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Ok put new set of gt40 heads on my car after breaking oil pump shaft, old heads valve spring retainer desinagrated locked up pump. So replaced with gt40 heads mild port and roller rockers.removed distributor of corse, re installed it now car is popping back thru exhaust and has no power buddy of mine is doing work he says its the injectors,but they were fine before. Is this a timing issue sure seems like it to me,but hes supposed to be the mechanic. Any ideas on what it might be???????? He said thers a couple ways to set timing???????
 

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timing could be off, you can check it with a timing light or by using a vacuum gauge. Light is the easiest way. Depending on how far the timing is off the spark will be coming too soon or too late. The injector timing will be the same, but the spark will not be set off at the right time.
 

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Injector timing changes with Spark timing.... Back firing usually occurs when the Spark timing and the Valve timing are not in sync.
 

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true, but on that head install there is no reason to mess with the timing chain. The popping could be detonation from the firing event happening too early or late. and when first cranking the engine determines base injector pulse width using the CMP and TPS and MAP, you could have the timing advanced or retarded and the injectors will fire where the PCM has it set from the factory.
 

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true, but on that head install there is no reason to mess with the timing chain. The popping could be detonation from the firing event happening too early or late.
Read my first post, it stated just what you did in the bold writing. You said the injector pulse stays the same, while Spark timing changes, So I commented that, that is false. The injectors and Spark get the signal from the PIP signal, so if they get the signal form the same spot, how can they be off?:scratchchin Unless somethings faulty in the ECM itself.





Who said anything about a Timing Chain?:headscratch::headscratch:
 

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Injector timing changes with Spark timing.... Back firing usually occurs when the Spark timing and the Valve timing are not in sync.


Jumped timing chain would cause this, thats why i said it. and a bad CMP. I see what your sayin about the PIP. I just couldnt explain it right. PIP tells the PCM when to pusle the injector, injector on time is determined by the sensors. The only exception to the PIP setting the pulse width would be at WOT. Then the injector just stays on, no time to pulse.
 

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true, but on that head install there is no reason to mess with the timing chain. The popping could be detonation from the firing event happening too early or late. and when first cranking the engine determines base injector pulse width using the CMP and TPS and MAP, you could have the timing advanced or retarded and the injectors will fire where the PCM has it set from the factory.
You said not to mess with the timing chain in the above post, but before that, it was not mentioned by you or me.:headscratch:
 

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Back firing usually occurs when the Spark timing and the Valve timing are not in sync.


You said the above quote on your second post. all in trying to get across, is for the spark timing to be off from the valve timing the timing chain would have had to of been messed with. And on the head install there is no reason to mess with the timing chain. So if the timing chain was left as it was before the repair, then the popping is from advanced or retarded ignition timing. Not valve timing.
 

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If the dizzy is not dropped in correctly, the Spark timing can be off from the valve timing, even with a correctly setup timing chain. Drop one in a few tooths off and see what happens. Spark timing and valve timing are different, but need to work together properly. Hence the 180° off symptom:bigthumbsup
 

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oh ****, the ol' 180, good call. I've never had this problem with a 5.0. I didnt know it would still run at 180 flip. There is other motors that will not run or just start and die. Thanks for the info!!!
 

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It wont run 180° off, its just an example of how the Spark and valve timing are not in sync as I stated earlier. For simplicity, just call it Ignition timing, you get the same thing by rotating the dizzy to a certain extent, but if your too far off, you cant turn the dizzy far enough to correct it.

My spark and valve timing post wasnt meant as to mess with the timing chain, just as they are working at the wrong time.:bigthumbsup

We were on the same page, just with different explainations, which led to different thoughts.
 

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Ya, i got what your saying. Well I think the original poster should understand how the system works, even though the thread looks like a dumpster fire.
 
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