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Old 07-17-2011, 08:05 PM   #1 (permalink)
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Question Sbc 350 with tbi conversion

Carberated chevy 350 , i machined a piEce of aluminum to except the tbi. All sensors are new wiring harness is new. Installed tbi ballencer and timing chain cover. But... When I time this bad boy with or without the computer timing advance wire hooked up I can't get it to do right. it will run at 0 degrees with a very rough and low idle. But as soon as u give it some gas it backfires through the intake. It seems to run best with the timing mark strait up. No where near the timing tab? It will rev up at this location. However if u hold the idle up to around 1500 rpm it will slowly lose all power. I have a Carter in line fuel pump that I bought from summit that's for a tbi conversion it's mounted 4 inches from the outlet in the fuel cells sump.with a glass inline filter infrOnt of the pump. . Questions are what's up with my timing issues and could I be running it out of fuel?
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Old 07-17-2011, 08:18 PM   #2 (permalink)
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read this in a different forum:
You guys might try to swap the two wires in the dizzy on the module from the pickup coil. I had this issue one time with an aftermarket pickup . Had to time it way too far advance . Once I reversed the wires the timing was set normally and ran good. Worth a try.

from: http://forum.ih8mud.com/hardcore-cor...-problems.html

not sure what a dizzy is or what plug they are talking about but my pickup coil is new from the local vato zone, has anyone else herd of such a thing?
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Old 07-18-2011, 07:11 AM   #3 (permalink)
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whats your fuel pressure? It sounds a little like your running out of fuel. Is there any mods done to the ecu? The pickup wires crossed could be your timing gremlin. The map sensor could be as well. It needs constant vacuum and weve had better luck mounting it higher than the vacuum source and somewhere dry. Someone correct me if I'm wrong but I think you should have around 20 psi or whatever vacuum at an idle. If you don't you've have a vacuum leak somewhere. If you can eliminate those I have some great write ups on my home computer about trouble shooting tbi I can pm them to you

good luck
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Old 07-18-2011, 07:13 AM   #4 (permalink)
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Originally Posted by Westtexasgearheadz View Post
Carberated chevy 350 , i machined a piEce of aluminum to except the tbi. All sensors are new wiring harness is new. Installed tbi ballencer and timing chain cover. But... When I time this bad boy with or without the computer timing advance wire hooked up I can't get it to do right. it will run at 0 degrees with a very rough and low idle. But as soon as u give it some gas it backfires through the intake. It seems to run best with the timing mark strait up. No where near the timing tab? It will rev up at this location. However if u hold the idle up to around 1500 rpm it will slowly lose all power. I have a Carter in line fuel pump that I bought from summit that's for a tbi conversion it's mounted 4 inches from the outlet in the fuel cells sump.with a glass inline filter infrOnt of the pump. . Questions are what's up with my timing issues and could I be running it out of fuel?
Really? You want to know if you could be running it out of fuel? How the hell do we know? Hook it up to a fuel pressure gauge and then come back and tell us.

As to the timing question, well, Have you checked to see if your engine is actually at TDC, when the balancer says it is? What heads are you running, What cam are you running? You can get away with small changes when swapping a TBI, but you have to know what you are starting with. The factory tune is set up for the tiny cam, with a wide LSA, and the 093 swirl port heads. Get too far away from stock specs, and yeah, I can see problems.
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Old 07-18-2011, 07:45 AM   #5 (permalink)
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Dizzy = Distributor

Timing chain could be stretched. Dizzy (Distributor) could be off by one tooth. Could have wrong damper/timing cover timing marker. Could have incorrect firing order (plug wires connected to wrong cylinders). Could have a malfunctioning knock sensor. Never heard of the ignitor wires being reversed, though.
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Old 07-18-2011, 07:52 AM   #6 (permalink)
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Picking up a inline pressure gauge hopefully today. ECM is stock and my map is mounted atleast 2 in higher than where it picks up. If the pick up wires are crossed which ones are we talking about, on the wiring harness or in side the distributor cap?

Dayhole
Running stock carbureted heads and cam with a tourquer 2 intake . And no offense but I have been doing research and buckin with this god forsaken motor for 2 years or more. Any ways the only mods it could possibly have is it's been bored .030 over. Also I think I can rule out a grounding issue . Where everything grounds on the motor I have a ground running to the batt one to the body and one to the frame so I think that wouldn't be my problem...

Frank
Motor has 5 miles on it since I bought it from blanes motor supply in Dallas as a short block. So i don't think the chain could be streched. Dampener I found out the relation of the key way and the timing mark from a carb modle and a tbi is around 45 degrees different and so are the timing tab is different as well that's why I swapped them out for the correct ones . Firing order is correct and the (dizzy) doesn't seem to be a tooth of at all. Knock sensor? It's new but I'm not sure it can cause this many problems even if it's nonexistent ?
Thanks for everyone's input so far
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RIG: what's left of a 88 yota 4runner lsLQ4 turbo 350 with Kevlar clutches and reverse manual valve body, 203/205 doubler duel steering rocks on 49"Iroks h1's,18" radflo's ,Psc steering, dual wilwood master cly and a harbor freight 12k winch

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Old 07-18-2011, 09:53 AM   #7 (permalink)
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Are you using the incorrect timing tab? Also why did you buy a brand new engine that is wrong. In my opinion, you should have bought a tbi long block with correct head, cam and intake to match the computer. Bet that motor looses a rod bearing within 10k
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Old 07-18-2011, 10:02 AM   #8 (permalink)
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Are you using the incorrect timing tab? Also why did you buy a brand new engine that is wrong. In my opinion, you should have bought a tbi long block with correct head, cam and intake to match the computer. Bet that motor looses a rod bearing within 10k
Why? I swap TBIs onto older long blocks all the time. Doing another one right now. It will need a little tuning, but its stupid simple.



