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  1. #1

    Default any mechanics???HELP!!!

    Hi Guys, I have a 1987 firebird with a 305, 5 speed manual. At certain times it will back fire badly and I can't even barely touch the gas w/o it dying. I just limped it home at 30 mph in 4th gear while just barely touching the gas pedal. One mechanic told me that the distributor was getting too hot and the springs were expanding too far and it couldn't keep it's timing. Another said it was vapor locking. It's carbureted and I don't know what the heck is going on. HELP!!

  2. #2
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    Is that a 3/4 ton or 1 ton Firebird truck?

    It does sound like it could be a distributor/timing issue but the "hot spring story" that you got from the mech sounds like kind of a "stretch".. It could also be a valve hanging open, vacuum leaks, the list is long.
    Can you give a little history on this engine, Modifications? what repairs you've done? tuneups recently? etc. I had an "85 IROC with TPI, same block, etc What does this one have for induction. Does this engine see a lot of high rpms??
    Last edited by stephan; 10-10-2010 at 10:14 PM. Reason: correcting errors, & more ques.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  3. #3

    Default

    I bought the car from my boss and I had to replace the water pump and a few vacuum lines. There are still a few vacuum lines that could be replaced. This has happened twice now with a 2 month interval. It backfired and acted the same way 2 months ago but then it sraightened out until now. I haven't tuned it yet, it's completely stock and I do give it high rpm's but not real often.
    Last edited by hskerprid; 10-10-2010 at 10:09 PM.

  4. #4
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    IF it's completely stock then it doesn't have a carb it has a TBI system. What can you tell me about the ignition timing. Have you got the lightest springs you can get for it? What kind of mech experience do you have? Can you check the timing and tell me the initial, the mechanical, and the total advance? Are you sure it is a carb. and not throttle body injection? Some of these cars were swapped out early on with carbs and distributors, but you said it's completely stock so it would be TBI (they look like carbs from the outside but are totally different everywhere else). Since you are not the original owner you need to be sure exactly what you have on there, or I won't know what we're dealing with. Maybe you could call the previous owner and ask?
    Did this problem start shortly after you had the vacuum hose issues?

    edit***
    when this backfires is it blowing back through the intake or out the exhaust?
    Last edited by stephan; 10-11-2010 at 03:57 AM.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  5. #5

    Default

    Lets rule out vapor lock first thing, as noted if it's stock induction it's TBI which uses an in tank pump that pushes the fuel, this rules out vapor lock because vapor lock is fuel turning into a vapor as it's being drawn to the carburator. When an engine vapor locks it has no fuel in the combustion chamber to burn and dies of fuel starvation.
    I'm betting either a stickey valve (which is actually common on the 305 when it gets high mileage) or a malfunctioning ignition (again high mileage issue) the ignition should be electronic and shouldnt have any springs in it.
    I'd probably change the distributer out. Look at the ignition grounds, make sure everything is properly grounded and the cap doesnt have any cracks.

  6. #6

    Default

    Quote Originally Posted by stephan View Post
    IF it's completely stock then it doesn't have a carb it has a TBI system. What can you tell me about the ignition timing. Have you got the lightest springs you can get for it? What kind of mech experience do you have? Can you check the timing and tell me the initial, the mechanical, and the total advance? Are you sure it is a carb. and not throttle body injection? Some of these cars were swapped out early on with carbs and distributors, but you said it's completely stock so it would be TBI (they look like carbs from the outside but are totally different everywhere else). Since you are not the original owner you need to be sure exactly what you have on there, or I won't know what we're dealing with. Maybe you could call the previous owner and ask?
    Did this problem start shortly after you had the vacuum hose issues?

    edit***
    when this backfires is it blowing back through the intake or out the exhaust?
    It is carbureted not a TBI. I know the difference because I had issues with the TBI on my truck. It backfires through the exhaust ( enough to blow apart the muffler) and a little through the Carb. I drove it to work today with no problems, but I didn't give it a chance to get hot by sitting in alot of traffic. I also noticed that it has a mechanical fuel pump but when I turn the key at initial start I hear a "clattering" sound near the gas tank that sounds like an electrical pump.
    When the problem occurs I can hardly put any pressure on the gas pedal. Since the last 13 miles of my commute is a straight country road ( which by the way is where the problem always begins at)I don't put any pressure on the gas. I go through the gears at just idle speed and let it eventually gain speed to get it home. If I do attempt to press on the gas pedal it stalls and back fires like heck. Sounds louder than a 12 gauge.

