Fuel issues

[1986RangerXL]

The truck is a 1986 Ranger w/ 2.9, which has sat since 2010. The truck will idle okay for a few seconds, then the motor falls off a cliff for a couple seconds before returning to idle. We replaced the thermostat and now the truck does the same thing until it's been ran for around 10min, then it will drive normally. I took it to get gas after running it for 10min and it ran fine, but after stopping for about 15min it started bucking again on the way back (1st and 2nd gear were horrible, third a bit more manageable). Completely stumped on this one.

We replaced the fuel lines, both fuel pumps, distributor (properly timed it), spark plugs, and the plug wires prior to this issue. As well as the solenoid and positive battery cable.

Was going to try fuel injector cleaner (Seafoam) before the radiator busted, now waiting for the radiator to come in. Going to get pressure readings on the pumps as well

Any ideas what causes this? Thanks

 

[Dirtman]

Pressure check the fuel system, vacuum test for an exhaust restriction, check the ECT sensor.

 

[1986RangerXL]

Pressure check the fuel system, vacuum test for an exhaust restriction, check the ECT sensor.

Thanks, first time ever wrenching, where is the ECT sensor?

 

[Dirtman]

That you would have to ask one of the 2.9 guys. @PetroleumJunkie412

It's usually on the intake manifold somewhere. 2 wire sensor (engine coolant temperature) sensor. This is not the same sensor that runs your temp gauge on the instrument cluster. The ECT sensor is only used to tell the computer if the engine is cold or hot and adjust the fuel mix accordingly. If it goes bad it can cause the engine to run like crap when cold but fine when it warms up or vice versa.

 

[RonD]

On the 2.9l there are two temp devices
ECT(engine coolant temp) sensor, it uses 5volts, 2 wires and is only connected to the computer

ETC sender, it uses 12volts, 1 wire(on 2.9l), and is only used by dash board temp gauge

Both are located near each other on the lower intake near thermostat housing, so at the top front of lower intake

As shown above they are NOT interchangeable, lol


The computer needs the ECT sensor to choke the engine when its cold and then to set idle according to temp readings
Higher idle cold then slow drop in idle until fully warmed up
From the 5volts, the ECT sensor sends back about 3volts cold and under 1volt fully warmed up, so voltage goes down as engine warms up

The computer uses the IAC Valve on the upper intake to set the idle RPMs, based in ECT temp, these can be cleaned, not hard to do
After sitting a long time it could be sticking


Yes, after sitting that long the Seafoam should help clean fuel rail and injectors

There are 2 fuel lines that come up into the engine bay
The IN from pumps and filter runs to the fuel rail
The OUT/return line runs from the FPR(fuel pressure regulator) back to the gas tank

The FPR will have a vacuum hose attached, pull it off and check it for gasoline, FPR can leak and cause running issues from extra gas being sucked in thru that vacuum hose, replace FPR is gasoline is in that vacuum hose

When you are testing fuel pressure, with engine running, 30-35psi is expected, unhook that vacuum hose and you should see 40-43psi, then plug it back in

 

[PetroleumJunkie412]

RonD got it. Thanks, God of Canada!

 

[Josh B]

The computer uses the IAC Valve on the upper intake to set the idle RPMs, based in ECT temp, these can be cleaned, not hard to do
After sitting a long time it could be sticking


Yes, after sitting that long the Seafoam should help clean fuel rail and injectors

Is that Seafoam in the tank, or in the intake? I saw someone describe the "into the intake method" somewhere but can't find it, wish I knew now how it went :/

 

[PetroleumJunkie412]

Both. Use in crankcase, or feed into vac line

 

[Dirtman]

Just buy the damn spray bottle if you want to do the intake, hook the nozzle to the intake tube and spray until the can is empty. Never understood why you would buy the regular pour can if your running it through the intake. They even sell it in a 2 pack, one to pour in the gas tank, one to spray in the intake... it's like wiping before you poop, it just doesn't make sense!

 

[RonD]

In the gas tank it cleans the fuel system

In the oil it cleans out sludge

In the intake it cleans out carbon build up

 

[Josh B]

In the gas tank it cleans the fuel system

In the oil it cleans out sludge

In the intake it cleans out carbon build up

How much do you put in the oil, and how long do you leave it in there?

 

[Shran]

I would add no more than half a can to the oil and I would not leave it in there real long. Right before an oil change preferably. The more you add, the thinner the oil becomes. Diesel fuel/kerosene added to the oil does basically the same thing and quite a bit cheaper.

In the fuel, it's almost pointless unless you're close to empty - a can diluted into 17+ gallons will do nothing. I dumped two cans of off brand "stay tuned" additive (same thing as seafoam) into about 3 gallons of gas and let it idle for quite a while... it seemed to help quite a bit. Truck had sat for quite a few years and had issues with surging idle and lack of throttle response, totally cleared up.

Not sure if it makes a difference in the intake or not. I've run nasty, carboned up intake manifolds through the parts washer and it takes a lot of scrubbing and solvents to clean them up. I don't think I'd even bother... that tiny little bit of solvent sucked through as the engine is running won't do much.

ECT sensor may help, clean out the idle air control valve.

 

[Dirtman]

I agree 1 can in the tank is more for maintenance than real cleaning. I do a can in the tank every couple months. Does it make a difference added to the fuel in small doses? Who knows. I wouldn't use it in the crankcase because their are better products for that.

The intake spray does work though. People have decarboned engines with water for decades. It's the steam and added pressure that does the work. Seafoam works the same way. Ford actually has a TSB about how to decarbon engines and they use a similar product called PM-3 just sprayed down the intake tube or sucked through the brake booster line.

 

[RonD]

Just as a HEADS UP!!!

Putting any liquid into the intake of a running engine can cause a Hydro-Lock which WILL(not may) bend a connecting rod or break a piston
Spay fluid in, do not pour liquid in because an "oops" can cost you ALOT of $$$

 

[Dirtman]

Now now... don't scare the children!