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Terrible idle and then dead, tought to keep running "FAST EFI"

I have absolutely no experience with that system, but on a factory system, a fault in the temperature sensor circuit will cause rough/rich idle.

The PCM sees the motor as being cold and dumps in extra fuel...?
 
A1971Blazer said:
I have absolutely no experience with that system, but on a factory system, a fault in the temperature sensor circuit will cause rough/rich idle.

The PCM sees the motor as being cold and dumps in extra fuel...?
Click to expand...
The hand held shows a steady temp so that's not the issue.
 
Stupid question, what's your MAP sensor doing? Looks to me like it's running rich most of the time, indicating fueling is off for some reason...engine assuming it's under more load (low vacuum), bad O2, etc.

What's the fuel pressure look like? FWIW with my low fuel pressure I was getting all sorts of seemingly contradictory info (rich O2 I couldn't affect, stalling, horrible smell, poor/no idle, off-idle stumbling, backfiring, breaing up at specific engine RPM's, pulling plug wires didn't seem to make any difference in idle, etc), fuel presure test would have shown that to me YEARS ago.
 
Yeah, I think low fuel pressure is still one of the main suspects here.
 
Luckily for many of us with an autozone close by, its a free/easy test. Never hurts to confirm things like this.
 
It sounds like he has a fuel pressure gauge. It would be silly to do a fuel injection conversion without having one.
 
My first post has the fuel pressure readings. The regulator has a vacuum line going to it, it looks good, but even if it was broken it wouldn't have more than ~3psi affect. I'm just hoping that when I do find the time to work on it, it winds up being something simple. Thus far, I've only pulled the air cleaner. :( :(

I pop the hood and have my brother take a look at the fuel pump pressure gauge. It should be ~44 psi. It will run 44psi while it's choking at idle. To keep it from dying, I bring it up to ~1200rpm at which point it's controllable, but the fuel pressure is ~34psi. That's weird.
Click to expand...
 
So I finally had a second to look it this. Haven't checked everything yet.

Started truck and ran around to hold throttle linkage open some with my hand.

Checked timing and it was good.
Checked coolant (cause who knows if something blew)
Fuel pressure was ultra steady at 44 psi
Truck will run at 1100 rpm smooth, no hiccups, burps, stumbles, shudders, etc
Once you TRY to bring it down lower, it stumbles really bad to ~550 rpm and lower. Blows rich black smoke like a diesel.
Pull on the throttle just a tad and it clears right up. Snap the throttle FAST and it responds perfect. I can sit there and play vroom vroooom vrooooooooooooooom all day long, with smooth operation, but I can't go below 1100 rpm.

Gotta find some more time to check things out. The FAST guy on the phone told me to check some of these things but I don't think he understood the problem. Seemed like he thought the idle was high or idle screw changed, but it's not an idle "speed" issue, it's an inability to idle. So I'll be calling again tomorrow. Got a high school friend coming through from Dallas area and wouldn't mind doing some wheeling on Sunday. At least I don't have any codes, so I guess all the FAST hardware is good. Hopefully I can get this sorted out.
 
Is this a MAF or speed density system? What you describe sounds a lot like what happens when you get a vacuum leak to let un-metered air into a MAF system. The more air the engine flows, the less effect it has on mixture. Plus a leak is worst at highest vacuum (idle or decel). The fuel is calculated for *measured* air flow, so when you let additional air in it's too lean. The feedback from the O2 can only adjust fuel up as far as the fuel trims allow (don't know what FAST allows).

But blowing smoke means it's rich - so you could have a leak affecting just one bank or something and the O2 feedback is making the other rich.
 
To answer what I can, for now.

It has a MAP reading, so I'm guessing only speed density.
I've seen the O2 sensor freak out around 8:1 while it's dying.
I pulled the vacuum line to the fuel pressure regulator. This gave the system an 1/8" vacuum hose leak. But I didn't notice any changes in behavior.


What gets me is the combination of readings while it's dying. A/F ratio is off the charts rich. At the same time the IAC is WAY high, trying to suck in more air. The "load %" goes from ~30% at idle to ~70% or more. This should be much lower considering WOT should be 100% load on the engine.
 
