I'm a newbie to the forums and I searched the history and think found what the problem with my truck (86 F150 2wd, manual trans) .

I believe my truck has the computer going into "open Loop" situation...she starts/runs fine and after a bit of driving (never the same amount) she starts loosing power, then bucking and misssing and sucking down HUGE amounts of fuel. Also she seems to do this on cold wet days (snow/rain)...then again that's the reason I'm driving the ol truck.

I have previously done the ususal things: rebuilt carb by a shop, new rebuilt distrib w/ module, spray tests for vacuum leaks, checked the choke to be sure, plugs, wires, rotor, cap w/i the year

So anyhow the previous post said to go to non-feedback carb, also Duraspark system, etc.. although, still a few questions that will help me decide which way to go.

So for the simpliest and cheapest solution:
1. what parts need to be changed?
2. what approx cost can I expect for said parts
3. In general terms how long should this take?

VS getting a newer truck

Thanks

 

1. well I have an 84 yfa & I checked timing,o2,TPS,MAP, with like symtoms not as bad as yours. (replaced TPS,O2) I found the carb to be a big part of it all. 7-10 MPG unbearable odor at idle. so I played with the idle screw & no response. removed the top & adjusted the metering rod to the other end & it put me back on track. so my point is keep the setup you have & just call the shops & get a diagnose or if you can remove your eng. comp. & have it checked. I bought a Offy intake & headders ready to reinvent my truck but changed my mind after it all came together to run very well much to my suprise. I am leaving it "as is"
   just get some help & dial in that carb. they work good.
2. also pull a spark plug after a drive (operating temp.) & see the color. & then let it idle for 10 mins & check again. this info will help you to get the help you need.

 

Hey thanks for posting mmckee...I've been at the point of considering a newer truck b/c of all this and no good debug routes...chiltons sort of sucks on this.

My MPG has been just as bad. Having had the carb rebulit by a good carb shop w/i the year I tend to think its the computer or one of the inputs though.

1. ANy sugguestions who can test the computer?
2. What should I check on the TPS...is that the weird solenoid thingy on the back of the carb that pushes on the throttle linkage? Any ideas to check whether that's good or bad??

3. So the O2 and TPS are the biggest culprits to screwing up the computer??

Thanks again

 

pull the codes with a code reader/scanner or run the engine self test. you should also try disconnecting the battery cables...this resets the computer, just like rebooting your desktop computer. run a search for pulling codes and the link to the self test page will come up I bet. you can do this yourself with just a jumper wire, it blinks the computer fault codes through the check engine light. this is the best way to find what's really wrong instead of throwing $$$ at it.

 

Thanks for the tip...This might be a stupid question ( I haven't owned the truck for that long) but, where is the computer...I take it its under the dash. Based on that and the year of the truck I didn't think that it had codes (i.e. OBD1).

 

Your truck is Way Before OBD1. It's EEC IV, just like my 90 F150. But your truck doesn't have the Check Engine Light. You can still pull the codes very simply. Go to this link, print it out and read the part about pulling codes on vehicles without CE lights.
http://fordfuelinjection.com/files/self_test.pdf

 

So for the simpliest and cheapest solution:
1. what parts need to be changed?

Depends on the diagnosis of whats wrong.
2. what approx cost can I expect for said parts
ditto...
3. In general terms how long should this take?
However long it takes.

Not trying to be smarta@#...But you have to diagnose *first*, and then replace what is wrong. This is ultra important with a computerized system. You will need the proper manuals, in order to know what, how, and what values to check for. The manual will tell you how to check the computer. On that year, it's quite possible no scanner is needed, but I'm not sure.. Shooting in the dark, or just replacing parts *****-nilly, is no way to live. With your
current results, I probably don't have to tell you that...There is no reason to change to a non-feedback carb, or the ignition, for that matter. Just fix what you have , so it operates properly. You start changing all that stuff out, and you will end up in worse shape than you are now. Probably will flunk any emissions test's also, if those are required in your area...There are many parts which can throw the computer off. Temp sensors, map sensors, TPS, etc,etc,etc...You will want to test each part of the system to make sure it is working correctly. If you don't have the books/manuals, test gear, or maybe even experience, to be able to properly diagnose the system, I strongly suggest taking it to a *qualified* shop for diagnosis. It would probably save you money in the long run.
I *never* replace a part without first verifying without a doubt that it is bad. Fortunately, with most of the sensors, etc, this is easy to test, if you have a VOM. IE: TPS is easy to check. Of all the sensors, the o2 is probably the hardest to *accurately* check...They can *test* good, but still be sluggish, etc...I always leave the o2, until nearly the end...If all else is known good, and the car still acts up in a manner that points to a sluggish o2, I'll then just change it out at the end. Many of the newer computers will flag the o2 sensor if it falls out of range. But many of the older systems will ignore it, and assume it's working as normal, even if it's sluggish. When thats the case, you will usually be running rich.
You say you are staying in open loop???First thing to check are the temp sensors, after first pulling any codes off the puter...If the temp sensor is bad, and the car thinks it's always cold, it will stay in open loop till the cows come home.. MK

