4.9l stalling and surging

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tengraver
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4.9l stalling and surging

Post #1 by tengraver » Sat Jul 07, 2018 8:28 pm

I recently picked up a 1987 F-150 with a 4.9l, manual tranny, 4x4 (first year of EFI on this engine). It runs great on cold start but hot it gives me some trouble. It will start right up but then begin to surge up to about 1500 RPM and then fall back down so low it will usually stall. When it behaves like this I will usally smell some oil burning but it can't be a lot - I haven't had to add any since the last oil change. After a few minutes back on the road it returns to it's old self, but I'm getting to where I hate to shut it off if it's only going to be for a few minutes. I have replaced the plugs, wires, cap, rotor, and ECC, new oil change and filters...amazingly, all that cost was about $190 - my MB costs more than that for an oil change, lol. All that work needed to be done, but didn't help the problem. I don't know how to read codes on this truck because it is pre-OBD. I know a lot of the older models had procedures for reading codes, so I could use some help in diagnosing my problem. Fuel injectors? Throttle position sensor? Coil? Distributor? I'm not sure what sensors this thing even has. Thanks in advance.

94f150rules
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Re: 4.9l stalling and surging

Post #2 by 94f150rules » Tue Jul 10, 2018 5:36 pm

Welcome to the forum, when I got my 94 it ran a lot like yours. start tracing out your Vacuum lines and if any of them look a little dry or brittle, have small cracks, or are just torn replace them. The line is very cheap, another thing to check is EGR operation mine was stuck open and causing a rough idle. with the truck running stick your hand into the back of the EGR valve and squeeze the diaphragm this will open the EGR and the truck should run terrible then when you let go it should get noticeably better. If it doesnt change replace the EGR and clean out all the carbon build up in the ports. Next thing to try is start the truck and get it warm, then with the engine running get a can of carburetor cleaner and spray where the upper and lower manifold meet, then spray around where the lower manifold meets the head, and at the base of each fuel injector, check around vacuum hoses, the throttle body gasket and if the engine runs different in anyway, you probably have a vacuum leak there. Next take the air cleaner hose off of the throttle body and open up the throttle look for a carbon ridge near the throttle blades, sometimes it gets so thick the throttle doesn't close all the way and it throws the computer off. Use a can of throttle body cleaner and spray the carbon then use an old tooth brush to scrub the whole throttle body as far back as you can go and spray it all out you want it as close to clean as you can get. After that your truck will be a little flooded so hold the gas pedal to the floor and crank the engine until it starts then let off and it will burn off all the cleaner. You can also clean the idle air control valve that helps with the idle, its only held in with 2 bolts, it will need a new gasket once removed, but basically spray that all out with throttle body cleaner and spray out the bores that go into the throttle body to. Doing these basic and CHEAP things made my truck run much smoother and more efficient, not to mention it kept a simple problem from looking like a larger problem. After all this your truck should run significantly better, and if it doesn't check your timing, and if it still doesn't you can start replacing parts. Since your spark plugs are new you can pull them out one at a time, they should be a light blackish color (google proper spark plug color) if any one of them is very white you have a vacuum leak or bad injector, if any is dark and smells like gas you have a bad injector, low compression, a defective/cracked plug or wire, or a leaky injector, and if its a black oily plug you have a busted ring.

Harte3
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Re: 4.9l stalling and surging

Post #3 by Harte3 » Tue Jul 10, 2018 10:36 pm

https://www.troublecodes.net/ford/

There might bne something in that article to help you with checking codes.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

tengraver
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Re: 4.9l stalling and surging

Post #4 by tengraver » Wed Jul 11, 2018 10:55 pm

I did run across these same test procedures on Youtube. I tried them and didn't get any blinks, flashes or pulses. Don't know why...I checked for continuity on the contacts concerned and didn't find anything wrong. I went ahead and replaced the TPS and Throttle Air contol...no good. It started surging right away - even with a cold engine now!

tengraver
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Re: 4.9l stalling and surging

Post #5 by tengraver » Wed Jul 11, 2018 10:58 pm

@94f150rules

I had just came to the same conclusion when I saw your post! I will begin checking vacuum lines and any sensors attached to vacuum lines. Good advice and it seems like the most likely cuprit. Thanks.

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GPGoverMPG
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Re: 4.9l stalling and surging

Post #6 by GPGoverMPG » Fri Jul 13, 2018 7:34 am

This is kind of out there but, I've retro-fit these systems in the past and the VSS (vehicle speed sensor) can cause surging. The computer doesn't know the vehicle is stopped and it hunts around. The other biggie is fuel pressure and the regulator on the fuel rail. Best of luck.
71 F350 4x4 Super Duty 7.3 IDI
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