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| Frustrating Backfire in T-Body on Rebuild; Backfire | |
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| Tweet Topic Started: Mar 15 2015, 09:59 PM (1,258 Views) | |
| CaptainMetro | Mar 15 2015, 09:59 PM Post #1 |
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After finally finishing the rebuild for my 94 XFI, I installed it over the weekend, it started and idled ok. But when opening the throttle it would stumble and violently backfire through the throttle body, and I couldn't run it above 900 RPM, it would just bog down and POP POP BBBLAP BBBLAP! So, I checked: cam timing fuel pressure Removed old gas and added 3 gallons of premium compression: OK plugs: black from spraying carb spray for possible lean issue, OK removed lower exhaust pipe for possible clogged cat no DTCs found vacuum leak (fixed but not the problem) all grounds clean and shiny all sensors connected spark timing @ 10 BTDC checked TBI spray pattern: OK different spark plug wires and CAP/ROTOR opened up ECM and looked for burnt spots: none The ECM could have been the problem, but nothing definitive At this point I was really concerned that I had botched the rebuild, but it didn't make sense since compression was good. Because the leads for my Vantage are bad, my measurement capabilities are limited until Monday, if it weren't for that I probably could have watched the CMP signal fade out at open throttle. I was going to hook up the timing light again to check if spark fell off when revving but I had another distributor on the bench so I put it in, and to my surprise and glee it purred like a kitten and revs up quite nicely. Now I have to fix the crank seal dumping oil (not sure why a brand new seal would blow, the crank bearings are nice and tight) but after that ordeal it's not such a hassle.
Edited by CaptainMetro, Mar 15 2015, 09:59 PM.
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| GeoStalker | Mar 15 2015, 10:03 PM Post #2 |
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"Chicks dig me and guys think I'm cool."
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Probably nothing to do with it, but did you burp the radiator system? |
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| CaptainMetro | Mar 15 2015, 10:13 PM Post #3 |
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I used an Airlift when I filled the cooling system. |
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| 91 ragtop | Mar 15 2015, 10:18 PM Post #4 |
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What all did you do to the engine in the rebuild process ? Ken......... |
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| CaptainMetro | Mar 15 2015, 10:20 PM Post #5 |
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Turned crank Resized rods Honed cylinders New valves (stainless exhaust) New lifters New exhaust guides New pistons/rings Planed head surface Edited by CaptainMetro, Mar 15 2015, 10:40 PM.
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| oregon250exc | Mar 15 2015, 10:23 PM Post #6 |
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New Member
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What in the distributor is there to go bad? I know the cam shaft position sensor is in there but if that was bad it would have thrown a code? I only ask because my car is doing the same thing. |
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| freegeo | Mar 15 2015, 10:39 PM Post #7 |
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Did the engine run ok before the rebuild? What was done to the lifters during the rebuild? Have you tried to retard the timing back to 5 BTDC and see if it will help? |
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| CaptainMetro | Mar 15 2015, 10:40 PM Post #8 |
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I bought the car without a running engine. I used new lifters, the other distributor did the trick. Edited by CaptainMetro, Mar 15 2015, 10:58 PM.
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| Hanuman | Mar 16 2015, 04:10 AM Post #9 |
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"The Almighty Grounds Cleaner"
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is there grease inside a lifterholding a intake valve open? mechanicaly the spark cannot occure early enough for a intake back fire without the valve being held open. the ecm also cant retard the timing this far (not that it matters, the distributor wont be near acontact this early. valve timing would need to be at least 2 teeth retarded. go back to your lifters. |
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| Car Nut | Mar 16 2015, 05:29 AM Post #10 |
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People, CM clearly states in post 1 & 8 that the car is healed."The other distributor did the trick". He replaced the distributor & it purred like a kitten. I was also thinking lifters until I saw it was running ok now.
Edited by Car Nut, Mar 16 2015, 05:32 AM.
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| Hanuman | Mar 16 2015, 12:55 PM Post #11 |
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"The Almighty Grounds Cleaner"
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i noticed that, but the time stamps for his edits....distributor was mentioned in the first post.....time stamped 1hour 40 minutes or so before post #8. im sure he will reply and we can find out for sure |
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| CaptainMetro | Mar 17 2015, 01:54 AM Post #12 |
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The edit on the first post was the new lifters part. |
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| Car Nut | Mar 17 2015, 08:49 AM Post #13 |
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Glad we got that cleared up.
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| Hanuman | Mar 17 2015, 02:01 PM Post #14 |
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"The Almighty Grounds Cleaner"
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gla we could help
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| CaptainMetro | Mar 18 2015, 01:33 AM Post #15 |
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Yes, well not directly but your numerous posts about clean grounds caused me to add it to my checklist. |
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Welcome to the all new Geo Metro Forum. We hope you enjoy your visit.

Because the leads for my Vantage are bad, my measurement capabilities are limited until Monday, if it weren't for that I probably could have watched the CMP signal fade out at open throttle. I was going to hook up the timing light again to check if spark fell off when revving but I had another distributor on the bench so I put it in, and to my surprise and glee it purred like a kitten and revs up quite nicely. Now I have to fix the crank seal dumping oil (not sure why a brand new seal would blow, the crank bearings are nice and tight) but after that ordeal it's not such a hassle.






![]](http://z3.ifrm.com/static/1/pip_r.png)
gla we could help
9:29 AM Jul 11