So my truck has developed a problem with starting. When Its started cold you can feel it and hear it miss firing and shaking really bad and will die if I don’t keep it revved up.Eventually after it warms it will smooth out and run absolutely perfect perfect. but after driving it I can shut it off for just a couple minutes and restart it and it will do exactly as it does when it’s cold. Eventually after a few minutes again it will run absolutely perfect. My first thought was coolant temperature sensor which I replaced. Did not solve the problem. Since then I have changed the fuel pressure regulator. The coil. The ignition control module. And even the idle control valve. It has a newer computer and the engine has 25,000 miles on it. I’ve checked for loose connections and vacuum leaks which I haven’t been able to find any. It seems to me I have changed any sensor that would be involved with fuel air Ratios back to the computer. It’s driving me crazy I absolutely can’t figure this one out especially since it doesn’t cold and hot when restarting. It’s like something has to adjust itself as it runs. It does smoke a little during this process but I’m assuming that’s just because of all the gas and stuff that’s probably not getting burnt. Any ideas would be greatly appreciated because I can usually fix just about anything but this one has me stopped. Thanks

 

Welcome to the forum

You replaced the ECT sensor correct?
Not the ECT SENDER, which is for the dash board temp gauge only

One thing that all startups have in common is the computer is in Open Loop when it first boots up and engine is started
It is using 4 sensors
ECT sensor, engine temp
IAT sensor, air temp
MAP sensor, air flow
TPS(throttle position sensor), drivers input, gas pedal

In Open Loop computer is using pre-set air/fuel mix tables in memory, no calculations
Computer is programmed for 2.9l LITER engine(assuming thats what you have)
So it knows EXACTLY how many LITERS of air are coming in at any RPM and throttle position, thats just math, which is what the computer was made for
The sensors are there to fine tune the air/fuel mix

ECT sensor sets Choke mode, rich mix, high idle, when engine temp is under 150degF
If you are not getting high idle on cold start then check ECT sensor again and also IAC Valve, computer uses IAC Valve to set idle RPMs, also to get max air flow for start up

The O2 sensor doesn't work cold, so when engine is at 150degF is when computer switches to Closed Loop and uses the O2 sensor, it seems Closed Loop is when engine Runs OK?

Closed Loop is when ECT sensor reports coolant is over 150degF, or 1-2 minutes after startup if ECT sensor is above 150degF at start up, restart
The O2 sensor needs to be above 650degF to work correctly, so even if engine is still warm the exhaust won't be so computer waits a minute or two for O2 to heat up again

Open Loop does have a memory that can offset its programmed tables, this is to allow engine to age gracefully, lol.
But sometimes you need to clear this memory if there were problems
Unhook either battery cable
Turn on head light switch, this drains capacitors in computer, count to 3 and turn head light switch off
Hook battery back up

Try a restart,

I doubt that will work but FREE to try

Only reasons I see for your issue are ECT sensor, IAC Valve(clean it) or Computer is failing

 

I have replaced the the coolant temp sensor for computer, the idle control valve and the map sensor. I also replaced the computer just because it was only a hundred bucks. nothing has worked. Like I said what really confuses me is it will do it even with the engine warmed up and shut off just for a couple min.the temp drop would be minimal but yet it does it and will be perfect after a couple minutes. This iat sensor. Is this the one on the side of the intake manifold between idle control valve and map sensor. It’s the only thing I havent replaced. It’s a strange one. I can fix anything on this truck so it’s frustrating I can’t track this one.

 

This is a 2.9l V6 right?

One thing I didn't think of was the EGR system, I think 1986 2.9l may have one.
IF(big if), the EGRs vacuum solenoid was failing it could allow some vacuum to pass on startup, causing the issues
Just to take that off the table unplug vacuum hose from EGR and plug it,
See if it makes a difference

Open Loop happens when computer first boots up, temp doesn't matter, computer is always in Open Loop when it starts

How long it stays in Open Loop depends on temperature, but minimum is 1 to 2 minutes after start up, max is about 8-10 minutes or it will set a code that engine is not warming up enough
It is timer based

There are no more "new" parts, just FYI
There are tested parts and untested parts now, you can chase your tail for days thinking "new" means "it works", lol, been there done that
You can pay for Motorcraft parts which are tested, but cost an arm and a leg compared to 3rd part parts

It would be nice to be back in the '60's/'70's when "new" meant "tested and passed", but labor is too expensive now so..........we have warranties, which means "you test it, and we will replace it, if it doesn't work"

It is frustrating because you have done a good job going through the systems that could cause your symptoms, and nothing worked, and it should have, so..............

