EFI troubleshooting-poor idle, stalling, hard restart, etc.

[4WHLFUN]

Ok, ill attempt to describe my symptoms as best as possible, but 1st some details:
Fresh build 302, 351 efi cam, gt40 heads, explorer upper/lower, 21# injectors, 70mm throttle body, similarly sized mustang MAF, A9L, Ford Motorsport harness, Single rail mounted walbro 255 fuel pump. All sensors are new except IAC, MAF, and TPS. No egr or other smog equip. New TFI dist. and Motorcraft cap/rotor. New TFi coil. Original C4. No VSS.

O.k. so on to driveability...After burning up 2 TFI modules I finally get it out on the road. There is no power under load, it coughs spits and sputters and quickly stalls. Early on it would start right back up but the same thing would happen. I could rev it to the moon in park or neutral, but a soon as it goes in gear and has a load it acts like its either starving for fuel or loaded up. I assume the former because there is never any smoke like its overly rich. Also I noticed it would get really hot and heat soak like crazy. I was burning up TFI's so I thought it was spark related. I swapped in a 180 t stat and motorcraft cap and rotor. The plugs were white so i went one step colder.
Back out on the road and I'm cruising along and then out of nowhere shuts off....hit the switch, start, go a few hundred yards, shuts off. This repeats over and over to the point I'm limping it home, not able to get over 20mph and go a few hundred feet with it spitting and coughing and stalling out and now its becoming harder to restart. One thing was clear though, it was holding temp nicely at 180-190. Another new symptom was was idle hunt, especially when cold. So after much head scratching I think I have a fuel delivery issue. I pulled the fuel line at the rail and used the test connection to run the pump and find that my $$$ Mallory EFI pump must be shot because there aint but trickle comin out.
Fast forward to last week and I install a Walbro 255 on the frame and hope for a miracle. I check flow before connecting to rail and it looks good. Hook it up, set pressure to 39, it was close already...and fire it up. Trouble still, it wont idle without help and when it does it hunts up and down 300 or 400 rpm. I pull out and run down the street and it feels good then the SOB just shuts off! Now it wont restart long enough to go anywhere and I'm stranded for the moment. I finally get it to fire and pointed in the right direction to hall a@# back to the garage were it dies as i coast into the stall. I'm completly at a loss, it took 3 years to get to this and I'm losing faith in this build. I've got all this money tied up and I cant enjoy it they way I dreamed. Sorry so long winded, but its complicated...

 

[bronconut73]

You have a killer set up there. Be patient. It is going to be uber good when you fix these little issues.....


Take a deep breath. Don't look at the eb for a few days. It "is" fixable. Do not give up.

 

[xcntrk]

How did you compensate for the 21# injectors, A9L is expecting 19#?

 

[ScanmanSteven]

Whew, that sucks. Not sure I understand burning up the TFIs so maybe someone will help with that. Would you by any chance have access to a spare computer? I've had similar problems, not the TFIs, but computer problems. I've got a computer that randomly shuts the fuel pump off. I added a dash gauge, rather pricey, plus a light to make sure the pump is running. Once I realized the pump was shutting off a lot I changed computers and that problem went away. You also mentioned a 70mm MAF, I'm not sure the A9L is programmed to handle the 70mm. If it isn't programmed that causes running issues. I thought the A9L could adapt to changes like that but it doesn't as well as I thought. Try PMing EFIGuy and see what he thinks of your issues. Do you have any codes?

 

[DirtDonk]

Is this a flat-tappet or a roller cam? And how much cam is it? Does it justify the larger injectors and throttle openings? Agree that to use those larger components (especially along with a bigger cam) you would need to tweak the ECM into working with them. Not sure the details, just that others have had "issues" as well.

Is the harness set up for the manual computer, or an auto? I forget how the Ford Racing harness does that though. For the Ron Francis harness you have to place a jumper into whatever position (manual or auto) matches the wiring pinout of the computer.
But neglecting to do so will fry a computer.

Why not a new TPS, if you have all the other new stuff? Not sure that a bad TPS would cause your issue, but it's a possibility I think. Have you measured the output or ohm reading of the existing sensor to see what it's doing?

