2.9 only starts in "clear flooded engine mode"

[1988xltsupercabranger]

Greetings fellow 2.9 owners,
I bought this truck with a cracked head that ran excellent with zero issues and have installed 2 new aftermarket heads. Now it doesn't want to start unless I floor the accelerator and once it's running, its pretty rough/misfiring. I've replaced the MAP, IAC, O2, intake temp, coolant temp, TPS sensors, and purchased rebuilt injectors; timing is set 12deg btdc, new plugs/wires, fuel pressure is 40 and no fuel in vacuum line at FPR. Any suggestions on where to look next? Thinking I'll test every component of the ignition system next but I have a feeling there's a computer/wiring issue.

Any help is appreciated
Sam

 

[1988xltsupercabranger]

@RonD I'm looking forward to your opinion

 

[RonD]

not sure why, I think its broken.......................but don't quote me on that

With all the stuff that's been changed it makes it harder to diagnose
"new" stuff now a days has a 15-20% chance of being bad out of the box
So if you change 5 things you will be close to or at 100% chance of one of the parts being bad, lol


In any case try 50/50 test but unplug the fuel pump relay first, its the relay with the green base
Then crank the engine over a few times so no pressure or fuel at the injectors
Reads like engine is flooding out, so it may even start and sound better as fuel runs out

Take the air filter hose off the intake and spray some gasoline or ether in it and try to start engine, don't touch gas pedal
If it starts up OK, runs then dies Spark is OK
If you have a helper to start engine see if you can keep it running, at idle, by spraying fuel into intake
That would confirm Spark timing and firing order is OK

If engine won't start or runs like crap then spark is at least some of the problem
Firing order is a big thing, I goof that up all the time and would bet money its correct, after the 3rd time checking it I am satisfied its perfect..............and I am wrong, lol


If it is flooding out then you will need to open up the computer and have a look at the circuit board, there are 2 or 3 barrel capacitors that will leak after 20+ years and cause issues, under $5 to repair

 

[1988xltsupercabranger]

not sure why, I think its broken.......................but don't quote me on that

With all the stuff that's been changed it makes it harder to diagnose
"new" stuff now a days has a 15-20% chance of being bad out of the box
So if you change 5 things you will be close to or at 100% chance of one of the parts being bad, lol


In any case try 50/50 test but unplug the fuel pump relay first, its the relay with the green base
Then crank the engine over a few times so no pressure or fuel at the injectors
Reads like engine is flooding out, so it may even start and sound better as fuel runs out

Take the air filter hose off the intake and spray some gasoline or ether in it and try to start engine, don't touch gas pedal
If it starts up OK, runs then dies Spark is OK
If you have a helper to start engine see if you can keep it running, at idle, by spraying fuel into intake
That would confirm Spark timing and firing order is OK

If engine won't start or runs like crap then spark is at least some of the problem
Firing order is a big thing, I goof that up all the time and would bet money its correct, after the 3rd time checking it I am satisfied its perfect..............and I am wrong, lol


If its is flooding out then you will need to open up the computer and have a look at the circuit board, there are 2 or 3 barrel capacitors that will leak after 20+ years and cause issues, under $5 to repair

I agree it's broken LoL Much appreciated, I'll try the 50/50 test. I kept it running long enough to use a timing light although it was at 2.5 or 3k rpm and spout was removed. I just realized maybe timing is off because I didn't time it at Idle . I'll report back after the 50/50

 

[1988xltsupercabranger]

I couldn't get it to stay running with the 50/50 test although it does start and run if intake hose and TPS is removed. It idles at 3k rpms with intake hose removed. Sounds like it's flooded out, is the computer board with bad capacitors on the passenger side wall behind the trim?

 

[1988xltsupercabranger]

I couldn't get it to stay running with the 50/50 test although it does start and run if intake hose and TPS is removed. It idles at 3k rpms with intake hose removed. Sounds like it's flooded out, is the computer board with bad capacitors on the passenger side wall behind the trim?

@RonD

 

[RonD]

Yes, computer is in the cab behind passenger side kick panel
Unhook one battery cable before unplugging computers 60-wire connector

Did you unplug the fuel pump relay for the test?

 

[1988xltsupercabranger]

Yes, computer is in the cab behind passenger side kick panel
Unhook one battery cable before unplugging computers 60-wire connector

Did you unplug the fuel pump relay for the test?

Yes, fuel relay was unplugged for 50/50 test, I plugged it back in and left the TPS unplugged and intake hose off and tried to start it out of exasperation and that's when it started right up and idles at 3k. Found this capacitor kit that looks like the correct repair unless you have the specs on what capacitors it needs. https://www.amazon.com/1987-1996-Ford-ECU-Capacitor-Repair/dp/B076R36TPG?tag=959media-20

 

[1988xltsupercabranger]

I can't see any leaking capacitors, do the capacitors go bad without anything visual wrong?