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Old 07-18-2011, 10:16 AM   #9 (permalink)
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Why? I swap TBIs onto older long blocks all the time. Doing another one right now. It will need a little tuning, but its stupid simple.
"Tuning" is the key word. You think OP has all that under control You cant just throw tbi on any cam and expect it to be ok without comp changes.
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Old 07-18-2011, 10:22 AM   #10 (permalink)
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"Tuning" is the key word. You think OP has all that under control You cant just throw tbi on any cam and expect it to be ok without comp changes.
Pay someone to do it?
Personally I'd take an old 4 bolt main with a decent intake over a tbi longblock any day.......I've put TBIs on .030 over blocks with an RV cam and had to do nothing to them, not even bump the fuel pressure. The issues hes having sound more like fucked up wiring or a bad sensor.

Disconnect the knock sensor and spark retard module and see if it gets any better.
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Old 07-18-2011, 10:38 AM   #11 (permalink)
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Pay someone to do it?
Personally I'd take an old 4 bolt main with a decent intake over a tbi longblock any day.......I've put TBIs on .030 over blocks with an RV cam and had to do nothing to them, not even bump the fuel pressure. The issues hes having sound more like fucked up wiring or a bad sensor.

Disconnect the knock sensor and spark retard module and see if it gets any better.
Agreed thats not his existing problem, just curious on engine decision. I am gonna guess there is nothing special about the engine he listed. As for tbi, they are not all that ok with performance parts in stock form, but not my engine
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Old 07-18-2011, 03:12 PM   #12 (permalink)
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Bought the motor because originally it was carburated and since we all know they don't work on the rocks. It was time for a upgrade.... so this was is the cheapest and easiest way to keep her from dieing on off camber stuff. Trust me if I had the coin it would have a ls motor in it hoss
Spdir wiring harness is brand new ALL SENSORS ARE NEW AS OF LAST THURSDAY

As far as first action I'm going to buy a fuel pressure gauge so I know for sure that's not a contributing factor. Then I will unplug the 2 sensors mentioned and give it a whirl ...
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Old 07-19-2011, 04:48 AM   #13 (permalink)
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Are you sure the distributor isn't installed 180 degrees off? Pull the drivers side valve cover, remove plugs, watch the intake valve go up and then down, and the rotate the harmonic balancer to zero. That will be tdc on the intake stroke of a 720 degree cycle. Pull the distributor cap and see if it aligns with the number 1 plug wire.
I've made the mistake of thinking tdc is when dots on the timing chain align it's at tdc. However, it is when the dot on the cam gear is on top that it's tdc of the intake stroke.
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Old 07-19-2011, 09:34 PM   #14 (permalink)
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Fuel pressure gauge is installed with a stock tbi filter. Random loss of power fixed. However idle surge is still there with everything plugged in. I have the timing set to 8 degrees advanced idle was at 580 or so. Resetting the computer and plugged everything in we will see momentarily what it does also replaced the last sensor I could, "the electronic spark control" . Sucker was 80 bucks hope it helps
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RIG: what's left of a 88 yota 4runner lsLQ4 turbo 350 with Kevlar clutches and reverse manual valve body, 203/205 doubler duel steering rocks on 49"Iroks h1's,18" radflo's ,Psc steering, dual wilwood master cly and a harbor freight 12k winch

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Old 07-19-2011, 11:18 PM   #15 (permalink)
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Seems to be doing better first few cranks it would die almost right away and then with every try it would idle longer and longer. Guess it's a slow learner......


Next question? If the idle screw has been tampered with how or what's the best way to get it as close to the factory setting? And are there any advantages of opening it up a lil more than stock?
And Is there any objection to setting these motors with a vacume gauge?
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RIG: what's left of a 88 yota 4runner lsLQ4 turbo 350 with Kevlar clutches and reverse manual valve body, 203/205 doubler duel steering rocks on 49"Iroks h1's,18" radflo's ,Psc steering, dual wilwood master cly and a harbor freight 12k winch

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Old 07-20-2011, 04:34 PM   #16 (permalink)
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First a motor will not run 180 degrees out... sorry...

you changed harmonic balancers.. did you change the tab as well.. when a motor is at TDC it doesnt matter what balancer you use.. TDC is TDC.. its a matter of geometry....

my opinion.. put the old balancer back on and set it to 0 degrees of advance.

if you need to find the compression stroke. put a finger over the number one plug and turn the motor over.. it will push your finger off only on the compression stroke.
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