1986 Ranger - runs rough after driving almost exactly 5 miles

[DangerRanger42]

Hello all, I'm new here so I'll start at the beginning. I bought a 1986 Ford Ranger in June of 2012 on Craigslist for $1000 cash and have been fixing it up and tuning and such ever since (no surprise there ).

But recently I've run into a new problem: when you are driving at first, it runs fine, for almost exactly 5 miles. After that, it starts to shudder a bit, randomly lose power. Soon you start bucking and surging and stalling at red lights, stop signs, etc. And this is with half a tank or more. Keep driving, especially start stop driving, like running errands, and when you try to accelerate it's just vroom-VROOM-vroom-VROOM and then stall. This started about 3 weeks ago.
Now, before your suggestions, let me tell you what it already has: new MAP sensor, EGR valve, PCV valve, under-cab fuel filter, O2 sensor, TPS (may need to be adjusted?) and ignition timing done. My thoughts were that it could be the fuel pump (there are two) or the in-tank filter. I doubt it's a head issue because it's never overheated and I replaced the water pump recently.

So what do you guys think? I'm 18 and still a few months from graduation, so I'm not exactly swimming in $$$. Would a fuel pump or filter issue be a reasonable guess? Or do y'all have any other suggestions?


TL;DR version: 1986 Ranger, drives fine for about 5 miles, then starts to surge and die. No power. Head issues doubtful. 02 sensor, PCV valve, MAP sensor, EGR valve replaced. Maybe fuel pump or filter?

 

[alwaysFlOoReD]

Have you tried pulling codes?
I had the same problems in my 86 and parked it a few years ago. I will have to look into it again as I've learned a bit since parking it. I don't have a solution for you, maybe someone else?
Good luck,

Richard

 

[DangerRanger42]

I have tried pulling codes in the past for a different problem, but was told they have to "catch it in the act" so to speak, due to its extremely primitive ECU. But that was for a much more intermittent problem so I may go and have that done.

Thanks for the advice!

 

[Psychopete]

have you tried restarting the truck when it's warm to see if the problem comes right back? You can catch it, get the engine up fully up to temp and run a KOER test. Anything seen during engine operation is stored in memory, so you can retrieve those, too. No check engine light as 1986 does not have a functioning one, really pulling codes is the best place to start.

 

[MikeR]

I would look at the O2 sensor. Mine a few years ago was having almost the same problem it would stall and run really rich and then go lean and stall. Also while driving it would surge really bad and lack a good bit of power.

 

[DangerRanger42]

When you restart the problem does come back immediately. What is a KOER test? And I will try disconnecting the O2 sensor and seeing if it drives better that way.

 

[adsm08]

I am thinking plug wires may be to blame here. I have had several issues in the last few years that match the given symptoms that were in some way related to the plug wires.

First I would have no power/misfires at random, only after the truck started getting warm (about 5 miles). Turned out the coil wire insulation was weak and it was sparking to the block. Threw in an old (good) one I had laying around and it was fine for a while. Then I had similar problems again a few weeks ago, sound my number 4 wire rubbed through at the plug boot, again sparking to the block. Replaced all with a new set (I was out of spares) and it runs awesome now.