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Post Info TOPIC: Help diagnose my engine
JC2+2


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Help diagnose my engine
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I have seen the pickup coil wires break without breaking the insulation and the vacume advance will pull them apart. The engine dies for a split second and then the wires touch and then not and so on. Causing a crazy bucking. Disconnect the vacume advance and drive it. If the bucking is cured, change the pickup. Good luck.



-- Edited by jc on Wednesday 11th of July 2012 10:35:22 PM

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pontorquer


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Ok Thanks guys ! I have a spare fuel pump that I will try and will also try disconnecting the vacuum advance to see what happens ?

Slowly everything is fine ...



-- Edited by pontorquer on Wednesday 11th of July 2012 10:31:39 PM

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pontorquer


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First the good news : I'm gonna be a grand papa ! My 21 yo son and girlfriend are expecting a baby, I found out last night ... Secondly I got my 75 Grand Am back on the road today ! I worked on it for the past couple of days, I replaced the accelaretor pump and inspected/cleaned the guts of this 75 Qjet, sure helped. Also, I replaced the HEI coil in my distributor. The problem is when I drive on the highway at let say 60 mph and stump on it, the engine bucks violently and I get a backfire through the back, It started doing it at the end of last summer ... To me it's like the ignition is not keeping up with the higher revs, so not burning the fuel properly in the cylinders. The engine is a Pontiac 400, could it be the vacuum advance or module, maybe the pickup coil ??? Help Please  



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gparis7


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That or maybe not enough fuel delivery - too lean, fuel pump, etc .



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4SPEED427


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Do you not have another car you can swap the distributor from? That would eliminate that possibility (or confirm that is the problem)

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pontorquer


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Guess I could do that as I got 2 other spare HEI distributors ... lol. First I have to try the plug the advance trick just to satisfy my curiosity ... I know, Process of elimination with these old cars ...



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pontorquer


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Tonight I plugged the vacuum source for my distributor advance and put the timing light on the balancer just for the heck of it, at first it was pretty steady at 8 BTDC where I had it set last summer then, all of the sudden the mark fell down at least 2 " off the timing mark tab BTDC so there is definitatly something wrong with the distributor, the engine had this rubbing sound like when it's off timing and yes the retaining bolt on the distributor is real good and tight. Could it be a bad distributer shaft ? By the way what's this rubbing sound when the engine's out of time ?



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rabbit64cs


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how much slop is in your timing chain?  take off the distributer cap, watch the rotor and rotate the crank by hand, Clock wise and counter clock wise..

a sloppy chain should show this way, if there is a lag when you rotate...



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later...rog

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pontorquer


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Hmmmm ! Sounds like a combination of worn out engine parts, maybe it's time to yank this tired engine and install the 455 ... I was hoping to drive it a little more and enjoy the summer cruise.  



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rabbit64cs


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I e also read that Chevy hei coils are not the same as Pontiac hei coils? They have differnent coloured wires, and will act sonny at higher rpms? Anyone????

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66 Beau


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HEI's are well known for sticky mechanical advances. Check to make sure the weights swing in and out easily and smoothly.

Your misfire/big then back fire on hard acceleration sounds like a leaning out problem. Is the new accelerator pump working properly? Is this happening when the big vacuum secondaries open up?

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pontorquer


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Started process of replacing my timing chain tonight and distributor ... I got everything off in a couple of hours without any issues, how lucky I was compare to Todd ie. no seized or broken bolts, the chain needed replacement, she's pretty loose about 1/2 inch play. Got to clean the cover and parts now soo many years of yucky oily grime, all automotive fluids where covering my hands, I love that dirty mechanic work ! lol 



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Canadian Poncho


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I'm glad to hear you didn't experience the grief I did!

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pontorquer


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Ok, today the car is back on the road ! I was gone on holiday for 3 weeks. So what I did to the engine : I replace the timing chain, the fuel pump, accelerator pump on the Qjet, distributor, bunch of vacuum hose, balancer, timed the engine and ajust the idle mixture screws with vacuum gauge got it up to 16. Then after all this was done I took it for a drive on the highway, floored it and still acted up around 80-90mph, heard backfire threw the exhaust so the only thing left I'm thinking is the carb, definatly fuel lean starvation ... 



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66 Beau


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Start checking fuel delivery system. Fuel pump, lines, filter (in-line and sintered), also check jets and float levels.

Actually, you've done a ton already with no success. Maybe it's time to do some diagnosis rather than just replacing stuff. Can you hook up an exhaust gas analyzer you can leave active while you take it for a drive?



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Beaumont4008


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Also check to see if you back barrel's air valve is opening. They can get sticky over time and not open. There is a small set screw that sets the spring pressure on the valve. You can set it to open earler or later depending on how much spring pressure you have.



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pontorquer


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Thanks guys, tonight I filled the beast up with 77 liters of mid grade gas and she was working alot better, I only put 20$ of gas twice prior to this,  tonight she worked alot better ... WOT at 90mph and no backfring :) but still not quick and peppy enough ... lol. It must have been old stale gas and stabil left in the tank after winter storage, doesn't take much to throw these old Qjets out of wack ...



-- Edited by pontorquer on Thursday 23rd of August 2012 10:36:26 PM

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66 Beau


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Gas today is horrible. It must be the ethanol that causes the gas to break down. I plan on leaving my vehicles (car, boat, motorbike, lawnmower etc) full of premium (with no ethanol) plus some Stabil. I had to strip carbs and fuel systems on the boat and motorbike this spring to get them to fire up. They still didn't run well until i got through a full tank of gas.

I should have thought to ask about the gas. Glad it's getting better!

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Keith Tedford


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I understand that Petro-Can Ultra 94 has no ethanol either.  True?  What ever, I use Shell premium in EVERYTHING.



-- Edited by Keith Tedford on Friday 24th of August 2012 09:50:16 PM

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Keith Tedford
pontorquer


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I read on other forums that stabil ain't that good either ? I stay away from Mohawk or Husky, they use alot of Ethanol crap ... Any good gas suggestion in Winnipeg MB ? Coop Ok ?



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Fake68


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The only fuel you can buy now without some amount of Ethanol blending is Shell Premium.

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Pontiacanada


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My gas never goes bad in under a year. I get 20 litres of high octane gas, then add octane boost, Stabil, lead additive, and gasline antifreeze. I shake it ... never stirred!biggrin



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