  7. #7
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    But this never happens when it's cold? Only when it's hot? I don't know where you live so don't know what the climate is. *I'm assuming you are saying when the engine is hot, but engine should be hot after you have driven 3 or 4 miles if you have a properly working thermostat in it.
    *How many miles do you drive when this problem starts happening?
    *Are you talking about the engine being hot or the ambient air temperature being hot?
    *Do you have a timing light you can put on it and see what the timing is doing? I fixed a Nova recently that was acting similar, & it was the timing chain & sprockets worn out. The plastic on the cam sprocket was trashed and allowed it to jump a tooth and screwed the valve timing AND of course the ignition timing too? But if it is this, it should do it when it is cold too..
    *How many miles are on this car?
    *Has it got the (original) stock distributor or was it replaced when the TBI was?

    Also, you need to stop any high rpms untill we figure out what this is. If it's a cam chain/sprockets gone bad, you could destroy the valves/heads/pistons, & more..

    The noise you hear in the rear is a pump, no worries.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  8. #8

    Default

    Quote Originally Posted by stephan View Post
    But this never happens when it's cold? Only when it's hot? I don't know where you live so don't know what the climate is. *I'm assuming you are saying when the engine is hot, but engine should be hot after you have driven 3 or 4 miles if you have a properly working thermostat in it.
    *How many miles do you drive when this problem starts happening?
    *Are you talking about the engine being hot or the ambient air temperature being hot?
    *Do you have a timing light you can put on it and see what the timing is doing? I fixed a Nova recently that was acting similar, & it was the timing chain & sprockets worn out. The plastic on the cam sprocket was trashed and allowed it to jump a tooth and screwed the valve timing AND of course the ignition timing too? But if it is this, it should do it when it is cold too..
    *How many miles are on this car?
    *Has it got the (original) stock distributor or was it replaced when the TBI was?

    Also, you need to stop any high rpms untill we figure out what this is. If it's a cam chain/sprockets gone bad, you could destroy the valves/heads/pistons, & more..

    The noise you hear in the rear is a pump, no worries.
    I live in NE Kansas it was about 65 today. Last night when I picked up my son it was about 55 degrees. It ran fine on the 18 mile drive there. But about 7 miles in on the way home it began the problem again. I got it home and she sat over night and cooled. I crossed my fingers this morning on my way to work and everything is fine. No problems on the way home either.
    I have noticed when the engine heats ( I just put a 195 thermostat in it) up to operating temp and then she goes up to 210 sometimes between the thermostat opening and closing. The other day it was warmer and I could tell the engine compartment was real hot. That 305 takes up all the room in there and everything is cramped. It also happens more often when I stop at the store after work for groceries and then head for home. As I recollect now, last night I stopped at Mickey D's for my son. I turned it off while he went in and it started the problem 2 miles from there. It has 210,000 on it. I'am about 80% sure that it is the original distributor also.
    Last edited by hskerprid; 10-11-2010 at 07:38 PM.

  9. #9

    Default

    The reason that it isn't tbi is because it most likely wasn't a V-8 either.I have seen a bunch of camaros,firebirds,and ta's that had smaller motors in them and most of them now have a carbed V-8.Check the vin to find out what motor the car came with for sure because if it's not the original motor then you don't know what has been done to it or what it came out of.And if it even has a slightly bigger than stock cam the timing light idea won't work because it won't give an acurate reading.


    03 Chevy Silverado 1500 ext cab Z-71
    79 AMC Spirit GT
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  10. #10

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    Quote Originally Posted by Z-71 View Post
    The reason that it isn't tbi is because it most likely wasn't a V-8 either.I have seen a bunch of camaros,firebirds,and ta's that had smaller motors in them and most of them now have a carbed V-8.Check the vin to find out what motor the car came with for sure because if it's not the original motor then you don't know what has been done to it or what it came out of.And if it even has a slightly bigger than stock cam the timing light idea won't work because it won't give an acurate reading.
    I just checked the VIN. It is the original 305 carbureted engine.

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