EFI issue for discussion

[Sporto]

Hey CB,

I am looking for some insight to an odd issue with my EFI on my EB.

Background: Old 302 converted to Mustang MAF EFI with A9L computer about 12 years ago. Stock everything, coil, TFI and distributor. External E2000 HP fuel pump, fed by LP Carter near tank. Has run flawlessly for thousands of miles.

Issue: Recently, and Intermittently, usually when idling after warmed up. It will suddenly drop from 750 RPM to 600 or so. It's noticeable. I have an AEM wide band sensor and gauge installed, and at that moment it goes from ideal 14:7 to off the scale lean. When I begin driving it this way, the lean condition continues through the gears, and it just seems like it could stall out, and die but it usually makes it home.

When I restart it, everything is back to normal until that happens again at some point.

What I have checked.
1. No codes or CEL,
2. I have a fuel pressure gauge on the rail, and it is steady around 38psi or so at all times.
3. I checked vacuum and it is steady and in tolerance.
4. Timing is set to 10 degrees advanced with SPOUT connector out.

Engine runs fine whenever not in this odd "limp mode", so I am thinking O2 sensors, MAF, or Air Charge sender. Or worse the computer. I don't want to throw parts at it if there is some possible experiences on here that others may share that could help me sort this out.

Thanks!

Rich

 

[SevenT]

Contact EFI Guy on the forums. Garry may have some insight. Good luck

 

[surfer-b]

I would start by replacing the diodes in the A9L PCM

 

[Timmy390]

I would start by replacing the diodes in the A9L PCM

I agree.....Crack it open and take a look at a minimum

Tim

 

[Sporto]

Cool, I have one of the Cap replacement kits, that I have not gotten around to replacing, but I am not sure what I would be looking for with diodes. Anything that I should be looking at?

 

[Timmy390]

Cool, I have one of the Cap replacement kits, that I have not gotten around to replacing, but I am not sure what I would be looking for with diodes. Anything that I should be looking at?

Diodes.....

Tim

 

[73azbronco]

fuel pressure when it does this?

 

[Sporto]

fuel pressure when it does this?

That is what I thought too, I swapped out the fuel pump and back blew the lines with compressed air. What is odd, is it just happens at any time out of the blue. Then it goes away if I shut off the engine and restart it a few minutes later. That is why I was thinking it may be related to something digital. I will keep an eye on my Fuel Pressure though.

 

[Sporto]

Thanks for the info on diodes. I am going to send the computer off to someone who knows the deal. and can fix it properly. These things are too expensive to screw up.

In the meantime, I am going put my other can of worms on the table and open it up.

I also have a PNP MegaSquirt ECM that I installed at one point, and it ran okay aside from the fact that I could never tune it to run as well as the OEM MAF computer. Too many headaches with all of the software and the AFR tables etc... It was a fun project, I looked all badass riding around town with my laptop on the front seat collecting data and autotuning the computer as I drove. I had my little Android tablet connected to it, showing me all the cool data feeds that I really didn't totally understand. (Yeah, I admit that) Hwoever I did enjoy learning a lot of that engine science stuff, but in the end I just want to drive my Bronco without all of that tuning drama, so I uninstalled it went back to the OEM computer. The same one that now seems to be giving me a hard time. I still have that ECM in a box in my shop, and I am tempted to reinstall it and start messing with it again. LOL Not sure I want to invest in a dynotune though, so I would just keep letting the software do its autotune thing until I had a decent running reliable engine again. If that's possible.

Any input from my fellow CB community? I do enjoy the discussions on here whether I participate or not.

Another Bronco guy asked me years ago why I was going through all the trouble to convert a stock, daily driver Bronco to EFI away from carb. It did not make sense for my application, and I just said "it looked like a fun project."

Well here we are!

Rich

 

[Broncobowsher]

Diodes? I thought it was the caps that went bad in the computers. I guess I just learned something new.

 

[DirtDonk]

I thought that when the capacitors started breaking down, the first clue was that the fuel pump stayed on when you first turned the key on. Instead of cycling for a second and then shutting off.
Is that then, not the only symptom?
I don’t remember hearing capacitors is blamed for what you’re experiencing before.

Have you tried wiggling wires at the BAP and TPS and other areas? Have you renewed (not just rechecked) your engine to body ground and battery to body grounds?
Obviously the main engine ground is fine because otherwise you wouldn’t be able to spin the starter.

 

[DirtDonk]

Oops! They said diodes, and I was automatically thinking capacitors.

 

[bronco italiano]

Diodes? I thought it was the caps that went bad in the computers. I guess I just learned something new.

If I recall correctly, it is caps and diodes. I had EFI guy do mine after 8 years and he said it was time as they were just starting to leak

 

[DirtDonk]

What happens to one of these engines when a PCV valve starts to fail? On carbureted engines the most common failure is just getting gunked up. But PCV valves do wear out over time as well.

 

[DirtDonk]

Capacitors leak, but never heard of a diode leaking. However, that doesn’t mean Garry, doesn’t know something about diodes, and only mentioned leaking because the caps were. Maybe?

 

[surfer-b]

I should have stated the Caps also, I have had both go bad on those old PCMs

 

[73azbronco]

mount a a fuel pressure gage so you can see it from inside cab while you drive, mounted on hood of course, do not route it into cab.

Yes, it could be computer causing fuel pump to hiccup. But monitoring fuel pressure lets you know what it's doing. No fuel pressure issue would make me think next step is injectors or what controls injectors followed by IAC issues, odd intake leaks, etc.

Do you have a spare A9L to try ?

 

[DirtDonk]

Haven’t heard of TFI problems in a long time. Maybe it’s about time one of those cropped up.

 

[Sporto]

I am going to inspect the caps. Since that is the easiest to do.

I don't have any other OEM computers to test against.

TFI issues, I do have a spare distributor that I know works that I can test against as well.


Thanks for this info.

 

[Broncobowsher]

Lean doesn't always mean a fuel starvation issue. Lack of ignition will send unburned air and fuel into the exhaust and that air will show up as lean.