A miss @ idle

[Jim2]

My truck hesitates when I punch it @ idle... it's just for a split second, and then she revs clean to the top end after that.
Also, it backfires once every time I let off the gas for the corners (from redline).

This truck is only for the track, so I don't care about MPG at all.
The track out here is a small, it's a dirt-rally course.
Top speed is never a factor over there, but 0-45 is everything.. so I would trade some top end power for more low end response.

So anyway, here's some more info about it.

-The exhaust ain't stock.. it measures 2-1/2" O.D. at the tailpipe, but I cut it off right after the muffler. The I.D. is 1-7/8" at the bend where I cut it, and there's no catalytic converter.

-It has headers, but I don't know what kind/brand.

-Has an "Accel" ignition box.

-Has what looks like a "K&N" style air filter. (It's kinda dirty, but even when it's removed, the miss is still there)

-I installed a stronger fuel pump in the tank. I guess the inline pump is stock.

-I just replaced the heads and set the valves.

-The fan clutch is jammed up. There's no clutch action. It's like a solid link there..



If anyone can offer some tuning advice, I'd really appreciate it.
I'm a carpenter, so I don't know too much about tuning... but I'm tempted to advance the timing a little more..

 

[Psychopete]

Did you install the right intank pump? It's supposed to be a low pressure pump, 89+ 2.9L Rangers only had a single intank pump, where 86-88 will have the single low pressure pump and high pressure frame mounted pump. Just throwing out some ideas. No reason for anything but factory parts on the fuel system components granted everything else is factory.

Start with checking the fuel pressure, check for vacuum leaks, check engine vacuum, and pull codes from the EEC-IV system. Low vacuum signal could be screwing up MAP signals, just need to do some basic diagnostics to help narrow down what the problem is.

 

[Jim2]

Did you install the right intank pump? It's supposed to be a low pressure pump, 89+ 2.9L Rangers only had a single intank pump, where 86-88 will have the single low pressure pump and high pressure frame mounted pump. Just throwing out some ideas. No reason for anything but factory parts on the fuel system components granted everything else is factory.

Start with checking the fuel pressure, check for vacuum leaks, check engine vacuum, and pull codes from the EEC-IV system. Low vacuum signal could be screwing up MAP signals, just need to do some basic diagnostics to help narrow down what the problem is.

Thanks Psycopete,

The pump that I put in the tank is more powerful than what was in there before. I guess the previous owner was planning something, because when I got the truck, it had a bunch of extra parts inside.
Among those parts, I found two internal pumps and one frame pump. (all used parts)

Here's the 2 pumps side by side. The one on the right is very much stronger..

I tested those two internal pumps in a cup of water, just to see what's what. Here's what I found;
Original pump: http://www.youtube.com/watch?v=FrgkpQERhMc
Bigger pump: http://www.youtube.com/watch?v=UwQ9UJw4uMc

So I used the bigger pump. I had to shorten the stem that it connects to, but it's in there now.

At that point, I was struggling to get fuel pressure (only had about 12psi), so I figured I gotta try something, right?... but it didn't fix the problem.

The problem turned out to be one little ground wire under the hood... the black/green wire that goes from the fuel pump relay to the battery ground. It was disconnected and hidden among a bunch of abandoned wires from the AC system.
After that simple little fix, my pressure came right up. At idle, it sits @ 31 psi.

fwiw, I tested the frame pump too. It works, but doesn't look quite as strong as that in-tank pump. I replaced the fuel filter too.

--------------

... check for vacuum leaks, check engine vacuum, and pull codes from the EEC-IV system. Low vacuum signal could be screwing up MAP signals, just need to do some basic diagnostics to help narrow down what the problem is.

I looked for vacuum leaks, but I don't have a tester yet.. A couple hoses are plugged, and everything else looks connected.. but I don't know what does what...

I set the timing according to spec, 10 BTDC, with the spout pulled.

I'm wondering about the back pressure... with the headers and oversized exhaust, I'm trying to understand what effect that would have on everything.. ??

She revs clean at redline, but lacks a little something down low.

The vid below is from the main event last weekend. It's shaky, but you can hear the engine.
Towards the end of the vid, we overheated.. but I had to keep it idling for 15-20 minutes before the race (because I needed a jump-start), and my radiator has a slow leak.. we got off before doing any major damage though.. she fired right up the next day.
http://www.youtube.com/watch?v=xV1meYwA2k0

 

[FordRanger1991]

if all you care about is 0-45 put some lower gearing in it. Also you could always go with an electric fan... that would be less stress on the motor than a locked fan lol if you dont care about that engine lasting long... which i cant image you do because of what you put it through... then set the timing to 12 and run some premium with some octane booster each race.
i would leave your exhaust system alone if you don't have to pass any smog tests
go to this web link for some other upgrade info by natedog there seems to be some good stuff on the post on the bottom of the page titled "what works"

http://www.therangerstation.com/forums/showthread.php?t=10

 

[Jim2]

if all you care about is 0-45 put some lower gearing in it. Also you could always go with an electric fan... that would be less stress on the motor than a locked fan lol if you dont care about that engine lasting long... which i cant image you do because of what you put it through... then set the timing to 12 and run some premium with some octane booster each race.
i would leave your exhaust system alone if you don't have to pass any smog tests
go to this web link for some other upgrade info by natedog there seems to be some good stuff on the post on the bottom of the page titled "what works"

http://www.therangerstation.com/forums/showthread.php?t=10

right on, thanks for that link. I came across it once before (while searching something else), but this time I read the whole thing. Lot's of good stuff there!

..if you dont care about that engine lasting long... which i cant image you do because of what you put it through...

I guess I can understand why you would think that (based on that vid)... but really, I do care.
I hope to get as many races as possible out of this one.. this is a low budget operation.. but I had to push it like that because there was no bottom end response.

When I first set the timing, I considered advancing it a little... but I didn't want the heads to crack again.
Also, I wasn't sure how much it would help because the computer controls that stuff too..?? I still have a lot to learn about tuning..

After reading that whole thread, my plan is to set the timing to 12, run straight water thru a cooler thermostat, and find a 58 mm throttle body. If I can gain a little low end response, maybe I won't have to redline it like that.

Thanks again!

Jim