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Car Forum / GMC Cars / January 20061983 LeSabre 5.0 engine sputtering under load
HI all, I'm trying to help my dad figure out what is wrong with his 83 lesabre with 5.0L (307) engine and quadrajet carb. It starts and runs fine in neutral and park. It'll idle fine in gear but when you try to accelerate it starts sputtering. When the engine is cold, it's hard to get 'er above 35 MPH. We checked the timing because it felt like a timing issue, and the ignition timing is fine. It got a new timing chain and gears last fall and had been running fine since then until now. The exhaust does not smell of fuel so I assume it's not an excess of fuel. The fuel filter was replaced already today. Any ideas? We did notice during out 'array' of tests that the choke plate on the two back carb barrels never open (well, unless you open them by hand). Thanks for any help you can offer. You will never see the secondary plates open until open full throttle and the choke would have to be off, these are not choke plates. Did you replace the small fuel filter in the carb inlet? Many things can cause this, if you are not fully familiar with checking the coolant temp sensor and the operation of the carb mixture solenoid and tps you may need professional help with this. > HI all, I'm trying to help my dad figure out what is wrong with his 83 > lesabre with 5.0L (307) engine and quadrajet carb. [quoted text clipped - 14 lines] > > Thanks for any help you can offer. Thank you for the help. I think I'll suggest he buy a repair manual for his car (I always buy one for my vehicles). I can't believe the carb has a tps! Would it be used for timing advance only? Hopefully the test procedure for the tps would be in there. I'm starting to wonder if the fuel pump is going out.... and the carb looks like it could use a good cleaning. If the tps only controls timing advance then I'm inclined to rule that out. I have driven carbeurated vehicles without operational timing advance and this doesn't feel like that sort of issue. I also wonder about the carb mixture solenoid. If the solenoid were stuck closed I'd have the opposite problem, wouldn't I? If it were stuck too far open then I'd probably smell gas. I think I'll suggest he picks up a loaner fuel pressure gauge too.... I'm starting to wonder about the fuel pump. He told me he changed the fuel filter; I'm not sure which filter! Thanks for getting me closer to a solution. 8^D > You will never see the secondary plates open until open full throttle and > the choke would have to be off, these are not choke plates. Did you [quoted text clipped - 27 lines] > ----= East and West-Coast Server Farms - Total Privacy via Encryption > =---- > I'm starting to wonder if the fuel pump is going out.... and the carb looks > like it could use a good cleaning. I don't know if I'd jump to this one yet (fuel pump). If I understand what you say correctly, the car won't even gently rev up enough to drive it above 35mph or so - correct? In other words, if you are sitting in park and are just trying to rev it to 3K or so a few times in a row, what happens? Does it rev right up or does it hesitate? Some things to look for when you're doing this - take the air cleaner off and watch and listen - do you get a good spray of fuel when you pump the carb? Can't really describe well what you want to see/hear but the best I can do is to say you should hear the spray when you pump the carb. Do it a bunch of times in rapid (sort) succession. Does it rev up nicely every time? There's a filter screen in the fuel line input to the carb that gets clogged. It's worth looking at. When it gets clogged you can experience starvation problems that will sometimes make themselves apparent by the above procedure. Sometimes not. It's so easy to check though that it's worth simply pulling the line. > If the tps only controls timing advance then I'm inclined to rule that out. > I have driven carbeurated vehicles without operational timing advance and > this doesn't feel like that sort of issue. I also wonder about the carb > mixture solenoid. If the solenoid were stuck closed I'd have the opposite > problem, wouldn't I? If it were stuck too far open then I'd probably smell > gas. Man... this is taxing. I'm trying to remember back to my Delta 88 with the same motor. It almost hurts to try to remember back that far! An old memory is a terrible thing. I think I'd still go back to the question of how the carb performs in the garage with gentle input - does it take the engine up to 3K?  Signature-Mike- mmarlowREMOVE@alltel.net >> I'm starting to wonder if the fuel pump is going out.... and the carb > looks [quoted text clipped - 8 lines] > Does > it rev right up or does it hesitate? If you rev it in park it starts to sputter at (I guess) around 3k rpm. It only won't go above 35 when the engine is cold. I have not driven the vehicle; just looked at it in my driveway. I assume it does eventually get up to cruising speed when the engine warms up since he specified 'when the engine is cold'. > Some things to look for when you're doing this - take the air cleaner off > and watch and listen - do you get a good spray of fuel when you pump the [quoted text clipped - 3 lines] > bunch of times in rapid (sort) succession. Does it rev up nicely every > time? If you gently rev it to anything under what sounds like 3k rpm it does great. I have manually operated the fuel accellerator pump with the engine off and it does spray every time. When we were testing the back 2 bbls of the carb he revved 'er good... it definately went to above 3k rpm. But you could tell it wasn't firing right. > There's a filter screen in the fuel line input to the carb that gets > clogged. It's worth looking at. When it gets clogged you can experience > starvation problems that will sometimes make themselves apparent by the > above procedure. Sometimes not. It's so easy to check though that it's > worth simply pulling the line. I'm going to have to ask him which filter he changed. If there's more than one I doubt he changed them all. >> If the tps only controls timing advance then I'm inclined to rule that > out. [quoted text clipped - 11 lines] > how the carb performs in the garage with gentle input - does it take the > engine up to 3K? It's a little hard to describe. It will (while running very rough and sputteringly) rev to above 3k rpm, but it's not pretty. It lacks power when in drive. I gently power braked it (of course without spinning the tires) and it runs great until you get to a certain rpm, then it starts sputtering and losing power. That's when he told me it won't even go above 35 mph when it's cold. He hasn't even been back since he brought it over for me to check out. It'll be nice to have these suggestions when he comes back. I told him I was going to ask around on the web. Thank you very much for your help and time. > It's a little hard to describe. It will (while running very rough and > sputteringly) rev to above 3k rpm, but it's not pretty. It lacks power when [quoted text clipped - 8 lines] > > Thank you very much for your help and time. Hey - a thought just occurred to me. Have you covered all of the basic tune up checks yet? Signature-Mike- mmarlowREMOVE@alltel.net |
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