 

[RonD]

Move each a little with finger to see if one of the wire has corroded

But usually it will be obvious if its leaking or corroded

I don't see anything obviously wrong

Does the 60-pin connection also look as clean?


With fuel pump relay unplugged the engine can't flood out, so I am a little perplexed by that
It should have started and idled by adding fuel manually if "flooding" was the only issue

Since the gasoline engine was first invented it would run fine by manually adding fuel, called it a carburetor, lol

 

[1988xltsupercabranger]

Move each a little with finger to see if one of the wire has corroded

But usually it will be obvious if its leaking or corroded

I don't see anything obviously wrong

Does the 60-pin connection also look as clean?


With fuel pump relay unplugged the engine can't flood out, so I am a little perplexed by that
It should have started and idled by adding fuel manually if "flooding" was the only issue

The 60 pin connector is clean, both leads look clean on the capacitor. I only see one capacitor.

I was using ether to start it, maybe I should try fuel. Would my timing it at 3k rpm make the timing off?.spout was out as well. It runs really smooth at 3k rpm without the intake hose.

 

[1988xltsupercabranger]

Move each a little with finger to see if one of the wire has corroded

But usually it will be obvious if its leaking or corroded

I don't see anything obviously wrong

Does the 60-pin connection also look as clean?


With fuel pump relay unplugged the engine can't flood out, so I am a little perplexed by that
It should have started and idled by adding fuel manually if "flooding" was the only issue

Since the gasoline engine was first invented it would run fine by manually adding fuel, called it a carburetor, lol

I just pulled the fuel relay again and it idles with fuel sprayed into the intake. I was being stingy with the ether

 

[RonD]

The intake hose on the 1988 2.9l has no other function than as a connection to air cleaner box, this year doesn't use a MAF sensor, it has a MAP sensor connected to intake manifold directly via vacuum hose

So having the intakes hose/tube off shouldn't matter at all unless air cleaner or boxes opening is clogged up

Thats good that it runs at idle RPMs by manually adding fuel

NO, you should not set base spark timing at 3,000rpms
Need to be under 1,000rpm, as close to 750rpm as practical, so after engine is warmed up and idling

Spark timing changes with RPMs because the time it takes a piston to go from say 15deg Before TDC to 15deg After TDC changes with RPMs
The time it takes a 14.7:1 air:fuel ratio to fully ignite with a spark is say 200ms(milliseconds), its not instant
You want FULL explosive power to occur AFTER piston is just passed Top Dead Center, so it can push down on the crank to add power, 5 to 10deg After TDC, so it has some leverage to push down on crank

So you time the spark to start ignition Before TDC so full ignition occurs After TDC
If piston at 750rpms travel 20degs in 200ms then timing spark at 10deg BTDC would have full ignition at 10deg ATDC
If you set it at 12deg BTDC the full ignition would happen at 8deg ATDC

The TFI module has an RPM advance that automatically moves the spark timing up to 30+deg BTDC at maximum RPM because piston speed is much faster, but the air:fuel mix still takes that 200ms to fully ignite
So the 10-12deg BTDC recommendation only applies to RPM under 1,000

Just FYI on the SPOUT and what its for
One monkey in the wrench on spark timing is fuel mix ratios, richer fuel mix burns faster, than the 200ms 14.7:1 ratio
RPM advance is fine, UNTIL air:fuel mix changes
So spark advance needs to change timing based on fuel mix ratio also, called engine Load advance, thats what the SPOUT is for, the computer "knows" the fuel mix it is using so "tells" the TFI module what to do via the SPOUT wire
On older distributors this was done with Vacuum Advance on the distributor, intake manifold vacuum levels change with LOAD on the engine

So to set base spark timing you need the engine warmed up and idling under 1,000rpm and the SPOUT(or vacuum advance) needs to be disabled

The 200ms and piston degrees traveled speed is all made up numbers, just as examples of how it works
Actual numbers are out there if you want that info


Engine is obviously running Rich so either fuel pressure is way too high, pump is capable of 80+psi, but computer expects 35psi
Or injectors are leaking, more than one which is a long shot
Or FPR is leaking fuel thru vacuum hose
Or computer has lost its mind as far as fuel ratios, computer is last on the list for a reason, it is rarely the problem, not never just rarely

