Rebuilt motor running rich

[PacoTaco1000]

This winter my father and I rebuilt my 2.9l for my ‘88 that I bought in October. We finally have everything in place and have it broken in but, It’s running rich at idle, and when you create a vacuum leak it starts to level out but only when warm.

So far we’ve got a new MAP sensor, temp sensor, Oil pressure sensor, oil level sensor, air filter, in tank fuel pump, both fuel filters, new injectors, timing set, and the whole bottom end is new.

We made sure timing marks lined up still before putting the front cover on. The TPS checked out at the level it was supposed to be, and the old map sensor was stuck at a constant level. It took a while to get it started up initially and we had a few problems along the way but no idea what could be the cause. This is my first motor build and my first truck.

Anyone have any ideas?

 

[RonD]

Welcome to TRS

On the engine there will be two Fuel lines, one is from the fuel pump the other is the Return fuel line
The Return fuel line is connected to the FPR(fuel pressure regulator), it looks like a small "can"
The FPR will also have a Vacuum hose connected, remove this hose and check it for fuel, replace FPR if fuel is found, this is why its running Rich, extra fuel is being sucked in

If possible check fuel pressure, 30-35psi is expected, if higher then thats the problem
Return line can get plugged(rare) or FPR is not opening which causes pressure above 70psi

Have you checked if there are any "codes" in computer memory, you can do that with a 12volt test light

The computer runs the injectors so sets the Lean/Rich fuel mix
It has 2 modes of operation
When engine is cold, coolant temp lower than 140degF, it runs Open Loop, this is a Choke Mode and computer uses tables in memory to "guesstimate" air/fuel mix based on RPM and engine load(MAP sensor)
Computer is programed for injector size and fuel pressure, so if pressure is higher that 40psi then more fuel would come out of each injector, causing rich running

It has to run Open Loop because O2 sensors can't work until they are heated above 650degF
When O2 sensors are hot enough and coolant is above 140degF then computer changes to Closed Loop
Closed loop means it has FEEDBACK on whether or not the air/fuel mix is lean or rich based on O2 sensor voltage
O2 sensors see only Oxygen, too much oxygen in exhaust means Lean burn, to little oxygen a rich burn

So there are two modes of operation, engine cold, engine warmed up
This can help determine where a fault might be
Engine runs fine cold, then stumbles when warm
Engine stumbles cold but runs better when warm

And not a bad idea to open up computer case and look at the circuit board inside, there are 2 or 3 capacitors on the board that can leak and cause fuel mix issues, there can also be water damage, free to have a look

 

[PacoTaco1000]

Thank you for the input! Here’s just some more general info in case more things help narrow it down while i test your suggestions.

I took it to a mechanic who lives down the road from me to check things out and he tested the TPS, checked fuel pressure, and compression in the cylinders, he started to get busy with projects so i just got it back today and am out of ideas myself.

i will definitely check for fuel in the FPR though then. I was thinking there might be a chance of the injectors being for the wrong application? We had to bore the cylinders 30 over, and i got the FJ717 injectors off of Rock auto.

We haven’t been quite able to check codes yet. The mechanic was more equipped for newer cars with more readings, i’ll have to try that and get back to you.

When it initially starts up, it’s immediately too rich, when it finally warms up it’s still rich and runs rough but when you take a vacuum hose out it starts to sound better but not quite there. I’ll try to conduct some of the test though and check back in to see if we can’t figure this out. Thank you again! This site’s been a huge help before i made this account and i’m looking forward to using it more, we’ve got two of these 2.9’s that my dad and i are rebuilding so it’s been an interesting journey

 

[RonD]

FJ717 injectors should be OK, couldn't find the specs on it, should be around 16lb/hour for the 1988 computer

Did the mechanic know that Rangers used 30psi fuel pressure, until 1997 and then switch to 65psi??
Because if he was "used to newer cars" he may have thought over 50psi was OK

Taking off vacuum line on a MAP system engine does two things, adds more air but also changes MAP frequency back to computer

Good site here to read up on how the older Speed Density system works: http://www.fuelinjectedford.com/
You can see what each sensors purpose is for
TPS might not be what you think its for

After warm up the Computer should see the O2 sensor showing low oxygen(rich), then it should self correct for the rich mix
O2 sensors have a mile and time limit, 100k miles or 12 years, which ever comes first
And as they wear out(run out of chemicals) they tell computer exhaust is leaner and leaner, and its a FALSE lean, so computer runs engine richer than it should
If you haven't change the O2 and don't have a history of when it was last changed, I would change it just on speculation, or as general maintenance

And computer's "remember", they have a long term fuel trim they store in memory, so when started cold they use the pre-mix Tables but then add extra fuel because of the "average" fuel trims learned over the last months of driving
You don't have any long term data so it won't have an average it can use, just has the warmed up time from a day or two to use

 

[PacoTaco1000]

When he walked me through the readings, he said between 30-35, his equipment is more for newer but he has 40+ years of experience and has worked on 2.9s before, it’s just been quite a few years. I’ll definitely look into the O2 sensor first, i checked the FPR and it was as dry as the first installation of one would be. The O2 wouldn’t affect the mixture for cold running though would it? I’ll end up changing it either way, just curious

