1990 F150 5.0 engine problems
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1990 F150 5.0 engine problems
Hey guys. I'm new to the forums as well as owning a Ford truck. I've got a 1990 F150 XLT Lariat 5.0L Manual 2wd that's giving me some problems. For one, it idles high. I'm sure that's probably a vacuum leak somewhere But, what's got me stumped is this: when under a load at low rpms all it seems to do is stutter like it's running on 4 or 5 cylinders. Extremely under powered. Once you get above about 2500 rpms it smooths out some, but still feels under powered. It has new motorcraft plugs and new wires (I think they're "exact fit"). I've routed the wires so none of them are touching. The truck has dual tanks and it runs the same off either tank. Any ideas? Thanks!
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On a 1991 I am working on I had two cans I just replace with one larger plastic can from a 1994.
Check the two cans on yours and see if the are rusted.
One is on the pass side and the other under the coolant overflow tank.
Good luck.
Check the two cans on yours and see if the are rusted.
One is on the pass side and the other under the coolant overflow tank.
Good luck.
Hey guys. I'm new to the forums as well as owning a Ford truck. I've got a 1990 F150 XLT Lariat 5.0L Manual 2wd that's giving me some problems. For one, it idles high. I'm sure that's probably a vacuum leak somewhere But, what's got me stumped is this: when under a load at low rpms all it seems to do is stutter like it's running on 4 or 5 cylinders. Extremely under powered. Once you get above about 2500 rpms it smooths out some, but still feels under powered. It has new motorcraft plugs and new wires (I think they're "exact fit"). I've routed the wires so none of them are touching. The truck has dual tanks and it runs the same off either tank. Any ideas? Thanks!
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I replaced those today and it is running MUCH better. Still not 100% but I'm happy with the results. Thanks! I think a different set of gears would help out the rest. I'm sure it has the stock gears and the truck has pretty tall BFG All Terrains all the way around (285/70/17). The tires have changed the gear ratio enough to make my speedometer 10 mph off at 55 (says I'm going 55 when actual speed is 65).
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I forgot to mention I cleaned the throttle body and idle air control valve too. Air filter seems fine and I've also replaced the PCV valve.
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Ford Fuel Injection Throttle Position Sensor (TPS) Use this link to test the TPS. Also if you look in the list on the right of that page you will see a link "Self Test" for instructions on getting any stored trouble codes. Might be worth doing.
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Ford Fuel Injection Throttle Position Sensor (TPS) Use this link to test the TPS. Also if you look in the list on the right of that page you will see a link "Self Test" for instructions on getting any stored trouble codes. Might be worth doing.
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The one on the pass side can be check by hooking up just the vac source hose and putting your finger on the other input to the can. Pull your finger off in 30 sec and see if vac holds.
Good to read the truck is getting better.
Good to read the truck is getting better.
I checked the cans--they both seem to be fine. The one under the coolant overflow tank was holding vacuum when I unplugged the hoses. The other one I took off and inspected and it seems sealed tight. The truck still wants to idle around 1200 to 1500 rpms. I checked all the hoses I could see. I sprayed throttle body cleaner around all visible hoses and connections to check for leaks that way and couldn't find anything.
I forgot to mention I cleaned the throttle body and idle air control valve too. Air filter seems fine and I've also replaced the PCV valve.
I forgot to mention I cleaned the throttle body and idle air control valve too. Air filter seems fine and I've also replaced the PCV valve.
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I'll keep posting until I get this thing straightened out. I bought the truck real cheap needing a clutch so I couldn't test drive it. It ran real good sitting in the driveway! ;-) Haha...
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From: So Cal/Mexico
Whatever you do, DO NOT touch the 'idle adjustment' screw at the throttle body. I know it's tempting to do so....but don't.
Btw I bought my Equus OBDI reader at Kragen for $22.00. Much more fun than counting 100's of flashes on the dash......
Btw I bought my Equus OBDI reader at Kragen for $22.00. Much more fun than counting 100's of flashes on the dash......
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Alright, I just now got around to checking the codes... been busy with a cousin's wedding. The code that pulled up was 23 "Closed throttle TPS voltage higher or lower than expected." So, I think we've found the idle problem. I'll replace the tps and check back. Thanks!
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From: So Cal/Mexico
Alright, I just now got around to checking the codes... been busy with a cousin's wedding. The code that pulled up was 23 "Closed throttle TPS voltage higher or lower than expected." So, I think we've found the idle problem. I'll replace the tps and check back. Thanks!
Trust me on this one..........
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I put a meter to it to test the voltage and it was over 2 volts at closed throttle and just under 5 at wide open throttle. I read that it's supposed to be under 1 volt at closed throttle. I disassembled, reassembled and still came up with the same results. So, I think this one is done unless you have any suggestions. I have one waiting on me to pick up in the morning.