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Loren Champlain Sr
Veteran
/ Moderator
Apr 17, 2014, 4:32 PM
Post #26 of 35
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Re: 350 tbi misfire
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acer; Glancing thru the posts, I noticed the listing for the % of cylinder contribution. #1 & #2 cylinders were considerably lower than the rest. I can't picture in my mind any chance of a vacuum leak on those two. Tight valves could definitely be causing the problem. As Tom suggested, a vacuum reading at idle (watching for needle fluctuation) might help. You should be seeing around 17-20hg vacuum at idle. Being an '89, there is probably a shunt that needs to be disconnected to check timing. If memory serves, valve adjust is zero lash, plus 360 degrees at operating temp. I usually set them at zero plus 1/2 turn, as I'd rather be a bit loose than too tight. Just thought of something else to check. #1 & #2 are next to each other in the firing order. Check the distributor cap for a carbon track between the two. Long shot, but worth a look.
Loren
SW Washington
(This post was edited by Loren Champlain Sr on Apr 17, 2014, 4:42 PM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 17, 2014, 5:53 PM
Post #27 of 35
(2929 views)
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Re: 350 tbi misfire
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Something else you might want to try on this is a "running compression test". These things are pretty notorious for wearing off camshaft lobes.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Apr 17, 2014, 6:05 PM
Post #28 of 35
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Re: 350 tbi misfire
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Nice to see you Loren however far away always think of you.
This engine has a new non OE cam and parts or bits or broken crap found. Yes some OE cams suked or lasted forever. Bet it gets no lube and valves don't know what the heck to do nor lifter pressure up. Compression or vacuum is informative but vacuum test could be real telling and easier or quicker anyway.
Good nautical chain got expensive lately (to make it a mooring) but can smell this engine is violated and a shame as they are durable engines,
T
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acerulz
User
Apr 17, 2014, 7:45 PM
Post #29 of 35
(2919 views)
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Re: 350 tbi misfire
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well I dug deeper tonight and found that only #3 intake and #5 exhaust were loose and popped the retaining clips. Don't know if it's been like this since it was built and adjusted but still doesn't account for a flutter on the other side of the engine. On the plus side, both clips were sitting on top of the lifter so at least they didn't make friends with the oil pan and/or pickup. There is absolutely no damage to the cam or lifter so another plus. I'm seriously thinking on bolting on vortec heads while I'm in there. I got a good set of 062 heads for cheap. See if that cures the misfire and add some power too at the same time. Would just have to buy the intake and adapter for tbi. Wondering tho, I removed the vortec heads and found white sealant on the bolts. Is this a possible sign that the engine has been rebuilt? It looks in really good shape but the donor truck had 350,000km on it so I'm kind of thinking its been rebuilt recently.
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acerulz
User
Apr 17, 2014, 7:48 PM
Post #30 of 35
(2918 views)
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Re: 350 tbi misfire
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Loren, I checked the cap and there is no carbon tracking going on in there, but good call to check it. I overlooked that one.
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acerulz
User
Apr 17, 2014, 7:53 PM
Post #31 of 35
(2915 views)
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Re: 350 tbi misfire
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a thought just popped into my head here, but could my flutter/misfire be caused by not having a crossover pipe between left and right pipes?
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 18, 2014, 2:27 AM
Post #32 of 35
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Re: 350 tbi misfire
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Another common issue to this engine is the rocker studs pulling out of the head and causing the valves to loosen up.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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acerulz
User
Apr 18, 2014, 10:40 AM
Post #33 of 35
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Re: 350 tbi misfire
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ya I've heard a lot about that, but they all seem to be good.
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acerulz
User
May 3, 2014, 3:49 PM
Post #34 of 35
(2877 views)
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Re: 350 tbi misfire
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just an update, but I changed the heads out and the flutter is gone. vortec heads, performance plus cyclone intake, tbi adapter and throttle body spacer to my 350 tbi. Engine has a mild cam in it, and headers with dual 2 1/2 pipes. Engine runs great around 6 degrees, but can't get rid of a power loss when I slam the gas down. It falls on its face and backfires through the intake. If I don't slam it down and just moderately go to WOT it keeps up but just doesn't seem to have as much power as it should have. I bumped up the regulator to 15 psi also. Wondering if I have to put 454 injectors in it, or if I should get a custom burn prom for it? If I go prom, how can I tell what my cam specs are without a cam wheel? Any good sites for a custom prom? thanks in advance!
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Discretesignals
Ultimate Carjunky
/ Moderator
May 3, 2014, 4:48 PM
Post #35 of 35
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Re: 350 tbi misfire
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I'm personally not a race engine builder, but when you start modifying a speed density engine, or any FI engine really, you get to the point where the software in the PCM has to be modified if you want full potential from your creation. In extreme cases not modifying the software can cause engine damage.
The MAP sensor along with the ECT and TPS are the primary sensors the PCM uses to calculate engine load on a speed density engine. The engine load calculation along with RPM is used by the PCM to determine where in the ignition advance and fuel curves, stored in the PCM's calibration chip, it should be at to inject the correct amount of fuel and provide the correct amount of advance. When you alter the characteristics of the engine itself beyond what the original fuel curve and ignition advance maps were designed for, you'll have to do some remapping or you'll have drive-ability issues.
Of course, if you have other problems such as low fuel pressure, low fuel volume, injectors with not enough flow rate, flaky sensors, and/or an ignition system that cannot keep up with the demand of higher combustion chamber pressures, no amount of tuning is going to solve your problem.
Maybe it would be a good idea to have a talk with an engine tuner.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on May 3, 2014, 4:50 PM)
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