You need to take away the assumption that a "new" part takes that item off the table as the cause, like it should, unless the new part also doesn't work



IAT sensor would be a long shot but worth testing
ECT and IAT sensor are the same as far as testing, they both get 5volts at key on and then send back .5v(warm) to 3volt(cold)
Voltage goes down as sensor heats up
You can use a sewing needle to pierce wires to test voltages

MAP sensor should be on the firewall, small black plastic box with vacuum hose and 3 wire connector
It gets the same 5volts from computer as the ECT and IAT
But you need a frequency meter to test it
As long as its getting 5volts and vacuum hose is OK I would just assume MAP is OK, they rarely have problems, and problem wouldn't go away



IAC Valve is a Control not a sensor
Remove IAC Valve and plug in its wires
turn key on, computer will open IAC Valve all the way for start up
Look inside at the valve and unplug the wires, you should see IAC Valve close, it only moves maybe 3/8" but moves
Plug wires back in, and watch it open
Repeat as you see fit to know its working

IAC Valve is a 12volt solenoid and spring setup, with no voltage spring holds valve closed
At key on IAC Valve get 12v from EEC Relay, computer controls the Ground wire
At boot up computer grounds IAC Valve so it opens all the way for max air for start up
After start up computer Pulses the Ground, which lowers the 12v down to 8volts or so to set idle RPMs
This method to set idle is accurate to +/- 3rpm, so very precise way to set idle RPMs

 

Thanks for the info Ron I will just keep working. One thing I did when I put a new engine in it two years ago was replaced the computer with an 88 so that I could eliminate the EGR system. End it has ran absolutely perfect sense I did that. This problem just started a couple months ago. And I have addressed every sensor that should be important during start up. But like I said It’s confusing because it’ll basically do the same thing even when it’s warm. Start it cold or warm it up go to the store it’ll run perfect go in the store for two minutes come out and it runs like crap for a few minutes and then runs perfect again even though it was pretty much warmed up to begin with. I will just keep looking

 

Have you tried to check for codes in memory?
How -to here: https://therangerstation.com/tech_library/OBD_I.shtml

If you have a spark timing light check spark advance on start up and then after engine starts to run better
Spark "vacuum" advance is done by the computer via the SPOUT wire
TFI module does RPM advance only, so if you remove SPOUT Connector for startup and engine runs better then computer is setting wrong spark advance in Open Loop


Have a look here: Ford EEC-IV

Pop the top on the extra computer and look at the circuit board
The 3 Blue capacitors do start to leak after 20+ years and cause different issues, but basically poor running is the symptom, lol

This effects all older computers

 

Had O’Reillys hook up their OBD1 Tester. Didn’t really pull any codes except for K0e0 1606. Couldn’t find anything for that does anybody know what this could mean

 

Actually I did find something about ECM control relay. Seems to me that if that was a problem that the ECM won’t be working at all maybe I’m wrong is this a possibility

 

1986 uses 2 digit codes and no 0's 1-9 numbers only

What engine do you have, 2.3l 4cyl or 2.9l V6?

16 is a code but depends on what engine

OBD1 testers are hit and miss on 1988 and earlier computers, 1989 - 1994 seem to be better

The test light(or volt meter) method is more reliable

On-board-diagnostics(OBD) didn't actually have a mandatory standard until OBD2, 1995 and up Rangers, Ford did have its own standards prior to that but that's using Ford readers and there were a few versions of those, lol.
And there were 2 digit code OBD1 and then 3 digit OBD1 until the 4 digit OBD2 standard came along


Yes, EEC power relay closes with key on and powers up the EEC(computer)
And yes it also powers other things at the same time:
Fuel pump relay
Fuel injectors
IAC Valve
EVAP system
And if so equipped:
Automatic trans solenoids
EGR solenoid

So EEC relay issue would be a no start, no run issue

 

2.9l

 

On 1986/88 2.9l code 16 would be Electronic ignition - IDM circuit fault

IDM(ignition diagnostic monitor) is the tach(RPM) signal from the TFI module to the computer, and tachometer if so equipped
Could have been set at any time
It would tend to cause wandering idle but not rough running usually, it could if there was no IDM signal at startup

Did they Clear the codes?

If so check it again in a day or two to see if its back

 

Is it possible there could be something wrong with the distributor itself. Tfi is new. Distributor about 2 years old. It goes from rough to smooth just like that after a few minutes so to me it seems like something is getting signal or is no longer needed for signal at that point. Seems unlikely to me to be distributor.

 

You are correct, mechanical distributor issue would be unlikely if rough running goes away

It reads like the change from Open Loop to Closed Loop is when engine runs better

Does it take longer to run better from cold start than from warm start?

 

Typically it is longer from cold start. But from warm start it’s just as Bad sometimes. Sometimes a little less pens on how long it sat. There’s a huge difference between sitting for one minute and three minutes. When it’s warm if I drive right away it does seem to go away a little quicker but still takes a couple minutes. And then back to perfect driving. I agree it seems like something that’s opening or closing too soon or too late not sure. It seems to me the coolant temperature sensor should be not an issue when warm. That was my very first idea was wrong. When it’s cold And even a little when it’s warm there is a lot of gas smell and some steam or whitish smoke a little bit During the returning to normal process. Clanking and small backfires through the air cleaner if you hit gas. I am stumped.