 

[RonD]

No, it shouldn't have caused an issue with cold start if computer had been unplugged from power for longer than a day or two
But I couldn't find the specs of the injectors you installed, hoping the "17" at the end means 17lb/hour flow


The computer uses ECT sensor for cold start to set the amount of Choke to run, the colder it is the more Choke is applied
Choke just means to add extra fuel and run a high idle
Cold gas engines need RICH mix to stay running, thats what a Choke Plate on a Carb did, restricted air flow into carb which increases vacuum, which increases fuel sucked from the Jets

 

[PacoTaco1000]

Since we have had the engine out and battery unplugged from the truck since Christmas, would that affect the computer’s memory?

i got the injectors from Rock auto, i’ll check the specs then and see what they say.

 

[RonD]

No, shouldn't effect operation just would have no memory data saved

 

[PacoTaco1000]

We’re gonna change the O2 sensor and see if that helps

 

[PacoTaco1000]

I also haven’t been able to find specs, i even went to Standard Motor Products’ website and tried to find the model injector and it wouldn’t let me into the page to see details

 

[RonD]

Yes, the injector checks out as being for the 2.9l engine, but thats all I could find

If O2 is more than 12 years old its not a waste of money


There is a test for Leaking injectors, its actually something built into all fuel injection computers
Called "The Clear Flooded Engine routine"

Turn on key
Press gas pedal down to the floor and hold it down all the way
When computer sees 0 RPMs and WOT(wide open throttle) from TPS, it enters Clear flooded engine routine

Computer turns OFF fuel injector pulses but spark stays on

Now crank engine over, it should not fire or start, no fuel
If it fires or starts then you could have leaking injector

If it just cranks then no leaking injectors
Release gas pedal at anytime and injectors will start
I use this every morning on my high mile 4.0l, like to get oil pumped up thru the system before I let it start

If engine does fire or start, check throttle first, press gas pedal to the floor then make sure throttle on engine is indeed open all the way, throttle cables stretch so while pedal is on the floor throttle may not be at WOT, so no Clear flooded engine routine

If that checks out then you can use this same test to find the leaking injector(s)
Unplug coil from cap, no spark
Cycle key on and off 3 times, builds up fuel pressure
Do Clear flooded engine test again
Now pull out spark plugs one at a time and find the ones with WET tips, the leaking injectors are on those cylinders

 

[Paulos]

The injectors you bought are 23lb injectors (one site I checked says 24.5lb). The stock injectors in an '86 and '87 2.9 that I have are 14lb (0 280 150 727). I bought new 15lb Accel injectors a couple years ago and have always felt they were causing my stock 2.9 to run a little rich, but in my case it may be due to the sloppy loose EGR tube that connects to the drivers side exhaust manifold (or a really tired short block).
Here's a couple links I found.

Injector Planet | Genuine OEM Rebuilt Flowmatched fuel injectors

Replace your old clogged fuel injectors with our profesionally rebuilt fuel injectors flow matched for a balanced smooth running engine. we only use best quality cores from OEM brands such as Bosch Delphi Denso Jecs Keihin Lucas Nikki Siemens. beware of cheap chinese fakes / copys your car will...

www.injectorplanet.com

Bosch Fuel Injectors, flow rates & injector connectors

Bosch Fuel Injectors, flow rates. injector connectors. Bosch EV 1, EV 6, EV 12 & EV 14, Bosch hose end & Side feed Fuel Injectors

www.injectorrx.com

I personally don't think that boring the cylinders 0.30 over alone is enough to merit 23lb+ injectors.

 

[PacoTaco1000]

The injectors you bought are 23lb injectors (one site I checked says 24.5lb). The stock injectors in an '86 and '87 2.9 that I have are 14lb (0 280 150 727). I bought new 15lb Accel injectors a couple years ago and have always felt they were causing my stock 2.9 to run a little rich, but in my case it may be due to the sloppy loose EGR tube that connects to the drivers side exhaust manifold (or a really tired short block).
Here's a couple links I found.

Injector Planet | Genuine OEM Rebuilt Flowmatched fuel injectors

Replace your old clogged fuel injectors with our profesionally rebuilt fuel injectors flow matched for a balanced smooth running engine. we only use best quality cores from OEM brands such as Bosch Delphi Denso Jecs Keihin Lucas Nikki Siemens. beware of cheap chinese fakes / copys your car will...

www.injectorplanet.com

Bosch Fuel Injectors, flow rates & injector connectors

Bosch Fuel Injectors, flow rates. injector connectors. Bosch EV 1, EV 6, EV 12 & EV 14, Bosch hose end & Side feed Fuel Injectors

www.injectorrx.com

I personally don't think that boring the cylinders 0.30 over alone is enough to merit 23lb+ injectors.

Where did you find that info? I wouldn’t mind seeing for myself as well just to know, i had a hunch it was Wrong for a while

 

[PacoTaco1000]

Nevermind, i saw the links. Where do you normally get your injectors?

 

[RonD]

That would explain the RICH running for sure if they are indeed over 20lb/hr injectors