Smyrna Jeff

I just became the owner of an 87 F150 with the 4.9 six cylinder. I have two issues I'd appreciate input on.

• When first started the engine will idle fine but after a couple of minutes the idle will "surge" down and back up and eventually stall. It will start right back up just fine. If I start it and rev it up slightly for a minute or two it will stay idling fine and drive great. Any ideas on where to start troubleshooting are appreciated
• I've read conflicting info on whether this truck has OBD ..some say it doesn't and other say it does but doesn't have a check engine light to let you know it threw a code. Can anybody clarify that?

Thanks!

midwestbird

Congrats on the truck. I bought a 1990 F150 with the 4.9L last year. Someone else here may be able to tell what your problem is based on the info you've provided, but I did have an issue with a hunting RPM speed at idle. I ended up determining that my fuel pressure regulator was bad (gas in the vacuum line). I'm not saying that is your problem, but you may want to pull the vacuum line off your FPR; if fuel is in the vacuum line, the FPR is bad (which is not to say that if there is no fuel present in the line, the FPR is necessarily good). I replaced my FPG and my hunting RPM at idle went away. I believe your 1987 4.9L uses OBD1. On my truck, the connector is attached to the rear/aft side of the air filter box. I use one of these

tormenta

I had an 87 a long time ago . it's obd 1 . on the driver fender there's a large connector and a small single wire connector . these are for diagnostic . you can get a scanner for it real cheap . when you turn the key on you should see a check engine light until it s running . if everything's ok . if it has dual tanks it has 3 fuel pumps and a reservoir on the frame rail under the driver seat . mine would always act up . if you unplug the sensor by the thermostat it'll speed up and smooth out the idle . a 20 dollar Chilton manual will help a ton . with some care I 've seen over 300k on those engines .
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Smyrna Jeff

Steve83

OBD-1 was a rare GM protocol, but the name is frequently MISused for any system before the global OBD-II standard. These trucks use EEC-IV, and it DOESN'T require any scanner to read codes. Most scanners sold for EEC-IV don't work reliably, so I recommend you return that one ASAP for refund. This caption explains how to read codes:


(phone app link)

But even on modern vehicles, codes are not the crystal-ball most people think they are. On these early trucks, codes rarely help with such a vague symptom as surging idle. Start with thorough maintenance, including fuel system cleaner (I like Berryman's B-12 pour-in, & Chevron Techron) and BATTERY TERMINALS. Click this & read all the captions:


(phone app link)

I also highly-recommend that you get a Haynes manual & read it cover-to-cover at least once:


(phone app link)

Smyrna Jeff