 

Open Loop is the software in the computer that runs when the computer is first powered up
And computer runs Open Loop software until other parameters are reached
So think of Open Loop as Windows XP

Windows XP has a 2 min timer that it starts when it boots up
When that timer expires it looks at ECT sensor to see if engine is above 150degF
If not then XP continues to run
If above 150degF then XP stops and Windows 8 starts up(Closed Loop software)

If XP is still running then it monitors ECT sensor until its above 150degF, when it is XP stops and Windows 8 starts up(Closed Loop software)

All engine computers have 2 different software systems inside, Open Loop for bootup and Closed Loop when engine is warmed up
But all start in Open Loop, cold or warm doesn't matter
When engine is warm there is a faster switch to Closed Loop Software, that's the only difference

 

OK then it seems to me that if it starts in open loop whether it’s cold or warm then wanted to do in this warm something isn’t telling it to close. But if it’s doing this one it’s cold yet it’s an open loop like it’s supposed to be then there’s Gotta be a bad component or a short in the wire Or something like that. Otherwise it should run just as smooth as it used to when it’s first started up. But being warm and doing the same symptoms that seems to me it’s almost like an open loop way too long like the engine needs of the specifics he would need when it’s cold. I don’t know I am confused for sure. This may be one of the only ones I have never figured out and taken this long

 

And like I was saying before when it’s doing this there’s a strong gas smell and a lot of engine noise although not super loud. Either means too much gas or on burn gas from some kind a weird ignition problem possibly. But so weird from bad to good just like that at a certain point

 

Besides the computer the ignition module and the distributor and coil. Is there anything else the relay a fuse Or anything that would cause any sort of ignition problem.. And with the symptoms that I’m describing I’m just curious what do you think would be the most obvious thing that you probably would’ve thought of when it started. To me I thought for sure it was going to be the coolant temp sensor

 

It does not go into Closed Loop that fast, couple of minutes needed for O2 sensors to heat up

Yes, ECT sensor would be the first thing I would guess as well

Can you test the ECT voltage?
One wire should be 5volt key on
The other 2.5-3volt cold
Under 1volt warm

Thats while its hooked up

Use a sewing needle to pierce wire to test it

 

I will give that a try. I do appreciate your help by the way.not sure how this will all go

 

Yes it is an oddball issue if what you have already done didn't solve it

I had an idea, its a little off the wall, but FREE
Unplug the O2 sensor

That should keep computer in Open Loop all the time

If it does the same thing, i.e. starts to run better after a few minutes then we will know something else, not sure what but something, lol.

 

So it’s interesting the coolant temperature sensor operates as it should. It’s exactly the values you said cold. And as the engine warms up top rain temperatures the one wire does the below one. So that is in good working order. Which makes it even harder now to figure out exactly what’s going on. The engine started to smooth out around 1.7on the one wire. So I won’t be able to do the oxygen sensor till maybe tomorrow. I have a new map sensor and a new intake air temperature sensor. So now at this point I don’t have any idea what is not working right. And like I said the computer is new also basically all the parts I changed made no difference from the old ones. And less by coincidence one of the new parts is a bad one. Again though what makes it so weird is it it does it when the truck is warm after shutting it off and turn it back on. If I turn it off for less than a minute and turn it back on when it’s warm it will run but if it’s any more than that it starts over with All the crap. At least I know the coolant temperature sensor is good

 

Good test

MAP sensor "tests" the air pressure with Key on, the barometric pressure, that gives it a reference point for the Vacuum pressure in the intake manifold after startup
MAP sensor systems didn't do well in Mountains, lol
If you drove from sea level up to say 4,000ft elevation the engine would be running poorly the higher you went, but if you stopped, turned off the key and then turned it back on, the MAP would get the new lower air pressure reference point and engine would run better again..............until you drove back down the mountain, lol, then you stop again to reset MAP
This is just an FYI

MAF sensor systems calculate barometric pressure on the fly so did much better with changes in elevation

The over 1 minute off made me think of O2 sensor again

If computer is NOT starting up in Open Loop as it was designed to, but in Closed Loop, then it would be using a COLD O2 sensor to calculate air/fuel mix, so way off the mark mix and poor running
When when hot the O2 cools off pretty fast when Heater power is cut(key off), so in over a minute it would drop below 650degF so would cause poor ruuning until heater and exhaust got it hot again

This is not an O2 sensor issue, its a computer issue
If you unplug the O2 sensor it should set a code, no heater power, and cause it to stay in Open Loop, or change it to Open Loop

O2 sensors have 4 wires, 2 are for the internal heater, 12v and ground, other 2 are for the sensor part

 

Hey Ron do you think there could possibly be a short in my oxygen sensor. Because it’s interesting after it warms up which activates the oxygen sensor and it’s running great if I turn it off or any more than a minute it runs like crap again until it Switches over and some sensor I don’t know

 

No, that would mean O2 sensor is OK once warmed up, but it could mean computer is using O2 sensor when its cold causing poor running until its warm
Unplug O2 sensor and see how it runs and if it gets better after a few minutes