctly). It idles at or a hair under 1k rpm. Perhaps one clue I should mention - the bucking doesn't happen for the first 2 or 3 minutes of driving. I've tried disconnecting the O-2 sensor to see if there was some sort of relationship there, but that was a dead end too. greenturnedblue JUN 15, 01:33 AM I recently replaced my oil pressure sender because it was reading erratically. Turns out it was still the original one and was completely corroded inside. While researching it I learnt the oil pressure sender also feeds the fuel pump in parallel with the fuel pump relay, in case the relay fails the fuel pump will still run off the oil pressure sender circuit. I mention this because my sender would read fine during the first few minutes of driving but after it got warmed up it would read far lower then the actual oil pressure (confirmed with mechanical gauge). Im not sure if this would even be possible but maybe your fuel pressure relay is dead and the fuel pump is being run solely off the oil pressure sender. After driving your car a few minutes your failing oil pressure sender starts reading abnormally and sends sporadic voltage to the fuel pump, leading to your jerking motion. But, this doesnt explain how your issue manifests only at constant speed, im not sure how the oil pressure sender even if it were failing could affect that. But, you could test if the fuel pump relay is working by listening for it clicking on when you turn the key to 'on' and the pump primes for 3 seconds. the relay is mounted at the top left of the firewall above the air filter. you could also just unplug the oil pressure sender, if the jerking persists it obviously isnt the sender. It only feeds the gauge so it wont effect anything wont even throw a CEL tnkgnr MAY 11, 07:41 PM Do I dare say I figured it out? Unplugged the tach filter after reading elsewhere that problems with it can result in "hiccups" and other issues. Drove it around and seems fine. I'm skeptical though - why would it have such a huge impact? My tachometer was working, so I dunno...but tentatively seems okay. Pic of my ride, cause I'm in love with this wrap job 82-T/A [At Work] MAY 12, 10:50 AM quote Originally posted by pmbrunelle: You're sure it's the cam lobe? Check the rocker arm pivot balls for wear, myself and another person have had trouble with the Comp Cams Magnum rocker arms. Old post PM... but the CompCams ones you're referring to, is that THESE rocker arms? https://www.fierostore.com/...0%20%20160&d=352&p=1 I have those too, and with my old engine, I started having issues. I was considering re-using these in my new 3.4, but now questioning if I should even bother. What kind of issues did you have? Were they seeing premature wear? Nothing re-adjusting the valve lash couldn't fix? Thanks!