94 4.9L Have to hold pedal down for warm start
11-08-2010, 08:27 PM
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94 4.9L Have to hold pedal down for warm start
Hi,
I just bought a very used 94 4.9L and it starts right up when cold. However if turned off while warm, you have to hold the gas pedal to the floor to restart it. I know this is not good for fuel injected engines. Once in a while it dies while idling, but not too often. I replaced the idle control valve today, but it did not help. Any ideas what might cause this?
Thanks in advance,
Jon
I just bought a very used 94 4.9L and it starts right up when cold. However if turned off while warm, you have to hold the gas pedal to the floor to restart it. I know this is not good for fuel injected engines. Once in a while it dies while idling, but not too often. I replaced the idle control valve today, but it did not help. Any ideas what might cause this?
Thanks in advance,
Jon
11-09-2010, 11:25 AM
#3
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I agree with that. What is your temp gauge reading when you restart it "warm?" Typically, when you have trouble with warm starts or when engine is warm and dies, it is likely to be ignition electrical because when hot is when the greatest stress is put on the electrical components and that is when they show the greatest wear. I would say do the electrical tune up. You could test the coil and see if it is good, but a new one from Autozone runs less than 20 bucks. After you give it the tune up, let us know what is going on. My guess with the info given is ignition electrical. Good call on the ait filter too. How about pcv valve and crankcase breather while we are at it too, all cheap routine maintenance stuff. When I get a "new" truck I always change oil, air filter, crankcase breather, pcv valve, air filter, fuel filter, and tranny fluid, plugs, wires, rotor, cap. It is relatively cheap to do all of these things, but at least all the filters and tune up in regard to your problem.
Last edited by walter34payton2002; 11-09-2010 at 11:28 AM.
11-09-2010, 06:38 PM
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Hi,
I haven't gotten to any of those electrical items yet. It failed emissions, so I'm going to go through the egr system and replace the o2 sensor. I read somewhere that an egr system malfunction could cause this problem if the valve does not close. Apparently it's only supposed to open above 2000 or so rpms and if it does not close, it tries to send exhaust gas to the intake when starting. I suppose while I'm at it, I'll address the coils, plugs, etc.
Thank you for the input!
Jon
I haven't gotten to any of those electrical items yet. It failed emissions, so I'm going to go through the egr system and replace the o2 sensor. I read somewhere that an egr system malfunction could cause this problem if the valve does not close. Apparently it's only supposed to open above 2000 or so rpms and if it does not close, it tries to send exhaust gas to the intake when starting. I suppose while I'm at it, I'll address the coils, plugs, etc.
Thank you for the input!
Jon
11-22-2010, 03:19 PM
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I have the same problem with my 94.
I've had it for 2 years and it's always been hard to start when warmed up, but it just failed emissions test this past weekend.
Plan on the tuneup, but don't want to spend on other unnecessary parts if I can avoid it.
How did you make out?
I've had it for 2 years and it's always been hard to start when warmed up, but it just failed emissions test this past weekend.
Plan on the tuneup, but don't want to spend on other unnecessary parts if I can avoid it.
How did you make out?
11-22-2010, 04:54 PM
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Error code scans: https://www.f150forum.com/f10/how-re...es-obdi-10907/
Could be the TPS or even the ECT or ACT sensor(s). http://www.fordfuelinjection.com/
Check your base timing too.
Could be the TPS or even the ECT or ACT sensor(s). http://www.fordfuelinjection.com/
Check your base timing too.
11-23-2010, 08:18 AM
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What were the readings on your emissions? Which parts did it fail?
Mine failed hc and nox at both idle and 55mph. When I replaced the o2 sensor (which you should do yourself if you can, it's easy and you'll save a lot of $$), the 55mph readings all passed, but the idle still failed.
In my case, it turned out to be the throttle position sensor sending too rich a mixture, which was more noticeable at idle than at 55mph.
