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Help! I can't accelerate!

G

gt1009

1/2 ton status
Joined
Apr 29, 2007
Posts
103
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Location
Wilmington, NC
Hi everyone,
Been away from the forums for a while (full time college student working 40 hours a week). I've been having issues with the truck lately that are really troubling me. When I hit the gas off of a stop the truck will barely move. It takes around 20 seconds for me to top 25 mph. If I hit the gas too hard it will backfire, and today it stalled out on me in an intersection. I really need to get this issue figured out. It seems like about 25% throttle is the best point for it right now, as if I go over that it bogs down. Once I top 30 mph it seems to run a little better, but I still have to floor it to go from 45 to 50. Does anyone have an idea what it could be?

Info on the truck:
90 GMC Jimmy. 298,000 miles
350 TBI, 700R4 transmission.
Recently replaced: Spark plugs, wires, distributor cap and rotor, air filter.
Ran gumout fuel injector treatment through 2 tanks (diluted to about 5 gallons each)
Truck doesn't accelerate anywhere near normal speeds.
 
i would start with a new fuel filter,is it throwing any codes (check engine light)
 
Fuel filter was replaced less than a year ago, so I don't think it's the culprit. Check engine light comes on every once in a while but cuts off when I start it the next time.

Unfortunately the city I live in gives me a pretty horrible driving style. I've owned the truck for two years and have only put about 4k on it, despite a 15 minute commute each way to work/class. I spend most of my time sitting at stoplights or going through stop and go traffic in 25 mph speed zones. Basically as bad for a vehicle as you can get here.
 
Codes should be stored for (I think) 50 starts.
Just because you replaced the filter doesn't mean it's not clogged again if you have crud in your tank. Also, how's your fuel pump doing? Do you hear it making lots of noise?
 
Have you checked your timing? Check your firing order / plug wires on the distributor cap. Could easily be out of time, and with a spark plug wire or 2 crossed
 
I would check your ignition coil. If it looks like it has hard water stains
(white residue) then its been arcing out which will cause a random misfire. What about the 02 sensor. Both these parts should be inspected or replaced during a tune up.
 
Probably the most important question right now,

Did this start right after the Spark plugs, wires, distributor cap and rotor, air filter? Or did you do these things to try to resolve the issue?
 
The basics are fuel, ignition and compression - all at the correct time and in the correct amount.

Get a timing light, follow the directions, and check your timing. Maybe your distributor cap came loose and now is way off.

Remove the fuel line, get a measuring cup (glass) and see how much fuel flows when you turn the engine over.

Check to be sure you have the spark plug wires in the correct firing order. Be sure #1 is in the correct location on the distributor cap.

Check the spark - pull a plug and turn the engine over. Is is nice and bright?

Check the plugs color - are they clean and dry?

Do you smell gasoline at the exhaust? Maybe you have a leaking injector o-ring and are running too rich. Do you see fuel leaking into the intake when the engine is NOT running but the ignition key IS turned on?
 
If it has a catalitic converter still,it may be plugged up,perhaps an exhaust pipe got squashed or a double walled y-pipe collapsed inside.....fuel pressure might be too low....one truck a friend bought after it sat awhile in someone's yard refused to accelerate good until we decided to look at the air filter--the box it resides in was FULL of shells,dead mice and insulation from the carpeting they built a nest from...once we cleaned all that junk out it gained about 100 hp!...
 
y5mgisi said:
Probably the most important question right now,

Did this start right after the Spark plugs, wires, distributor cap and rotor, air filter? Or did you do these things to try to resolve the issue?
Click to expand...
Definitely :waytogo:


Two other things to check.

Check the spray on the TBI to see if that's plugged. Should be a nice even flow.

When was the last time the timing chain was changed? Check for slop. Remove dist cap, pull your plugs, and rotate the engine back and forth to see if the distributor pauses a great deal before it starts to move.
 
It helps a lot when I changed my fuel filter. I do it about every two years. You could have gotten a tank of really bad fuel and it clogged up the filter or injectirs.
 
Thanks guys,
This didn't start after little tune up I did. That was done to correct the issue. Ill change the fuel filter and check flow rates as soon as I get a chance. I can't give up on the truck this close to 300,000 miles!
 
Kain said:
^^ if the cats are bad it will smell like rotten eggs
Click to expand...

Not necessarily. Ever been behind a Toyota and smelled it? They smell like rotten eggs when they are new.

The catalyst can come apart and clog itself with no indication.
 
My money is on a fuel pump. They are 45$ on amazon for a AC DELCO one, drop the tank and swap it out in 2 hours total. I had the same symptoms when mine was headed out, a week later all my truck could do was idle, then it would die.
Be sure to clean the tank out when you are in there, usually some rust or particles is what kills the pump.
 
Yeah, I cannot agree more. If you have time, money, and effort to waste then by all means start replacing all the parts. You should replace the tires, brakes, and muffler while you are at it.

If you want to fix the actual problem then you should do some testing first and fix only the actual problem. In fact, if you replace other items you may mask or worsen the real problem.
 
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