Ford 2.9 running rough on cold start

drewman26 · Oct 13, 2018

It's been awhile since I had posted anything so here goes.
I've been having cold start problems intermittently. when I start it up it will rev up to 1500 RPM for a second or to then it drops down to 500 then back up to 1500 and it will do that till it settles in at 1300. Then after about 30 seconds later the RPM will drop real low and it starts sputtering and missing real bad almost dying but the rpm will shoot back up to 1300 or 1500. some mornings it will crank up fine and not do it but the problem of it sputtering and missing will still happen. unrelated to this but anytime I go and crank it up warm I have to wait for about 30 seconds for it to lope or it will bog down or jump in the road. I have some throttle problems as well. If I press the gas real lightly like taking off in first gear it will sometimes buck and jump spilling my coffee and will not stop till I take my foot off the gas. codes I had today

KOEO CM 18 I replaced the TFI) (KOER code 41 the O2 is new and hasn't fixed the problem). I have checked for vacuum leaks with ether several times and found none.

List of parts changed:
TFI

PIP

TPS

IAC

IAT

ECT

3 ECM's

O2 sensor

FPR

In-tank fuel pump

in-line fuel pump

both fuel filters

air filter

I apologize if my grammar isn't perfect as I'm running on little to no sleep. The hurricane did a number on GA and have been trying to clean up. Any help is much appreciated!

Thanks

Paulos · Oct 14, 2018

I don't see a MAP sensor in your list, and this is something I would suspect. I had a similar situation with my '87 and an intermittent code 41, and changing the MAP sensor remedied that. I'd do a wiggle test on the TFI connector regarding the code 18.

Also, I installed a new "quality" TFI in my '87 one day after work. It ran fine - until the trip to work the following morning. Apparently the new TFI had slightly thinner pins than the old TFI, and the 31 year old TFI connector didn't like it. Halfway to work the engine quit. It would restart after a minute or two, then die again. A wiggle test of the connector confirmed it was the connector (it immediately died when I wiggled it), and after removing the red plastic retainer in the connector I tweaked the terminals with a very small screwdriver to make them tighter. It got me to work, the auto parts store, and home again. I haven't had it happen again since installing a new connector.

Poor compression in one or more cylinders, or sticking or poorly adjusted valves, can also affect the O2 sensor, causing it to read "lean". I'd do a compression test and a vacuum test. Check out this article I found a while back regarding similar issues troubleshooting 2.9's. It describes some of the symptoms your 2.9 has.

http://www.underhoodservice.com/diagnostic-dilemmas-symptom-diagnosis-the-journey-begins/

drewman26 · Oct 14, 2018

Tanks for your reply! I forgot to mention that I changed out the MAP twice. The TFI is also a motorcraft part. I do not know if this has anything to do with it but the engine harness where it connects right at the driver fender looks like crap so I used some liquid electrical tape to cover the bare wires. It was like that when I got it. I assume that the old owner was trying to fix the AC harness and did this. Here are some pictures.

Thanks

RonD · Oct 14, 2018

Fuel injected gasoline engines still needs to be Choked on cold start
Choke means Rich Fuel Mix and High Idle

The computer does this since there are no Jets, so choke plate wouldn't work
With key on, computer opens IAC Valve all the way, always.

Computer gets engine/coolant temp from the ECT sensor, if cold it knows to add extra fuel and to set IAC Valve for above 1,000RPM idle once engine is started, above 400rpms.

When you start any fuel injected engine, warm or cold, engine should REV, because IAC Valve is open all the way, 1,500rpm REV is not unreasonable

If engine is cold RPMs should drop to 1,100 or so after this REV, and then slowly drop to about 650rpms(manual trans) over the next 5-8 minutes until engine is warmed up

Yours is stumbling but why?
You could have a drop in fuel pressure just after startup, computer doesn't start fuel pump full time until RPMs are above 400
Try cycling key on and off a few times BEFORE starting cold, that builds up any lost fuel pressure.
See if stumbling goes away, cold start needs more fuel than warm restart

Could be IAC Valve or computer wiring issue, but would expect stumbling when warmed up as well, should just be when cold, but could happen, temp sensitive wire connection.

