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Old 03-22-2012, 10:18 PM   #1
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92 Camaro RS - rpm's surging/loping

92 Camaro RS 3.1L V6, auto trans. When I start the car, the engines rpm's goes from 1000 to 4000 erratically. I can see this on the tach. It does not stop doing that until the engine stalls or is shut off. It backfires sometimes. I put a new gasket on the intake manifold. The battery was disconnected while it was being fixed. I did take the distributor out, and put it back in. I checked the timing. To me it appears to be ok. When I put a timing light on spark plug #1, I can see the timing mark on the scale, it bounces so I am unable to set it properly. But the timing mark is within the range it is supposed to be. Which I believe means that the distributor was put in correct. The car also has a brand new TPS and vacuum lines. Please help, thanks.
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Old 03-22-2012, 10:25 PM   #2
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Re: 92 Camaro RS - rpm's surging/loping

Sounds like a huge vacuum leak. Is the PCV hose connected? How about the brake booster?
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Old 03-22-2012, 10:28 PM   #3
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Re: 92 Camaro RS - rpm's surging/loping

Yes to both of them. Where should I check the vacuum?
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Old 03-22-2012, 10:39 PM   #4
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Re: 92 Camaro RS - rpm's surging/loping

You can check vacuum at any manifold vacuum source. It won't tell us much though with the engine surging like that. Try instead to find a large leak somewhere in the intake. You can use brake cleaner, propane, or carb cleaner for this purpose. Be sure also to double check that the MAP sensor is connected properly.

Very low fuel pressure may also cause a symptom like this. Look at your injector spray pattern. It should be a pretty good cone shape. With a snap of the throttle, the cones should touch the walls of the throttle bores. If not, you may have a broken pressure regulator spring in the throttle body.
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87 IROC Z28, 355 TPI, 10.2:1, 6" rods, balanced, clearanced, TFS G2 heads fully ported, ZZX Cam, ported Superram base, large tube runners, 1 3/4 pri coated stainless short tube, 58mmTB on ported plenum, ram air, high flow air lid, 24lb bosch @ 70 psi, ACCEL DFI, MSD D6, funct hood louvers, etc. SSM SFCs, Hotchkis rear links& strt twr brace, Eibach Sportline, Koni Red S&S, PST bushings, Ed's 13" w/WW 4 piston calipers in front, LS1s in back. GTA seats, MOMO wheel, B&M Megashifter
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Old 03-22-2012, 11:28 PM   #5
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Re: 92 Camaro RS - rpm's surging/loping

Unable to see any difference with spraying break clean. The vacuum line that goes from the intake to the MAP sensor has a vacuum of 5. Then jumps to 20, then back to 5 and stays there. While the map sensor vacuum is off the rpm's settle. Also, if I take off the electrical connector (and put the vacuum back on the map sensor) on the map sensor, the rpm's settle. Not loping. There is backfiring through the exhaust on the passengers side. I adjusted the distributor, with not much change after removing the vacuum line or map electrical connector. The map sensor was replaced within the last 2 years.

Unable to check the injectors, as they are under the plenum.

Last edited by MI_AMOR_2010; 03-22-2012 at 11:34 PM.
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Old 03-23-2012, 12:23 AM   #6
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Re: 92 Camaro RS - rpm's surging/loping, still need help after 5 posts please

oops.. still need help tho
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Old 03-23-2012, 04:13 PM   #7
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Re: 92 Camaro RS - rpm's surging/loping, still need help after 5 posts please

Try using a vacuum pump to apply 18 inches of vacuum to the MAP sensor. See if the engine stabilizes. I want to know what integrator and block learn are doing on your car. You need a scan tool to view datastream. The exhaust firing is likely due to lean misfire.
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Old 03-23-2012, 04:23 PM   #8
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Re: 92 Camaro RS - rpm's surging/loping

http://www.youtube.com/watch?v=eywJZHHFkLI

Here is a video of the car. I don't have a vacuum pump... how much are they?
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Old 03-23-2012, 04:48 PM   #9
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Re: 92 Camaro RS - rpm's surging/loping

A cheap one from the parts store, like MITYVAC brand, is about $35. A scan tool like the SnapOn MT2500 is available used on craigslist for about $250 These old scan tools will always hold their value so you could always sell it for what you paid if you chose to.
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87 IROC Z28, 355 TPI, 10.2:1, 6" rods, balanced, clearanced, TFS G2 heads fully ported, ZZX Cam, ported Superram base, large tube runners, 1 3/4 pri coated stainless short tube, 58mmTB on ported plenum, ram air, high flow air lid, 24lb bosch @ 70 psi, ACCEL DFI, MSD D6, funct hood louvers, etc. SSM SFCs, Hotchkis rear links& strt twr brace, Eibach Sportline, Koni Red S&S, PST bushings, Ed's 13" w/WW 4 piston calipers in front, LS1s in back. GTA seats, MOMO wheel, B&M Megashifter
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Old 03-23-2012, 04:56 PM   #10
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Re: 92 Camaro RS - rpm's surging/loping

Are you able to look at the video? Not sure what you mean by "integrator and block learn." ECM? And I don't have a obd 1 scanner, just an obd 2.
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Old 03-23-2012, 07:51 PM   #11
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Re: 92 Camaro RS - rpm's surging/loping

