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Old 05-10-2009, 09:00 PM
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383 stroker pops and backfires

New rebuild

383 stroker
3.75 stoke scat 9000 crank
5.7 scat 4340 rods
claimer flat top, 2 valve relief +5.00 cc
brodix -8 pro aluminum heads 2.02, 1.60
10.5.1 compression ratio
pro comp full roller shaft rocker arms
edelbrock performer intake w/ egr
stock THROTTLE BODY
dragon fire distributor w/ stock coil (knock of msd)

Problem: Engine starts up and idles fast, around 2,000 rpm with spark advance plugged in, without it plugged in idles around 1,100 rpm. Engine backfires and pops through the throttle body. I adjusted the valve and timing over and over again, and yes i unplugged the spark advance when setting timing. I have a Holley 670 cfm throttle body to go in place of the stock throttle body but kind of wanted to get the engine running right before i swapped it out. I have no problem doing the swap if that is what is affecting it, the only concern i have with the throttle body is it doesn't have provisions for an idle air control, kind of curious if this will affect it besides the idle. Sorry for the rambling but kind of irritated at the damned thing and need to pick brains. Thanks a lot

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Old 05-10-2009, 09:38 PM
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Your 'popping' back through the throttle body indicates a 'timing' miss(cross)-fire. This can also be caused by a extremely lean condition. It almost sounds like you are 180 degrees out with your distributor, unless you have done like I did once, and wired it in a reverse rotation. I have also seen a spark crossover when the plug wires are zip-tied together.

I have also seen the wrong throttle body gasket leak, causing it to run lean. Your oxygen sensor could be out of range, causing the ecu to run it too lean.

If you have an EGR valve, pull it, and look for it being stuck open by some carbon. Inspect the spacer plate(if equipped), it could be warped.

Check your fuel pressure, it should be between 9-13 PSI.

There also could be a throttle body/air cleaner adapter with a tube assembly that hooks to the rear of the left side valve cover. With out this hooked up your idle will jump up.
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Old 05-11-2009, 05:02 PM
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Quote:
Originally Posted by crussell85
New rebuild

383 stroker
3.75 stoke scat 9000 crank
5.7 scat 4340 rods
claimer flat top, 2 valve relief +5.00 cc
brodix -8 pro aluminum heads 2.02, 1.60
10.5.1 compression ratio
pro comp full roller shaft rocker arms
edelbrock performer intake w/ egr
stock THROTTLE BODY
dragon fire distributor w/ stock coil (knock of msd)

Problem: Engine starts up and idles fast, around 2,000 rpm with spark advance plugged in, without it plugged in idles around 1,100 rpm. Engine backfires and pops through the throttle body. I adjusted the valve and timing over and over again, and yes i unplugged the spark advance when setting timing. I have a Holley 670 cfm throttle body to go in place of the stock throttle body but kind of wanted to get the engine running right before i swapped it out. I have no problem doing the swap if that is what is affecting it, the only concern i have with the throttle body is it doesn't have provisions for an idle air control, kind of curious if this will affect it besides the idle. Sorry for the rambling but kind of irritated at the damned thing and need to pick brains. Thanks a lot
The computer is lost, the changes you made are off the map, the computer has no idea what to do as the sensor input values do not match the program.

This is the down side of MAP sensed injection systems is that they haven't a sufficient range of learning to deal with more than very modest changes. The risk is you've got to define the engine and vehicle to a purveyor of reprogrammed chips well enough that the new chip comes withing +- 5% of dialing it in. You'll have to also add an adjustable regulator to dial in the new chip. Try some of these folks:

http://www.fastchip.com/

http://www.tbichips.com/

http://www.hypertech-inc.com/

http://www.superchips.com/

http://www.tpis.com/

This takes more than so called performance chips, this will have to be carefully reprogrammed.

Bogie
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Old 05-11-2009, 05:12 PM
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What kind of vehicle is it in and does it have a stock ECM.
I would put a vacuum gauge on it and see what the reading is and see if it is steady.
As suggested above also check to see the firing order is correct, pay special attention to #5 and # 7 as they are next to each other on the engine and the cap.

The distributor is most likely close as it does run, have you checked the timing. If you are checking it while the engine is at 1100 or 1200 rpm the reading is not what the at idle reading would be.

My gut says vacuum leak
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Old 05-11-2009, 10:37 PM
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the engine is in a 1993 Chevrolet k1500 z71. If it was 180 degrees out it wouldn't even run would it. I believe the distributor is set in the engine right, I just don't think the timing is set right with the engine at 1100 rpm. I have an egr block off plate on the intake right now because no parts store carry's an egr valve to fit the intake because it is different than the stock egr valve. The adapter plate that i have on the intake doesn't have two round holes in it is has one oval slot across the plate, i have the
Trans-Dapt Performance Products 2211 adapter plate bought from www.summitracing.com