ECT sensor wiring issue
ECT sensor uses 5volts from computer, it returns 2.5-3volts when cold, then under 1volt when warm, .5-.7v
Its possible that bad connector is causing voltage to change, drop low, so computer exits Choke Mode, IAC Valve closes for lower idle, which on a cold engine would be very low, then computer tries to recover RPMs by opening IAC Valve more so surge in RPMs, then it starts to move IAC valve to set RPMs at current ECT Temp voltage.

Its possible its spark related, but not TFI module, check SPOUT connector and wire

Paulos · Oct 14, 2018

Actually, it's common for the insulation on the wires in those connectors to apparently shrink, almost like they got hot. Mine were similar before I cut out the connectors and soldered and heat-shrinked the joints, but they weren't quite as bad as yours. I believe I read somewhere on this forum that someone had intermittent problems with his 2.9 cutting out and repairing the wires at these connectors solved his problem. It didn't help me, but now I know these connectors are not an issue

. I'm an electrician and I wouldn't trust that liquid tape as far as I could throw it.

drewman26 · Oct 14, 2018

Thanks for the replies guys. the fuel pressure could be dropping down low or the ect wiring could causing the problem. I will check the wiring when I have some more time and I'll try cycling the key and see if that helps. Going back to compression, when I got the truck I had that checked to make sure it was worth fixing and all 6 came back pretty good. I also found a video of someone having the same problem with a 2.9 and it happened to be the MAP sensor went bad. It could be that the one I bought went bad. I should have stated that I changed out the factory ford MAP with a junk yard one, then bought a new one about a year ago and that at the time made it run better but it still had the loping problem that would happen on hot starts.

Question is could I use the MAP sensor off my 95 150 for testing? I think they both have the same part number. My thought is that the fusible link for the O2 heater or the map might be causing my lean code.

Thanks again,

Drew

RonD · Oct 14, 2018

MAP sensor uses a vacuum line from the intake to detect engine load, so make sure the vacuum line is not cracked or damaged

MAP sensors can fail just not all that common, they are pretty simple devices and have no "moving parts" to wear out
Usually its moisture getting inside that "kills" them, same thing happens to DPFE sensors, which are also pressure sensors

But yes, since the MAP tells computer engine load computer uses that info to set air:fuel mix for that moment in time
After mix is burned in the engine O2 sensor tells computer if air:fuel mix was correct, correct amount of Oxygen in the exhaust.
If there was too much oxygen then computer adds more fuel, until O2 reports correct Oxygen levels in exhaust.
If computer has to add too much extra fuel then it will set a Lean Code, engine was never running Lean, well for maybe 1 second, lol.
The Lean, or Rich, codes are to let the driver know that computer calculations are off, usually off by 20+% to set the code.
This can be from air leaks, sensor issue, fuel issue, computer issue.

You can even get a False Lean if there is an exhaust leak between head and O2 sensor, exhaust leaks SUCK IN air, so O2 sees too much air/oxygen.
MPG will go down with this, because engine is actually running Richer than it should

drewman26 · Oct 14, 2018

Good News!

I think I have it fixed. Thanks Paulos & RonD for putting that thought in my head! I switched the MAP sensors out. My truck fired up and held cold idle perfect and didn't surge at all. I guess the MAP failed like you said.

The only problem I'm still having is the idle surge 30 seconds after a hot startup. I will try to best describe the problem, so here goes: after I crank it up, it will rev to 1300 then settle back to 850, then after 30 or so seconds I can hear the engine start throttling up(opening the IAC) and the tach starts fluttering between 1100 and 750, then it shoots up to 1100 and settles back at 850-900. My thought is its going from open loop to closed loop. If I take off without waiting for it to do that the truck has no power and hesitates, then all of a sudden it picks up power and goes. If it is switching into closed loop I shouldn't feel the switch, should I?

Thanks,

Drew

Ford 2.9 running rough on cold start

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