If not new, what's the MAF from? A '94/'95 Mustang? Normally you can test a MAF by simply unplugging it to see what it does. But since yours is barely running (when it is running), I'm not sure that would tell you anything.

What about vacuum leaks? Tested for them yet?
What about the PCV valve? Is it connected properly, with the valve in the back of the lower intake and the vacuum tube attached to the upper plenum? And what about the fresh air return? Is it connected to either a hose nipple on the throttle body, or at least a fitting on the intake tube between the TB and MAF?
Is the MAF mounted at least several inches away from the TB?
Using an oiled filter? If so, any chance it's got too much oil and is fouling the MAF?

Just a few queries to get the ball rolling.;D

Paul

 

[4WHLFUN]

Thanks for the responses, I'll try and answer each question.
The cam is a flat tappet Comp Cam XE254H just a bump more lift and duration than OEM Fox 5.0. It is advertised as computer friendly with a 114deg. lobe separation sim. to OEM. I chose the 21# injectors from the assumption(hope) my combo would make close to 300HP. I realize the ECU is tuned for 19# so I thought I would just reduce the pressure to compensate and the larger injectors would run at a reduced duty cycle over the 19's.

I don't have another computer to try, I guess I assumed they either work or they don't. It's definitely worth trying.

The wiring harness is not designed to be auto or manual specific according to the documentation. It works with either computer whether auto or manual.

I have not checked the TPS or MAF output. I assume I would get a code if there was an issue with either. I can check this.

The MAF is from a Mustang as far as I know. I have unplugged it and the motor runs noticeably worse and dies soon after so I guess it's working. The filter is dry and the MAF wire is clean.

PCV is new along with mesh filter in the back of the intake. This is routed to the upper plenum. The fresh air tube is installed from the TB to the valve cover port (OEM Mustang valve covers)

It's been a while since I checked codes, so I will tonight and report back. Thanks Again!

 

[Timmy390]

From the COMP website.........The Xtreme Energy XE254H camshaft is for E.F.I. Speed Density equipped cars and works with the stock computer. It provides very strong torque and excellent mileage with a good idle quality, perfect for those daily drivers.

Not sure that it matter.....but the A9L is Mass Air.

Tim

 

[4WHLFUN]

Good point. I read that as well and I can't believe that the camshaft knows the difference between speed density and mass air...additionally many speed density motors are converted to mass air by various aftermarket companies.

 

[xcntrk]

I suspect you're going to need a tuner chip and some adjustments to the ECU to work with your specific setup. The problem you need to get to the bottom of however, is if you have any mechanical issues (as Dirtdonk described) before messing with the tuning. You want a solid and stable motor setup before applying a base tune.

 

[DirtDonk]

And raise that fuel pressure back up first too. It's important for the fuel atomization.
Let the computer do the figuring on duty cycle and all that stuff, based on what it sees at the oxygen sensor(s).

Paul

 

[DirtDonk]

...The cam is a flat tappet Comp Cam XE254H just a bump more lift and duration than OEM Fox 5.0. It is advertised as computer friendly with a 114deg. lobe separation sim. to OEM.

sounds like a great cam. The reason I asked what type was to find out if you had performed the critical cam break-in procedure upon initial startup. If not, some or all of your symptoms could have been due to a wiped out cam.
Some people get away without doing the break-in, others not so much.

So did you do a cam break-in?

I chose the 21# injectors from the assumption(hope) my combo would make close to 300HP. I realize the ECU is tuned for 19# so I thought I would just reduce the pressure to compensate and the larger injectors would run at a reduced duty cycle over the 19's.

I don't think 21 is a bad assumption. Seems like a reasonable size for a 300 hp engine, but I think even the 19's could have probably handled it.
That said, I don't think reducing the fuel pressure is the way to go for any of this type of tweaking. Just too many things rely on certain pressures, such as correct atomization, and probably flow expectations too. But I know none of that. Just "assumptions" on my part at this stage.
But they seem like reasonable assumptions too, to me.

I don't have another computer to try, I guess I assumed they either work or they don't. It's definitely worth trying.

Many times that's the case. They fail, the engine stops, end of story. But it's often enough that they merely run like crap that you have to still take the possibility into account. The whole auto-vs-manual thing with the other types of harnesses burns one particular trace on the circuit board and does not always end up in a non-running engine. Just a crappy running one.

