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88 chevy 350 w/ tbi problems
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flyinhawaiian6
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Apr 3, 2009, 11:21 AM
Post #1 of 11
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88 chevy 350 w/ tbi problems
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I have a 88 chevy 350 with TBI suburban. It is hard to start and when it starts you have to keep on the gas. If you let off the gas it dies. If you try to put it in gear it dies. I checked the computer and it keeps giving me code 33. I've replaced all the sensors execped the oxygen, and coolant temp sensor. I even temporarily removed the catylitic converter to test if it was a blockage. Tested the fuel pump and filter, nothing wrong there either. Sometimes when I try to start it, it burps a flame out of the throttle boby. I have checked the timing, the heads have been taken off and machined, new gaskets, I can't figure out what is wrong with it. Please help.
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Loren Champlain Sr
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Apr 3, 2009, 3:53 PM
Post #2 of 11
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Re: 88 chevy 350 w/ tbi problems
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Code 33 is for MAP sensor voltage too high. See attachment for diagnostic procedure. The MAP sensor 'reads' manifold vacuum. If it 'sees' a drop in vacuum, it 'thinks' you are under load, and commands more fuel. Soooo, anything that affects engine vacuum, can tell the MAP sensor the wrong information. This can be so many things.
Tight valves, vacuum leak, retarded timing, and the list goes on. But, with the attachment, you can check the MAP itself. Good luck.
Loren
SW Washington
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Attachments:
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Map Sensor.gif
(37.2 KB)
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flyinhawaiian6
Novice
Apr 4, 2009, 12:52 PM
Post #3 of 11
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Re: 88 chevy 350 w/ tbi problems
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The map sensor is brand new. To check it I hooked a vacuum pump to it and checked the voltage with a volt meter. As vacuum went up voltage went down. I'm sorry but the attachment did not help much because step #1 / If engine idle is rough, unstable or incorrect, correct before using chart. Getting it to idle correctly is my problem. I have about 50,000 miles on this rebuild and it is starting to look like I will be doing it again.
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Loren Champlain Sr
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Apr 4, 2009, 4:15 PM
Post #4 of 11
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Re: 88 chevy 350 w/ tbi problems
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>>The map sensor is brand new. To check it I hooked a vacuum pump to it and checked the voltage with a volt meter. <<
That's nice, but what vacuum reading is the MAP sensor seeing? Re-read the original post. I'd hate to see you tear the engine back down for something rather simple, but over-looked.
Loren
SW Washington
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flyinhawaiian6
Novice
Apr 4, 2009, 4:27 PM
Post #5 of 11
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Re: 88 chevy 350 w/ tbi problems
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I can not use the guide you gave me because I can not get the engine to idle. Got any other ideas? I will try to check the vacuum to the map sensor.
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Loren Champlain Sr
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Apr 4, 2009, 4:36 PM
Post #6 of 11
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Re: 88 chevy 350 w/ tbi problems
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1. Recheck valve adjustment. Too tight can cause your problem.
2. Recheck timing. Retarded timing can cause your problem.
3. Recheck for vacuum leaks. Intake manifold, TBI base, EGR closed?, ect.
4. If you rebuilt the motor yourself, may want to recheck timing marks on chain. Could be a tooth off.
Loren
SW Washington
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flyinhawaiian6
Novice
Apr 10, 2009, 1:35 PM
Post #7 of 11
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Re: 88 chevy 350 w/ tbi problems
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I turned the distributor a little to the left (as you are looking at it under the hood). It now stays idling by its self, and does not die when you put it in gear. The idle is rough, and I still get a code 33. I'm also getting a code 45. I'm getting 5 in. of vacuum at the throttle body where the map sensor line plugs in. I plugged the vacuum gauge into the intake manifold and the bounces between 6 and 9 in. of vacuum. My book said it should be between 18 and 22. I'm not sure what all this means. It sure makes me feel like this little guy.
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Loren Champlain Sr
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Apr 10, 2009, 3:18 PM
Post #8 of 11
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Re: 88 chevy 350 w/ tbi problems
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When you turn the distributor clockwise, you are retarding the timing. The low manifold vacuum will cause the MAP sensor to command more fuel, causing an overfueling problem. Read the suggestions in the prior replies. After you've done those checks, let us know the results. Have you actually checked the timing with a timing light?
Loren
SW Washington
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flyinhawaiian6
Novice
Apr 11, 2009, 5:36 PM
Post #9 of 11
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Re: 88 chevy 350 w/ tbi problems
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I turned the engine over so that they were on the compression stroke. I backed them off so that the push rods turned easy between my fingers. I then tighten them down till I could just feel a change in the way they turned. Then I loosened them a 1/4 of a turn. Yes I had them a bit tighter than this to begin with. I hoped this was my fix, but it did not change the idle. In fact a couple of valves are rattling now but at least I now they are not to tight. I checked all the vacuum lines for leaks. I check all around the throttle body for leaks and the intake manifold. I found no leaks. The EGR opens and closes. I pulled the timing cover off and the marks are on. I also did a compression check I can give you those results if you think they will help. I have not put a timing light to it yet, but I will and let you know what the results are. Thanks for all your help so far. 
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Loren Champlain Sr
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Apr 11, 2009, 8:16 PM
Post #10 of 11
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Re: 88 chevy 350 w/ tbi problems
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flyinhawaiin; With the engine running, valve cover off, loosen one rocker arm at a time until it clatters. Tighten it until the clatter just stops. Then, in 1/4 turns at a time, tighten the rocker arm one full turn. Each time you turn it 1/4 turn, the engine will stumble. Let it recover before going another 1/4 turn, and so on. This makes a hell of an oily mess, and a lot of smoke from the oil hitting the exhaust manifold. You can buy a set of 'clips' that attach to the rocker arms that will deflect the oil back to the head so it doesn't hit the exhaust.
If you've got the compression readings, go ahead and post them. The more info, the better.
Loren
SW Washington
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flyinhawaiian6
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Apr 13, 2009, 5:11 PM
Post #11 of 11
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Re: 88 chevy 350 w/ tbi problems
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Here is the results of my compression check #1= 150, #3=152, #5= 148, #7= 149, #2=149, #4=149, #6= 151, #8= 128. I took another check 5 min. later here are those results. #1= 151, #3= 127, #5= 148, #7=126, #2= 124, #4= 126, #6=151, #8= 149.
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