'90 4.9L 6 cyl PCV location, surge
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Joined: Apr 2004
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From: Alaska
'90 4.9L 6 cyl PCV location, surge
Hi all,
I just bought a '90 F150 with the 6 cyl 4.9 L engine, 80K miles. It runs well, except for some hesitation and surging that seems to occur when the throttle is slightly opened, but not when I'm accelerating hard. I also noticed an oil leak on the driver's side towards the back of the engine. It seems to be leaking from the cylinder head gasket. I installed a new air cleaner, but no difference. I thought I'd change the PCV valve, but I can't find it! Do I have to remove the intake manifold? Where is it? Would this oil leak be a big job to fix? Any thoughts on what may be causing the surging? Possibly TPS?
I just bought a '90 F150 with the 6 cyl 4.9 L engine, 80K miles. It runs well, except for some hesitation and surging that seems to occur when the throttle is slightly opened, but not when I'm accelerating hard. I also noticed an oil leak on the driver's side towards the back of the engine. It seems to be leaking from the cylinder head gasket. I installed a new air cleaner, but no difference. I thought I'd change the PCV valve, but I can't find it! Do I have to remove the intake manifold? Where is it? Would this oil leak be a big job to fix? Any thoughts on what may be causing the surging? Possibly TPS?
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Joined: Apr 2004
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From: Alaska
update
I think I found the oil leak - oil pan gasket. Also found the PCV valve way at the back of the engine - found it by following the hose from the right side. Wasn't hard to change once I found it. Old valve and hose were pretty clean, rattled fine, so I don't think that was causing my surging problem. I also changed the plugs - put in Autolites. The old plugs looked pretty good though, just a bit of tan deposits. I changed the fuel filter (my arm got a good unleaded 87-octane shower in the process, as I didn't have the special tool to depressurize the fuel system).
It may be my imagination, but I think the surging/power loss has decreased some, but it's still there - right after I upshift and am lightly accelerating toward 2000 RPM. I think I'll check the TPS resistance next, but I just have a cheap multi-meter and according to Chilton, there is a large range of acceptable values (I think ~0.6 - 1.3). Any other thoughts on this problem?
It may be my imagination, but I think the surging/power loss has decreased some, but it's still there - right after I upshift and am lightly accelerating toward 2000 RPM. I think I'll check the TPS resistance next, but I just have a cheap multi-meter and according to Chilton, there is a large range of acceptable values (I think ~0.6 - 1.3). Any other thoughts on this problem?
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Joined: Sep 1999
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From: Ventura, California
There are 3 likely causes of the problem you are experiencing.
1) Dirty injectors. Go to Kmart, and buy 2 of biggest bottles of injector cleaner they sell that comes in a gray plastic bottle with a gold colored cap. Get your tank almost empty, and add 1 entire bottle, and 4 gallons of gas. Drive it for a day or two, and see if the problem diminishes. If it does, then it's your injectors. Repeat the process, and your injectors will be as clean as they're gonna get. If it's not good enough, then replace the injectors.
2) EGR problem. Disconnect and plug the vacuum line that goes to the EGR valve. See if that fixes the problem. If it does, you will need to make a restrictor plate and install it inbetween the EGR valve and the intake. I will give you more detailed instructions if you need them.
3) Bad TPS. As far as actually testing your TPS, this is best done with a DMM that has a bar graph, but any MM will work. Disconnect the TPS from the harness, and attach your meters pos. lead to the Green wire pin, and the neg. lead to the Black wire pin, at the TPS connector. Set your DMM to ohms (4k scale), and rotate the throttle slowly by hand. Observe the DMM. It should increase and decrease smoothly with the throttle opening and closing. If it jumps around at all, replace the TPS. If it passes, before you hook it back up, turn the key "on" and measure for voltage (20dcv scale) between the orange wire and the black wire at the harness connector. It should be 5.0vdc (+/- .4vdc). Turn key "off".
Bring engine to operating temp., and shut off. To adjust the TPS after it's in place, you will need to access the green wire while the TPS is connected to the harness. You can try to backprobe it with a DMM lead or pierce the wire with a very small safety pin. Attach the DMM pos lead to the pin (or backprobe), and the DMM neg lead to good engine ground. Turn the key "on". Set your DMM (to 20vdc scale). With the throttle closed, at idle, the DMM should read no higher than .95 vdc and no lower than .75vdc. If it does not fall within this range, loosen the two TPS mounting screws and rotate the TPS as best you can until you reach that range. Sometimes the plastic openings on the TPS need to be widened to allow more movement. If and when the TPS falls within that range, slowly rotate the throttle, while watching the DMM, to WOT. It should rise smoothly, and read over 4.5 vdc at WOT.
Take care,
~Chris
1) Dirty injectors. Go to Kmart, and buy 2 of biggest bottles of injector cleaner they sell that comes in a gray plastic bottle with a gold colored cap. Get your tank almost empty, and add 1 entire bottle, and 4 gallons of gas. Drive it for a day or two, and see if the problem diminishes. If it does, then it's your injectors. Repeat the process, and your injectors will be as clean as they're gonna get. If it's not good enough, then replace the injectors.
2) EGR problem. Disconnect and plug the vacuum line that goes to the EGR valve. See if that fixes the problem. If it does, you will need to make a restrictor plate and install it inbetween the EGR valve and the intake. I will give you more detailed instructions if you need them.
3) Bad TPS. As far as actually testing your TPS, this is best done with a DMM that has a bar graph, but any MM will work. Disconnect the TPS from the harness, and attach your meters pos. lead to the Green wire pin, and the neg. lead to the Black wire pin, at the TPS connector. Set your DMM to ohms (4k scale), and rotate the throttle slowly by hand. Observe the DMM. It should increase and decrease smoothly with the throttle opening and closing. If it jumps around at all, replace the TPS. If it passes, before you hook it back up, turn the key "on" and measure for voltage (20dcv scale) between the orange wire and the black wire at the harness connector. It should be 5.0vdc (+/- .4vdc). Turn key "off".
Bring engine to operating temp., and shut off. To adjust the TPS after it's in place, you will need to access the green wire while the TPS is connected to the harness. You can try to backprobe it with a DMM lead or pierce the wire with a very small safety pin. Attach the DMM pos lead to the pin (or backprobe), and the DMM neg lead to good engine ground. Turn the key "on". Set your DMM (to 20vdc scale). With the throttle closed, at idle, the DMM should read no higher than .95 vdc and no lower than .75vdc. If it does not fall within this range, loosen the two TPS mounting screws and rotate the TPS as best you can until you reach that range. Sometimes the plastic openings on the TPS need to be widened to allow more movement. If and when the TPS falls within that range, slowly rotate the throttle, while watching the DMM, to WOT. It should rise smoothly, and read over 4.5 vdc at WOT.
Take care,
~Chris