The wiring harness is not designed to be auto or manual specific according to the documentation. It works with either computer whether auto or manual.

I heard that just recently and am very curious how they take care of that. Maybe the Painless harness is the same way, since I don't remember any specifications about that. But a modified stock harness, or a Ron Francis (old RJM) harness requires a re-pin or a flipped jumper wire to keep things working properly.
Maybe you, 904Bronco, or one of the others that have used this Ford Racing harness can shed some light on how it's done?

Hope you get yours dialed soon so you can enjoy that sweet sound of success(fully running engine) sound.

Paul

 

[DirtDonk]

...The Xtreme Energy XE254H camshaft is for E.F.I. Speed Density equipped cars and works with the stock computer. It provides very strong torque and excellent mileage with a good idle quality, perfect for those daily drivers.

Not sure that it matter.....but the A9L is Mass Air.

That's a good call Tim, but I don't think it matters as much as they make it sound. What (I think) they should have said is that this particular cam is compatible with the much more finicky Ford Speed Density systems, whereas many cams that might be swapped in are not. But should not necessarily have made it sound like it's good for SD systems only. Which is what it sounds like from the way they wrote it up.

The Mass Air systems are not as particular and can compensate for mild cam changes much better than an SD setup can. Including some with much larger increases in lift and duration than the 254 has. So it's probably an OK swap. The 114 angle is just what an MA setup likes to see as well. And being basically just a step up from stock, it should be a good truck cam I would think.

At least I hope so since that's very similar in specs to what I'll be running!

Paul

 

[nvrstuk]

Painless Harness spends about 3 pages talking about how critical is it to make sure you wire the harness specifically for either the auto or the manual but it can't work for both!!! you could have a fried ecu because of incorrect wiring for the auto/clutch no-start circuit.

Painless makes it very clear that improper wiring of this circuit will burn out the ecu.

Hope you get this up and running soon!

 

[EricLar80]

My best advice for you is to bring these things back to stock configuration:

- MAF should be 55mm
- Injectors should be 19lb/hr
- TB should be stock

Also double check that you have the TPS installed correctly. Just make sure it is below 1V with the throttle plate closed, and you reset the computer when done.

From there you can more easily diagnose if you actually have a problem somewhere else, or if the mismatched components with the stock tune is the issue. Once you get it running properly then you can attempt to bring the mismatched parts back in and see if it helps performance.

Fuel pump is definitely not your issue with the spitting and sputtering. It is definitely related to the MAF saying one thing, and the injectors delivering something else entirely. You should not just swap these out without a tune, no matter what people seem to think works. The function of those two items are so important in the computers tune and messing with them without a new tune is asking for problems. I learned this the hard way... There is a reason a I have a lot of spare fuel pumps, ignition components, and sensors when all I really needed to do was either tune the computer for the custom parts or go back close to stock. I opted for the latter with a nice cam and could not have asked for a better running motor.

Regarding the TFI - which distributor did you put in? It is an MSD/aftermarket, or ford original?

Eric

 

[xcntrk]

Where did you get 21# injectors anyway? I thought the Mustangs went from 19# to 24#?

I was going to suggest there's an alternative to get a "tuned" MAF for your upsized injectors but those only appear available for the 24# sizes.

 

[Timmy390]

The more I read about pin #30 and the issues it will cause if hooked up wrong the more I'm thinking it's your problem. And if it IS wrong, the ECU might be fried.

You're running a A9L so I'm guessing you have a manual transmission. You have to splice into pin 46 (Signal Return) which is a ground and run it into pin 30 which tells the ECU the transmission is in "neutral". Also the issue with it shutting off and not wanting to run is also a symptom of pin 30 miswire. As I understand it, once the temp hits around 170, the shutting off starts.

The "hunting idle" sounds like you have 12 volts to pin 30 so it thinks it's an auto trans.

I think you've "Jedi mind tricked yourself" (happens to the best of us) on the injector deal. I did some reading and understand what you're trying to do but it's more complicated than just adjusting the pressure. Go back to 19# and put the pressure back to stock and eliminate that as the issue. Junkyards are full of 19# and a quick cleaning is all most need. I grabbed a set (the fat ones) the last trip to the yard just to have an extra set if needed.

Tim