Block learn and integrator are the ECM's fuel trims block learn is long term, integrator is short term. You can watch them with a scanner. Of course an OBDII scanner wont work on an OBDI system. I have not had a chance to watch the video yet.
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87 IROC Z28, 355 TPI, 10.2:1, 6" rods, balanced, clearanced, TFS G2 heads fully ported, ZZX Cam, ported Superram base, large tube runners, 1 3/4 pri coated stainless short tube, 58mmTB on ported plenum, ram air, high flow air lid, 24lb bosch @ 70 psi, ACCEL DFI, MSD D6, funct hood louvers, etc. SSM SFCs, Hotchkis rear links& strt twr brace, Eibach Sportline, Koni Red S&S, PST bushings, Ed's 13" w/WW 4 piston calipers in front, LS1s in back. GTA seats, MOMO wheel, B&M Megashifter
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Old 03-23-2012, 08:16 PM   #12
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Re: 92 Camaro RS - rpm's surging/loping

Just watched your video. One note on the EVAP canister vacuum, it is ported vacuum on that early system so it will not have vacuum at closed throttle. I also saw a puff of smoke from somewhere just behind the throttle body when the engine backfired. I am not convinced at all that the MAP sensor is causing your problem. I really didn't see much improvement from unplugging it. I am really thinking at this point that you have a huge unmetered air(vacuum) leak. You say that you just did the intake manifold gaskets did the engine surge like this before that? You may have a leak into the crankcase. You can test for this by removing the PCV valve from the valve cover and checking for vacuum at the open hole in the cover.
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87 IROC Z28, 355 TPI, 10.2:1, 6" rods, balanced, clearanced, TFS G2 heads fully ported, ZZX Cam, ported Superram base, large tube runners, 1 3/4 pri coated stainless short tube, 58mmTB on ported plenum, ram air, high flow air lid, 24lb bosch @ 70 psi, ACCEL DFI, MSD D6, funct hood louvers, etc. SSM SFCs, Hotchkis rear links& strt twr brace, Eibach Sportline, Koni Red S&S, PST bushings, Ed's 13" w/WW 4 piston calipers in front, LS1s in back. GTA seats, MOMO wheel, B&M Megashifter
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Old 03-24-2012, 06:59 PM   #13
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Re: 92 Camaro RS - rpm's surging/loping

found crack in upper plenum... Where can I get one?
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Old 03-27-2012, 06:44 PM   #14
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Re: 92 Camaro RS - rpm's surging/loping

There ya go. That must have been the vertical puff of smoke I saw when the engine backfired. Where to find a plenum? I would start by doing a parts request on the parts forum right here on TGO. Ive had excellent success when I used the "Parts Wanted". Option. If no luck, which would surprise me, then try a google search for used auto parts.
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87 IROC Z28, 355 TPI, 10.2:1, 6" rods, balanced, clearanced, TFS G2 heads fully ported, ZZX Cam, ported Superram base, large tube runners, 1 3/4 pri coated stainless short tube, 58mmTB on ported plenum, ram air, high flow air lid, 24lb bosch @ 70 psi, ACCEL DFI, MSD D6, funct hood louvers, etc. SSM SFCs, Hotchkis rear links& strt twr brace, Eibach Sportline, Koni Red S&S, PST bushings, Ed's 13" w/WW 4 piston calipers in front, LS1s in back. GTA seats, MOMO wheel, B&M Megashifter
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Old 03-28-2012, 06:05 PM   #15
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Re: 92 Camaro RS - rpm's surging/loping

One thing that I should mention, I see cracked plenums way too often on the 3.1 and 3.4 V6s. The cause of them cracking is over-tightening, misalignment of the gasket(the little alignment tabs need to be fully seated in the holes provided for them), or failure to follow the torque sequence.

Be sure when you tighten the fasteners that you use nothing larger than a 1/4 drive ratchet. Start with the middle bolt on either side and work your way out in a circular pattern. Turn each bolt only 1/2 turn each time. After all fasteners and the gasket is fully seated, torque the fasteners to 88in/lbs using a suitable torque wrench.
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87 IROC Z28, 355 TPI, 10.2:1, 6" rods, balanced, clearanced, TFS G2 heads fully ported, ZZX Cam, ported Superram base, large tube runners, 1 3/4 pri coated stainless short tube, 58mmTB on ported plenum, ram air, high flow air lid, 24lb bosch @ 70 psi, ACCEL DFI, MSD D6, funct hood louvers, etc. SSM SFCs, Hotchkis rear links& strt twr brace, Eibach Sportline, Koni Red S&S, PST bushings, Ed's 13" w/WW 4 piston calipers in front, LS1s in back. GTA seats, MOMO wheel, B&M Megashifter
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Old 02-25-2013, 07:16 PM   #16
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Re: 92 Camaro RS - rpm's surging/loping

I completely broke off the mounting tab on my plenum where the throttle body bolts up to. That was over a year ago. I JB welded the hell outta it and never looked back. If it's a small crack, it can be welded.
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Old 02-25-2013, 07:16 PM
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