The tps was only $23 at Autozone, and I had thought of replacing it before reinspection, I wish I had now, however the mechanic said it's not 'plug and play', they have to calibrate it? Not sure.
I would also look at your EGR system. Take the hoses off and visually inspect it. You can run a vacuum test if you have the equipment.
But I would start with the o2 sensor. I've replaced three of them this year and if they are more than 60k old, they need replacing anyway.
Mine failed hc and nox at both idle and 55mph. When I replaced the o2 sensor (which you should do yourself if you can, it's easy and you'll save a lot of $$), the 55mph readings all passed, but the idle still failed.
In my case, it turned out to be the throttle position sensor sending too rich a mixture, which was more noticeable at idle than at 55mph.
The tps was only $23 at Autozone, and I had thought of replacing it before reinspection, I wish I had now, however the mechanic said it's not 'plug and play', they have to calibrate it? Not sure.
I would also look at your EGR system. Take the hoses off and visually inspect it. You can run a vacuum test if you have the equipment.
But I would start with the o2 sensor. I've replaced three of them this year and if they are more than 60k old, they need replacing anyway.
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11-23-2010, 09:55 AM
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There are two different types of TPsensors some are adjustable some are not. The ones that are have elongated mounting holes to adjust output voltage the other one has round holes. When mounting it slide the rotary tang over the throttle shaft and rotate the sensor clockwise to the mounting position. If you don't it can make it idle high on the 302's & 351's,also make sure on these motors that the pigtail is pointed toward the IAC valve.
11-23-2010, 11:24 AM
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There are two different types of TPsensors some are adjustable some are not. The ones that are have elongated mounting holes to adjust output voltage the other one has round holes. When mounting it slide the rotary tang over the throttle shaft and rotate the sensor clockwise to the mounting position. If you don't it can make it idle high on the 302's & 351's,also make sure on these motors that the pigtail is pointed toward the IAC valve.
Your TPS is a candidate, but you won't know for sure, till you run error code scans & if it ain't broke, don't fix it! There have been occasions where it can be bad w/o a code, but very, very rare. (In range, but not accurate in range)
Last edited by ymeski56; 11-23-2010 at 11:31 AM.
11-23-2010, 01:50 PM
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What were the readings on your emissions? Which parts did it fail?
Mine failed hc and nox at both idle and 55mph. When I replaced the o2 sensor (which you should do yourself if you can, it's easy and you'll save a lot of $$), the 55mph readings all passed, but the idle still failed.
In my case, it turned out to be the throttle position sensor sending too rich a mixture, which was more noticeable at idle than at 55mph.
The tps was only $23 at Autozone, and I had thought of replacing it before reinspection, I wish I had now, however the mechanic said it's not 'plug and play', they have to calibrate it? Not sure.
I would also look at your EGR system. Take the hoses off and visually inspect it. You can run a vacuum test if you have the equipment.
But I would start with the o2 sensor. I've replaced three of them this year and if they are more than 60k old, they need replacing anyway.
Mine failed hc and nox at both idle and 55mph. When I replaced the o2 sensor (which you should do yourself if you can, it's easy and you'll save a lot of $$), the 55mph readings all passed, but the idle still failed.
In my case, it turned out to be the throttle position sensor sending too rich a mixture, which was more noticeable at idle than at 55mph.
The tps was only $23 at Autozone, and I had thought of replacing it before reinspection, I wish I had now, however the mechanic said it's not 'plug and play', they have to calibrate it? Not sure.
I would also look at your EGR system. Take the hoses off and visually inspect it. You can run a vacuum test if you have the equipment.
But I would start with the o2 sensor. I've replaced three of them this year and if they are more than 60k old, they need replacing anyway.
NJ State inspection stations don't give details on what failed, just how much it failed. The HCs were over 500 and the CO2 was about 200 at idle, but the readings were way below the limit at 2000 rpm.
It may be the TPS.
Say ymeski56 - I plan on trying the OBD code check, is there a list of what the codes mean?