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Old 09-08-2010, 07:07 PM
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1990 tbi 350 no power

I recently rebuilt the 350 in my moms 1990 Chevy 1/2 ton 2wd pickup. It has less power than before I rebuilt it. Its not to bad when you are just off idle driving around, but when you give it about half throttle it doesn't pull at all. It's not throwing any ecm codes. it idles a little rough when cold but not too bad when warm, the following parts are new:

dist cap/rotor/wires/plugs
air filter
fuel filter
distributor
throttle body gaskets/ o rings

Its got about 13 inches of vacuum at idle
13 psi fuel pressure at idle
timing was set at 0 tdc w/wire on fire wall disconnected

I've read that you can check the fuel injector patterns with a timing light and they should be cone shaped, mine just kinda dribble. Mitchell on demand says that a pattern test won't work on these tbi's, but not sure about that.

Anyone have any suggestions?

Mike

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Old 09-08-2010, 07:18 PM
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Sounds like you dont have the base timing set correctley. When you set the timing did you have the timing connector unplugged ? Wire is underhood at the relay center in front of passenger on the firewall.The wire color is tan / w black stripe it sticks out of the harness and it has a connector you unplug. It may also be inside (possibly) in front of the passenger up at the top edge of the carpet or just behind it below heater box. setting should be 0 degrees.
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Old 09-08-2010, 07:19 PM
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Also dont worry to much about the sprayers as they are naturally dribbly. as long as there pretty much cone shaped , youre good.
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Old 09-08-2010, 07:42 PM
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I did the timing with the connector unplugged and have rechecked it about 3 or 4 times, the injector pattern is cone shaped on one side, but I'm not seeing much fuel out of the other. Shouldn't it be a real fine spray?

Thank you for the response,

Mike
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Old 09-08-2010, 08:20 PM
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no . It wont be real fine. It will probably look like a small garden hose on fan setting.BUT both sides should look alike. Good thing there is 2 as you have something to compare too.
Also balancers have been known for the outer ring to slip. Did you ever check to see if tdc number one piston was where the mark indicated at the timing indicator.
From the sounds of the injector spray ( one being less than the other) I would start there.
Take a good look at them. Put a light behind them and that way you can see them better.They are naturally dribbly.as long as they both look the same and they spray a cone shape you are good to go.
Do you have any trouble codes?
What are the fuel trims doing. Got any Oxygen sensor activity?
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Old 09-09-2010, 01:06 PM
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I rechecked the injector pattern with the timing light behind the injectors, and it helped alot. They are both cone shaped, one may be spraying slightly less fuel, but it might be a trick of the light. I will check to see if the outer ring has slipped on the balancer. I dont have any trouble codes, I have been checking them with a jumper between a and b terminals on the connector under the dash, as I don't have a scan tool. What are the fuel trims? I dont have a scanner to check o2 sensor activity. I did set the timing with the connector unplugged.

Mike
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Old 09-09-2010, 01:41 PM
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Set your base timing to around 6 instead of 0. It will pick it up quite a bit over stock and shouldn't have any problems with detonating. 87 octane will still be ok.
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Old 09-09-2010, 01:51 PM
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Quote:
Originally Posted by yeepman2
I recently rebuilt the 350 in my moms 1990 Chevy 1/2 ton 2wd pickup. It has less power than before I rebuilt it. Its not to bad when you are just off idle driving around, but when you give it about half throttle it doesn't pull at all. It's not throwing any ecm codes. it idles a little rough when cold but not too bad when warm, the following parts are new:

dist cap/rotor/wires/plugs
air filter
fuel filter
distributor
throttle body gaskets/ o rings

Its got about 13 inches of vacuum at idle
13 psi fuel pressure at idle
timing was set at 0 tdc w/wire on fire wall disconnected

I've read that you can check the fuel injector patterns with a timing light and they should be cone shaped, mine just kinda dribble. Mitchell on demand says that a pattern test won't work on these tbi's, but not sure about that.

Anyone have any suggestions?

Mike
Manifold vacuum is way too low, sounds like an air leak into intake system somewhere.

Bogie
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Old 09-09-2010, 02:26 PM
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ok, I'm beginning to think my base timing maybe off. I rolled the engine over to tdc on number 1, I used a bent piece of brazing wire to feel the piston coming up, as I can't see the piston coming up with the exhaust manifold in the way. Is there a better way to do this? Anyway with the piston at tdc as best as I can tell the timing mark is quite a ways from 0 as shown in the picture. I used one of the double roller timing sets from summit with three keyways, but I thought I used the 0 keyway to keep the timing factory. The balancer looked ok when I installed it and I used the proper puller when I removed it so I don't think I damaged it.

Mike
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Old 09-12-2010, 12:40 AM
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no power

Intake manifold is sucking air and you can bet your EKG valve ports are clogged with carbon. I just went threw the same problem on a 5.7 Chevy suburban. It cost me $146.00 for diagnoses from the dealership but they were right on time. Of course I sure as hell didn't get the dealership to do the work because they wanted $1300.00 for repairs. I had a friend help me install the gasket for $150 bucks.

Tommy
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Old 09-12-2010, 11:25 AM
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EKG valve
???

Right in there with the knuter valve??

I believe you mean the EGR valve.
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Old 09-12-2010, 12:16 PM
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the balancer slipped. replace it then re time the engine
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Old 09-12-2010, 08:16 PM
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I stand corrected

Hit the wrong key "Homeboy" EGR valve, I new I should of looked it up. Anyways ya'all have supplied me with BOO-KOO info in the past and my appreciate goes out to ya'all. Next time I make an attempt to pass something on I will be more careful on what I put in print. I sure don't want to confuse a person anymore than he already is.

Tommy
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