NEED HELP 2003 TB 4.2. Wont go over 5mph

Joshj517

Original poster
Member
Feb 18, 2019
3
Alabama
Hello everyone. So far I have changed all coil packs. Spark plugs. Throttle body. And accelerator pedal. And it still won't go over 5mph. It's at the mechanic shop and they don't know. They unplugged the o2 sensor and said there was no change. But about a year ago when I passed a vehicle it smelled like rotten eggs. And it also threw a code for a camshaft sensor. But the mechanic said it couldn't be that because my vehicle doesn't run hot? Please help
 

Redbeard

Member
Jan 26, 2013
3,466
What codes are you showing? It's hard to diagnosis without any codes. What is the history of this vehicle? Has the fuel filter been changed recently?
 

Sparky

Member
Dec 4, 2011
12,927
Don't just unplug the O2 sensor. Unscrew it completely.
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Was the Reduced Engine Power light up?
 

Chickenhawk

Member
Dec 6, 2011
779
Stop throwing parts at it that have nothing to do with your problem unless they are throwing their own codes. When a vehicle cannot go over 5 mph and there are no codes, there are only two very common causes: transmission issues and a plugged cat converter. Get a new mechanic and get your cat PROPERLY checked with a backpressure test, not just a "well, it can't be the cat because it's not overheating." The reason it is not overheating is simple ... it's not flowing any exhaust. Temperature checks and IR thermo checks help identify PARTIALLY plugged cats, but they are most useful with inefficient cats. Yours is plugged completely.

Replace the cat and find out how it became plugged, or you will be doing it again in six months. Did you ever drive it with a flashing check engine light? What is the position of the needle on your coolant temperature gauge? Answers to these questions are important.

If your backpressure test is fine (0 PSI at idle, and no more than 1 PSI at 2500 RPM) then look at the transmission. When parts fail in the transmission, they can mimic fuel, intake or exhaust problems. But always go with the cheapest and easiest to diagnose first. This is why my money's on your cat needs replacing.
 

Joshj517

Original poster
Member
Feb 18, 2019
3
Alabama
Yes when I started driving the check engine wind flash. My temp never gets hot unless it's really hot outside and it's just idling. Other than that around 180-210

Stop throwing parts at it that have nothing to do with your problem unless they are throwing their own codes. When a vehicle cannot go over 5 mph and there are no codes, there are only two very common causes: transmission issues and a plugged cat converter. Get a new mechanic and get your cat PROPERLY checked with a backpressure test, not just a "well, it can't be the cat because it's not overheating." The reason it is not overheating is simple ... it's not flowing any exhaust. Temperature checks and IR thermo checks help identify PARTIALLY plugged cats, but they are most useful with inefficient cats. Yours is plugged completely.

Replace the cat and find out how it became plugged, or you will be doing it again in six months. Did you ever drive it with a flashing check engine light? What is the position of the needle on your coolant temperature gauge? Answers to these questions are important.

If your backpressure test is fine (0 PSI at idle, and no more than 1 PSI at 2500 RPM) then look at the transmission. When parts fail in the transmission, they can mimic fuel, intake or exhaust problems. But always go with the cheapest and easiest to diagnose first. This is why my money's on your cat needs replacing.
I was doing what the mechanic said was the problem
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
Your temp gauge should never be anything other than almost 12oclock 210 degrees, CONSISTENTLY, except on cold engine start up.

If its reading below that, than you have already found 1 of your problems, thermostat.

Also, there is an easy way to tell if you have a plugged CAT, remove the O2 sensor, and try driving it. If you go over 5 MPH, than you may have found your problem.
 

Chickenhawk

Member
Dec 6, 2011
779
It's a chain. Misfires cause raw fuel in the cat. (This is why the check engine flashes, and the owners manual says to pull over immediately.) Low coolant temps cause rich mixtures in the long term, which plugs cats. Step one is find and fix the cause of the misfires. (Hopefully you have done that.) Step two is to replace the thermostat and the coolant temp sensor. Step three is to check the cat and replace it. (Trust me; it's toast.) All will be well.

Someone in there, you might want a new mechanic.
 

gmcman

Member
Dec 12, 2011
4,656
Post the codes please.

Just to throw this out, don't think it's your issue...but I had my TB harness cut years ago, would only go 5-10 MPH. Make sure none of the pins are pulled away from the plastic connector. Does the throttle body open fully?
 

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