1988 2.9l computer uses Batch fire fuel injection
Fuel injectors are controlled(opened) by the computer grounding them, all injectors get 12volts with Key On
Sequential fuel injection has 1 ground wire back to the computer for each injector, so 6 wires in a V6

Batch fire for V6 just has 2 ground wires back to the computer, 3 injectors are opened every 1 RPM, other 3 are opened on the next RPM, so they alternate
2 injector on one bank and 1 injector on the other bank, usually Odd and Even
So injectors 1, 3 and 5 open, then next RPM 2, 4 and 6 open
If one of these 2 ground wires was "shorting" to vehicle ground, then injectors would open with key on, flooding out the engine
With key on engine off no injector should show a ground on its "NOT RED" wire, red wire is the 12v

 

[1988xltsupercabranger]

The intake hose on the 1988 2.9l has no other function than as a connection to air cleaner box, this year doesn't use a MAF sensor, it has a MAP sensor connected to intake manifold directly via vacuum hose

So having the intakes hose/tube off shouldn't matter at all unless air cleaner or boxes opening is clogged up

Thats good that it runs at idle RPMs by manually adding fuel

NO, you should not set base spark timing at 3,000rpms
Need to be under 1,000rpm, as close to 750rpm as practical, so after engine is warmed up and idling

Spark timing changes with RPMs because the time it takes a piston to go from say 15deg Before TDC to 15deg After TDC changes with RPMs
The time it takes a 14.7:1 air:fuel ratio to fully ignite with a spark is say 200ms(milliseconds), its not instant
You want FULL explosive power to occur AFTER piston is just passed Top Dead Center, so it can push down on the crank to add power, 5 to 10deg After TDC, so it has some leverage to push down on crank

So you time the spark to start ignition Before TDC so full ignition occurs After TDC
If piston at 750rpms travel 20degs in 200ms then timing spark at 10deg BTDC would have full ignition at 10deg ATDC
If you set it at 12deg BTDC the full ignition would happen at 8deg ATDC

The TFI module has an RPM advance that automatically moves the spark timing up to 30+deg BTDC at maximum RPM because piston speed is much faster, but the air:fuel mix still takes that 200ms to fully ignite
So the 10-12deg BTDC recommendation only applies to RPM under 1,000

Just FYI on the SPOUT and what its for
One monkey in the wrench on spark timing is fuel mix ratios, richer fuel mix burns faster, than the 200ms 14.7:1 ratio
RPM advance is fine, UNTIL air:fuel mix changes
So spark advance needs to change timing based on fuel mix ratio also, called engine Load advance, thats what the SPOUT is for, the computer "knows" the fuel mix it is using so "tells" the TFI module what to do via the SPOUT wire
On older distributors this was done with Vacuum Advance on the distributor, intake manifold vacuum levels change with LOAD on the engine

So to set base spark timing you need the engine warmed up and idling under 1,000rpm and the SPOUT(or vacuum advance) needs to be disabled

The 200ms and piston degrees traveled speed is all made up numbers, just as examples of how it works
Actual numbers are out there if you want that info


Engine is obviously running Rich so either fuel pressure is way too high, pump is capable of 80+psi, but computer expects 35psi
Or injectors are leaking, more than one which is a long shot
Or FPR is leaking fuel thru vacuum hose
Or computer has lost its mind as far as fuel ratios, computer is last on the list for a reason, it is rarely the problem, not never just rarely

1988 2.9l computer uses Batch fire fuel injection
Fuel injectors are controlled(opened) by the computer grounding them, all injectors get 12volts with Key On
Sequential fuel injection has 1 ground wire back to the computer for each injector, so 6 wires in a V6

Batch fire for V6 just has 2 ground wires back to the computer, 3 injectors are opened every 1 RPM, other 3 are opened on the next RPM, so they alternate
2 injector on one bank and 1 injector on the other bank, usually Odd and Even
So injectors 1, 3 and 5 open, then next RPM 2, 4 and 6 open
If one of these 2 ground wires was "shorting" to vehicle ground, then injectors would open with key on, flooding out the engine
With key on engine off no injector should show a ground on its "NOT RED" wire, red wire is the 12v

Bingo, both banks are shorted out

 

[RonD]

Pins 58 and 59 on the computer connector are the two injector ground wires
Usually a tan/red wire and green/white wire, can be tan and white

With computer connector off and battery hooked back up, and key on, each of those wires should show 12volts
If not then they are indeed grounded in the wiring harness

If you see the 12volts then the ground is IN the computer

Key on 12v------(red wire)--------------injector----------(tan/red wire)----------------pin 59(computer)

Electrically an injector is just a coil of wire, so 12v in = 12v out
And Ford uses 14ohm injectors so very little voltage drop