I have 99 expo 4.6 with engine trouble. Will only run correctly with maf half covered. Idle surges other wise. I suspect a vacuum leak checked all vacuum lines and changed all intake gaskets. I change maf, tps, iac, chts, cam sensor, crank sensor. Now i dont know whats left. I have sprayd stater fluid all over. Am i forgetting something what else to check. Mileage is 240000
99 expo 4.6 trouble
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ArtGamer60
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sure sounds like a vacuum leak ... try soapy water ...
It does show signs of a big leak that should be easy to find. I fail to say i smoke tested no leaks. No codes. I also change egr
ArtGamer60
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Including brake Booster ? agreed about vacuum leak . I wonder if it is a crack ? does it do it when it is cold also ?
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I removed the line and covered with my finger at the throttle body. No change
ArtGamer60
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A Crack somewhere , does it do it when it is cold ?
when it cold it is harder to start and surge and worse. When it comes up to temp the surges become a lumpy idle which rocks the truck it is not drivable that way.
ArtGamer60
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timing chain didn't jump a tooth or two ?
I wouldn't think so. When surging when i cover the maf it idles up to2k and drops down to 750 rpm and is drivable. It cruises fine but off idle has hesitation.
1997SCEBFEX
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i'm sure you retraced all your steps, sounds like something is not hooked up/plugged in.
PanHandler.
PanHandler.
Jeff532003
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Going out on a limb here but cracked manifold perhaps? There's an old trick I use on vacuum leaks on motorcycles that can be used on a car as well just be much more careful. Take a propane torch and crack it open but don't light it. Run it over anywhere you suspect there's a leak, intake, manifold, throttle body, egr ect and if the throttle surges then that's where your issue is. In most cases it works better when the engine is warm as metal expands creating a bigger leak.
Good luck.
Good luck.
BANGEREXPO76
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Is it throwing any codes?
P1506 and p1121. I believe p1506 shows signs of vacuum lose or pcm trouble, p1121 because i have the maf partially covered (new tps). I have installed and remove the intake about 5 times now for different reasons( can do it in 1 1/2 - 2hrs now!). I smoke tested again today with a cigar. Had a leak at iac i have been told this is normal ford tsb. I blocked it off and the throttle body leaked at the return springs (dont know if thats normal). With me blowing harder a small leak appeared at the brake booster metal vac line mounting tab. None of these leaks respond to starter fluid. These is the third iac to leak this( 1 factory and 2 after market). I replaced the booster line engine runs the same. Could it b the throttle body?
stamp11127
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I've always used a can of good carb cleaner w/straw to find vac leaks. Spray lightly and wait a second for a change in idle speed. Don't like using starting fluid or propane for safety reasons - more is not always better. Don't spray the EGR valve on a hot engine - they will catch on fire. Been there, done that (a long time ago).
Yes you can have a leaking TB. None of my IAC's have leaked in the past.
Since the intake has been off @5 times have you used the same gasket all along?
Yes you can have a leaking TB. None of my IAC's have leaked in the past.
Since the intake has been off @5 times have you used the same gasket all along?
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I tried reused didnt trust it now has new gaskets through out. This problem started wierd. Wife filled up said no power afterwards. I met her and drove home. With no problems. Got back in drove another mile. Stop and talk awhile would not start. Went got tools hour later fired write up drove home got weak at home. Drained tank and unhooked exhaust ran the same. This was in january. Have had several fill up since no change.
BANGEREXPO76
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Are you sure the TPS is functioning correctly. Is the TPS getting proper power from the harness? Check for a leak somewhere in the air line after the MAF. Its something about that MAF that is fishy to me. Having to partially cover it to get it to run correctly is definately a smoking gun. HMMMMMMMM
Covering half the maf?!
If you are running it without an airfilter it will not get consistent airflow across the sensor and it will be inaccurate. Filter smooths the airflow. Hand is not quite as consistent..
Sorry if I missed this.... did you reset the pcm after replacing various parts. If there was a problem with one of the misc sensors, specially the maf sensor, the adaptive learning may have been skeewed to it's limits. It would eventually relearn but its quicker to start from the base settings.
Just curious...will it start and idle smoothly if you disconnect the maf sensor?? It will default to the failed mass air table which relies on throttle position and rpms. Its a limp home mode for failed mass air sensor. When its initially started it ignores the maf anyways.
If it idles smoothly and consistent I would suspect the mass air sensor/ circuit or vacuum leak. Only because you removed the maf from the equation. If not it proves nothing.... Just my theory
If you are running it without an airfilter it will not get consistent airflow across the sensor and it will be inaccurate. Filter smooths the airflow. Hand is not quite as consistent..
Sorry if I missed this.... did you reset the pcm after replacing various parts. If there was a problem with one of the misc sensors, specially the maf sensor, the adaptive learning may have been skeewed to it's limits. It would eventually relearn but its quicker to start from the base settings.
Just curious...will it start and idle smoothly if you disconnect the maf sensor?? It will default to the failed mass air table which relies on throttle position and rpms. Its a limp home mode for failed mass air sensor. When its initially started it ignores the maf anyways.
If it idles smoothly and consistent I would suspect the mass air sensor/ circuit or vacuum leak. Only because you removed the maf from the equation. If not it proves nothing.... Just my theory
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Covering half the maf?!
If you are running it without an airfilter it will not get consistent airflow across the sensor and it will be inaccurate. Filter smooths the airflow. Hand is not quite as consistent..
Sorry if I missed this.... did you reset the pcm after replacing various parts. If there was a problem with one of the misc sensors, specially the maf sensor, the adaptive learning may have been skeewed to it's limits. It would eventually relearn but its quicker to start from the base settings.
Just curious...will it start and idle smoothly if you disconnect the maf sensor?? It will default to the failed mass air table which relies on throttle position and rpms. Its a limp home mode for failed mass air sensor. When its initially started it ignores the maf anyways.
If it idles smoothly and consistent I would suspect the mass air sensor/ circuit or vacuum leak. Only because you removed the maf from the equation. If not it proves nothing.... Just my theory
I have cardboard between maf and filter. Computer is reset after every sensor change. The engine lopes worse with maf unplugged. Idles smooth maf plugged in and half covered.
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