 

Thanks tmcalavy for the link. I really appreciate it. My manual didn't have anything about this.

nm5k: As stated in the earlier posts I have it 'narrowed' to the wacky carb feedback system . Since I was new I wanted to looking into the history first based on what I had read in previous posts it seemed that this(i.e. replacing distrib, carb...) was the "way". Now mind you that was using the search function and I am a newbie to this forum...but not to forums in general....but the "search" function here didn't quite narrow things down.

Thanks for the advice on what sensors....I'll check the temp sensor and the others in the order you provided. That really helps!

I have debugged multiple different fuel injection systems before so I'm familiar with the process. Since this system is not only carb and not fuel injection and has all this egr, air pump, etc stuff that fuel injection systems don't I was just looking to see if someone could point me in the direction of the traditional culprits if there was one with this system.

Thanks again

 

The mid-eighties computers used a direct ground reference to the battery negative cable. If a lazy prior owner changed the ground cable without somehow dealing with the extra small cable on the battery cable, then you have no computer ground....instant open loop mode and you can't pull codes either. My '84 was this way when I got it.....

Brian

 

First, a question. Were the "usual things" done in response to the problem in question, or did the problem come on after one or more of those jobs?

As mentioned before, start with the codes.

EGR function should be similar to that on an FI engine. Air pump is downstream of the engine and won't be involved here.

"Starts, runs fine." Either it coming off fast idle removes the problem's disguise or some component begins to fail as it warms up. you can tell the difference just by observation. Either the problem correlates with with coming off fast idle or not. If so, you're probably looking at carburetion.

"after a bit of driving (never the same amount)..." Probably not the fast idle thing. If not, my money is on an ignition component.

The distributor shaft mounted TFI ignition module is infamous for partially failing and being sensitive to heat and moisture. Also, when I replaced mine, I had to replace it twice, because the replacement part was bad out of the box!

You didn't mention the coil in your list of checked/replaced parts. I have heard an iffy coil can be temperature/heat sensative, too.

The computer is under the dash. More importantly, the self test connector is on the right side of the engine compartment, near the battery. If this is redundant to the link provided, I apologize. I didn't follow it before starting my reply.

IMHO, Chiltons just sucks. You might try Haynes. It seems be me to be a little better.

Good luck tracking this down. MK is right. Can't answer any of your original questions until you get a specific diagnosis. When you do, the answers will come pretty easily.

 

The small chiltons are fairly lame overall. But the larger chiltons "care care manuals" are quite a bit better..The trick is finding one for the truck...So far, I haven't seen one for the old ones I have, but they may have them...I had one for my old monte carlo, and also a camry, and it was pretty good as far as emissions gear, puter, etc.
Yep, it's hard to be an armchair quarterback in a case like this...
It could be anything from a sticking float valve, frayed wire, bad sensor, etc, etc, etc, It's all a guessing game, until it's actually checked out in person.
Unfortunately, we can't do that online...
Does it blow black smoke and seem obviously rich when it acts up?
It would probably do that if the float were sticking, or it had a choke problem. A super lean condition IE: fuel pump failing, or super clogged filter, "will usually cause a real funky smell from the engine, and exhaust. Also can white coat plugs if the combustion temps go real high, from being so lean. Super rich will leave black sooty plugs. Just from the description, a sticking float could be as likely as anything...That would make it buck and stumble, idle rough, and drink gas like a fish...But....Usually you would eventually see gas pouring from the base of the carb, onto the manifold....Just knowing if it's too rich or too lean, would help a lot...Also any puter codes...MK

 

again thanks. I'll answer your guys questions.

Castman: Thanks, so EGR and airpump won't be a real factor here. (non of the FI systems I've before have had this airpump thing)

I'll take #2
"after a bit of driving (never the same amount)..." Probably not the fast idle thing. If not, my money is on an ignition component
This is what occurs and at times it never occurs?

Replaced the distrib(rebuilt) and module a few months ago...module was bad and could be removed easily and part of the dist housing hosed so just got rebuilt...easier/cheaper

So your saying the TFI could be bad intermittently?