Yes the FAST system is speed density.

Don't pay attention to % load. Its merely a calculated value. Think of it this way, while the engine is stumbling its making very little power, in fact hardly enough to keep it running. That's why you see % load so high.
 
Some systems have both MAF and MAP sensors. In the video there's something called "AF" and also "TAF", yet the O2 reading is on a different screen, so those might not be "Air to Fuel". But I just cruised to the FAST website and don't see any MAF systems (just OMG!!! prices). Do you have a Wideband O2? It looks like it's going down to 10:1.
 
Ok, I've got the truck idling like normal but have a concern about it. I recalibrate some of the parameters, including TPS and the idle screw.

While watching the TPS % on the handheld, I noticed a couple things.

1) I can bring the engine from an idle of 700, up to 1050rpm without the TPS reading anything. I get 1% reading at 1050rpm and 00% with anything below. This is easily repeatable.

2) The sensitivity of the TPS is much less while the engine is on verse when it's off.

3) Using my foot and practicing with the throttle, I performed this next one.
From idle position to a throttle point I practiced, I get two different TPS readings, depending on whether the engine is running or not. If it's on, this throttle position will result in a ~8% TPS input. If the engine is NOT running, the TPS reads ~14%. This is also how I can feel a difference in sensitivity, watching the numbers fluctuate while it's off, but while on it's lagging.

:( And now FAST customer service is closed
 
Blue85 said:
Some systems have both MAF and MAP sensors. In the video there's something called "AF" and also "TAF", yet the O2 reading is on a different screen, so those might not be "Air to Fuel". But I just cruised to the FAST website and don't see any MAF systems (just OMG!!! prices). Do you have a Wideband O2? It looks like it's going down to 10:1.
Click to expand...

Yes the system has a wideband O2.

"AF" is actual air/fuel ratio
"TAF" is target air/fuel eatio. Its displayed on a bar graph so you can see how close the engine is to its set parameters.

On other page it displays actual air/fuel in a digital readout so you can see exactly what it is rather than just some unknown scale bar graph. Honestly its not the best interface, but apparently the new 2.0 uses a tablet with a much better and more customizable interface.
 
Seems like the TPS is loose, the throttle blades are loose (probably not - it's probably pretty new?) or there is a bad ground. It would be stupid if the TPS shared a ground wire with something else and wasn't ratiometric, but it's possible. Maybe just check all the grounds and measure voltage from B-, block, ECU, etc. to see if you are getting a shift somewhere. If it used to run good, the basic setup must be OK, but something could have come loose or corroded.

Isn't there a routine to calibrate TPS where you tell it you're at 0% and 100% and it stores those voltages?

So the thing is basically running OK now? What all did you do?
 
Blue85 said:
Isn't there a routine to calibrate TPS where you tell it you're at 0% and 100% and it stores those voltages?

So the thing is basically running OK now? What all did you do?
Click to expand...

I did just this procedure :waytogo: and dicked around with the idle stop screw. I'm going to throw a new air filter on it since the current one is filthy (though all these tests were done without one, so it's not the filters fault). I'm taking it out Sunday locally. We'll see what happens. I'll be calling FAST again on Monday.

EDIT: Oh yeah, and the system only has one ground. The ECM has a dedicated ground from it. The tech signal "filter" has one but it's separate from everything. All sensors either get a ground through mounting or they have a ground wire. Haven't looked closely at those. I'll look over my grounds today.
 
I would guess its a bad ground. I've personally seen this exact thing happen with 2 different friends' vehicles with this system. If the ground is not clean and directly to the battery (same with the positive) it will cause it to idle erratically and not run worth a crap. The IAC values were fluctuating and the thing would not run and they were rich with black smoke. Check the power and ground cables and make sure they are directly to the battery with zero other splices in between or it will cause problems with electrical noise and ground loop issues that you cannot see but will create a nightmare trying to fix it until the main cables are corrected. If you have anything else spliced into the EFI ground or power, seperate it, and run it's own dedicated single wires directly to the battery. As odd as it sounds, it is crucially important.
 
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