i have the hole in the back of the air cleaner adapter that goes into the valve cover blocked off because the valve covers i have on the engine doesn't have the provisions for that. I had this engine in another vehicle with stock 882 heads and the stock tbi intake and didn't have a problem with it, it was in an 1989 Chevrolet k1500, the only 2 things i changed was the intake and the heads since it was in the other vehicle.
I am running the stock ecm but I was told that the ecm would adapt to the engine over time. That the engine would maintain the 14:1 air fuel ratio, but maybe not. I have been over and checked for vacuum leaks and i haven't found anything. thanks for the advice guys
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Old 05-11-2009, 10:59 PM
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One suggestion; try a different timing light.
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Old 05-12-2009, 06:14 AM
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Quote:
Originally Posted by crussell85
the engine is in a 1993 Chevrolet k1500 z71. If it was 180 degrees out it wouldn't even run would it. I believe the distributor is set in the engine right, I just don't think the timing is set right with the engine at 1100 rpm. I have an egr block off plate on the intake right now because no parts store carry's an egr valve to fit the intake because it is different than the stock egr valve. The adapter plate that i have on the intake doesn't have two round holes in it is has one oval slot across the plate, i have the
Trans-Dapt Performance Products 2211 adapter plate bought from www.summitracing.com

i have the hole in the back of the air cleaner adapter that goes into the valve cover blocked off because the valve covers i have on the engine doesn't have the provisions for that. I had this engine in another vehicle with stock 882 heads and the stock tbi intake and didn't have a problem with it, it was in an 1989 Chevrolet k1500, the only 2 things i changed was the intake and the heads since it was in the other vehicle.
I am running the stock ecm but I was told that the ecm would adapt to the engine over time. That the engine would maintain the 14:1 air fuel ratio, but maybe not. I have been over and checked for vacuum leaks and i haven't found anything. thanks for the advice guys
Check it with a vacuum gauge, it can tell a lot about an engine. You are correct it will not run 180 out. In a 93 the ECM does control a lot of the engine controls, on the older vehicles the ECM didnt do to much and most cars would run without it connected.

You need to check the basics first before you go re-programming or changing chips in the ecm. Vacuum and timing are very important. Make sure you tripple check the firing order, it is real easy to make a mistake on 5 and 7 and it will still run with them reversed just not well
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Old 05-12-2009, 05:04 PM
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what am i supposed to check with a vaccum guage? what would the affect be if i don't have the idle air control valve plugged in. I have a holley 670 cfm throttle body to put on the engine after i get it running right but it don't have the provisions for an idle air control.

The Rocker Arms: I have shaft mount rocker arms on the engine that adjust off the pushrod, what would be the best way to adjust these because I can't do it with the engine running like you would with the stud mounts.

Sorry guys I work out of town during the week and am home on the weekends so i won't have results until the weekend, just thought I would pick brains during the week. Thanks guys
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Old 05-12-2009, 05:31 PM
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Quote:
Originally Posted by crussell85
what am i supposed to check with a vaccum guage? what would the affect be if i don't have the idle air control valve plugged in. I have a holley 670 cfm throttle body to put on the engine after i get it running right but it don't have the provisions for an idle air control.

The Rocker Arms: I have shaft mount rocker arms on the engine that adjust off the pushrod, what would be the best way to adjust these because I can't do it with the engine running like you would with the stud mounts.

Sorry guys I work out of town during the week and am home on the weekends so i won't have results until the weekend, just thought I would pick brains during the week. Thanks guys
So I now understand you do not have the 670 cfm throttle body on it yet, and you have the original throttle body on it with the idle air control unplugged.

Plug in your idle air control, and turn your key on engine off, give it a couple minutes to extend all of the way, and unplug it. Then start it up, and see how it idles.
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Old 05-12-2009, 07:54 PM
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the stock throttle body is completely hooked up. The idle air control is plugged in and everything. But your answer answered my question. I never really thought about just unplugging the idle air control and seeing what it did after i get it running right. But everything is hooked up right now.
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Old 05-12-2009, 08:13 PM
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You are going to run the 670 cfm throttle body, with no idle air control. If that procedure does not idle it back down plug it somehow. Your idle air control could be wired different, or just stuck open.

Just a thought.
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Old 05-13-2009, 06:11 AM
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Quote:
Originally Posted by crussell85
what am i supposed to check with a vaccum guage? what would the affect be if i don't have the idle air control valve plugged in. I have a holley 670 cfm throttle body to put on the engine after i get it running right but it don't have the provisions for an idle air control.

The Rocker Arms: I have shaft mount rocker arms on the engine that adjust off the pushrod, what would be the best way to adjust these because I can't do it with the engine running like you would with the stud mounts.

Sorry guys I work out of town during the week and am home on the weekends so i won't have results until the weekend, just thought I would pick brains during the week. Thanks guys
The vacuum gauge will tell you if you have a leak. Vacuum leaks are the most common cause of runaway idle and will also cause popping. The IAC only effects idle and generally will not cause popping at speed.
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Old 05-13-2009, 04:09 PM
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i am glad i decided to go further than my brain on this problem because i am thinking it is probably a vaccum leak somewhere and I would have never thought about that. I don't mean to get off subject here (but its my post i can do whatever right? LOL) My vacuum for my brakes, on the tbi manifold the vacuum for the brakes was drawn just below the throttle body, i don't have that port on my edelbrock manifold, where do i draw the vacuum for them at. Would i draw it off the throttle body or draw it right from the manifold. Thanks

Last edited by crussell85; 05-13-2009 at 04:15 PM.
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Old 05-13-2009, 04:57 PM
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Off of the throttle body, if you run it from a port on a manifold runner, and the power booster diaphragm goes bad, it will lean out that cylinder instead of equally leaning out the whole engine.
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Old 05-13-2009, 07:40 PM
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OK, thanks a lot man, can i put a tee on the one that the PVC valve goes to because that is the biggest vacuum port on the throttle body. I don't know if this would effect the function of the PVC valve.
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