I've done the basic resistance checks on coil...ok but they wouldn't show what you mention...intermittent failure...But the temp sensitivity is not happening when it that hot...besides if I pull over let it idle for 5 mins fiddle around with stuff she settles out and I'm down the road again w/o probs for a little while then all over again. The temp sensitivity has been cooler air temps or more specifically WET weather

nm5K: never blows black smoke when acting up...runs rich though. Next time I start (i.e. next day) starts fine power back (peppy) blip the throttle blows out the carbon...I have a black snow bank to prove it

Isn't overflowing gas either...did that before carb was rebuilt

Brian: I'll check ground cable...who knows w/ this truck's history. I take it this is supposed to go directly to the computer? (i.e. through firewall)

Castman: Thanks for computer and plug location(not redundant)!! now I'll be able to check it sooner.
All: I'll check codes at earliest possible time

Thanks

 

Hey After the responces try one real simple thing....

Remove the air cleaner

and Wiggle the top of the carb. The YF uses a 2 piece base and 90 percent of the time it will intermittantly suck air and run like crap.

There is no way to tighten it either on the manifold as the bolts come up from the bottom. I have found that this is a good way to pick up cheap rough running 300s in mid 80's trucks that drove the PO nuts. simple fix...

O2 sensor suddenly reads lean and feedback dumps more fuel in to compensate...Bad mileage and black smoke bucking and kicking. and no memory code is typically thrown.

Garbz

62 F250 UNI 300 with SROD
86 F150 4x4 Goat truck finally dies after 310k (Body rotted off the frame...Motor transplanted into 62
66 Super Crew 460 C6
63 Pro Street Uni 410 Merc C6

 

I have an 84 I6 with the TFI IV ignition and the feedback carburetor and I have had many of the same problems described here. No one thing was the magic bullet to completely fix the problem it was a combination of things that eventually corrected things.
Codes, Codes are nice to see what is working but I get very little information from pulling the codes. All you need to get the codes is a short jumper wire and a cheap analog voltmeter.
You will need a good shop manual best is the original ford manuals you can find a whole set on ebay for about $35.00 and are a big help.
Connectors are a problem on these trucks they get corroded and are sometimes hard to get apart. If was starting all over again I would start by buying some dielectric grease. This is conductive grease you can get it at the auto parts store in a tube from Locktite. Take every connector apart inspect them and apply the grease to each. I used a small points file (Thin and narrow) to clean the spade connectors.
I had a really corroded connector to the TFI module that was causing intermittent problems. Also the connector you disconnect to set the initial timing. After months of intermittent problems I finally replaced the TFI connector with a new one from rockauto.com it was a splice in connector worked great. Problems gone! Also there was some stripped wires where the bundle goes from the TFI to the Harness three of the wires are shielded one of these is the yellow wire to the single connector plug. It was stripped where it enters the shield under the tape where it goes into the harness. I was able to tape this up.
Remove the plug from the computer and coat the pins with the grease.
This engine will never run right unless all sensors are working. This is not like an older engine that you can tweak. The computer is scheduling the amount of fuel to be used based on the sensor inputs, so garbage in = garbage out.
Set the timing this is important on this engine mine is at 10deg before TDC
You can use a timing light or you can cold time it.
(Cold timing! Put a ratchet and socket in the flywheel nut. Remove the distributor cap; rotate the engine in the direction of normal rotation manually with the ratchet. Watch the timing mark bring the engine to the timing mark. Observe the distributor rotor at TDC rotor should be pointing toward the fuel pump. Remove the #1 Plug ground the #1 plug to the engine block. Loosen the distributor hold down nut. Remove wrench from flywheel. Turn on ignition but do not engage starter. Rotate distributor slowly until you see the plug fire. Rotate back and forth until play with it until you get it where the plug just fires. Tighten the dist hold down nut. You are in time. Replace spark plug and cap)
Start engine.
If you have a timing light the timing should retard to about 30 deg BTDC and advance when you rev the engine. This will tell you the computer is working. If it is not working the timing will beat 10 BTDC. This could be the one pin connector at the TFI module.
That cylinder thing on the throttle linkage is the idle actuator. It is a small electric linear actuator controlled by the computer to adjust the Idle. It has to be working or the engine will never idle right. Test it with 12 volts on the plug two pins are ground two are power. You just reverse polarity to move it in and out.
Oxygen sensor, my truck has a green (single wire) that goes to the computer
I pushed a pin thru it and measured to ground with a digital voltmeter it should read about .5 to 1 volt. With engine warmed up.
Anyway there are a few things to try.
Good Luck.

 

finally....someone with my problem.i don't feel so alone now.

I have been battling this same symptom on my 1995 FI engine.
Exact same.

I will read through again slowly and try everything you all posted. (except Carb stuff).
But, I see black smoke during start and the smell is rich.