Thanks for the input. It does have the ability to datalog. I haven't done that, yet. I still need to change the fuel filter. I can't remember if I changed it when I did the bumper swap. If I didn't, it's been on there a while. Then I can do the datalogging. After that, I can send the info off to Affordable Fuel Injection for a different map.

That makes sense.

Steve,

Can you tell when you lose power, does it happen rather fast right after you encounter a load, or is it delayed a bit? My thinking is that if the problem is the ECU map then the lean condition might be fairly quick & responsive. However, if it's the filter then it may take a bit for the filter and associated fuel rails to lose pressure. Fast and slow here are relative terms or course, and this is just conjecture on that one problem would behave opposite the other.

If I had to guess, I would say that the fueling tables are just a bit off, but I do think you are on the right debug path with changing the filter first. The filter is easy to change and could quickly rule it out as culprit or contributing factor. Sorry, I'm not familiar with the GM fi operation so I'm not much help there. I would definitely datalog the AFR if possible. You lose power faster when you fall off 14.7 in the lean direction, but the same thing happens on the rich side too (just have to be farther away). It's possible your tables are too rich under load. If possible, switch off the car right after the event and check the plugs. Any backfires under load?

Len

2 hours ago, superlen said:

Steve,

Can you tell when you lose power, does it happen rather fast right after you encounter a load, or is it delayed a bit? My thinking is that if the problem is the ECU map then the lean condition might be fairly quick & responsive. However, if it's the filter then it may take a bit for the filter and associated fuel rails to lose pressure. Fast and slow here are relative terms or course, and this is just conjecture on that one problem would behave opposite the other.

If I had to guess, I would say that the fueling tables are just a bit off, but I do think you are on the right debug path with changing the filter first. The filter is easy to change and could quickly rule it out as culprit or contributing factor. Sorry, I'm not familiar with the GM fi operation so I'm not much help there. I would definitely datalog the AFR if possible. You lose power faster when you fall off 14.7 in the lean direction, but the same thing happens on the rich side too (just have to be farther away). It's possible your tables are too rich under load. If possible, switch off the car right after the event and check the plugs. Any backfires under load?

Len

Len,

Considering I don't have much experience performing diagnostics on FI, your input is greatly appreciated. I hope to change out the fuel filter this weekend and test, weather permitting. First, I'll test in the garage to make sure I am data logging. The software wasn't designed for an operating system as advanced as Windows 7, so I might have to find a refurbished XP machine. Once I confirm I can log data, I will go for another drive, and I will try to note the time response. Like so many others on this board, I'm not a spring chicken, so I'm not going to rely on my memory about whether the power loss was fast or slow. However, I don't recall hearing any backfire, and that I'm more sure about.

Considering the fact that my engine is not stock (2.8L with higher compression and possibly a non-stock cam), it could also be a combination of filter and map. It helps to keep in mind that with the SUs, I previously had issues with being a little lean toward the top end and used 1/3 racing gas to help prevent detonation.

By the way, welcome back.

Have you tried the crude but effective "fuel pressure gauge hanging out of the hood" method.  Real-time pressure readings will tell you if the filter is clogged.

Thanks,

The time it takes to bog may be a red herring, but I would be interested if you can detect anything. The FI filter is much more fine than a  carb version of course, so it may not take much to cause issues. Hopefully that will cure a majority of it.

Zeds idea is good and would be useful, a bit scary perhaps. ?

Len

Edited August 23, 20195 yr by superlen

I zipp tied mine to the driver's side windshield wiper and it worked great.

 

On 8/18/2019 at 5:33 PM, SteveJ said:

It wasn't having issues before the conversion. I drained the tank completely a couple of years ago for the bumper conversion, and I didn't notice much in the way of debris in the gas I drained out. Of course, when I look at the filter carefully post change, my opinion of the condition of the tank could change.

@SteveJ - I haven't been following this as intensely as I should, but did you change the tank to a later '75-76 tank for FI applications?

6 hours ago, Zed Head said:

Have you tried the crude but effective "fuel pressure gauge hanging out of the hood" method.  Real-time pressure readings will tell you if the filter is clogged.

Actually, I was contemplating a less redneck way of doing things (though it would be untrue to my roots) and buying a sender and a gauge for in the cabin. At this point, $100 isn't that much more to spend.

1 hour ago, wal280z said:

@SteveJ - I haven't been following this as intensely as I should, but did you change the tank to a later '75-76 tank for FI applications?

I'm not sure it is critical to have the baffled tank. The problem still happened with a full (and I mean FULL) tank. The baffled tank wasn't mentioned on the Patton Machine thread on HybridZ, and Rick Patton doesn't mention it on his website. Keep in mind that his primary customers are British car owners. 

This system also operates on a lower pressure and lower flow than the Bosch based system in the 280Z.

I once had a suburban I was datalogging. The fuel pressure gauge was wrapped around the drivers mirror on about 4' of hose. Very convenient ?

Well, I found that I'm missing the driver to use the USB cable to log data. My computer didn't like the CD that the driver was on and fouled it up, so I ordered a new driver. The fuel pressure gauge should get here tomorrow. I replaced the fuel filter and took it for a spin. I am more convinced that it's a fuel delivery issue more than an ECU map issue. The car drove smoothly for a few miles and then started feeling down on power and bucking. I got it home and looked at the plugs. They looked great. I got in the car again and took it to the end of the street. I started in 1st and wound it up to 4,000 RPM. Then the RPMs started going down. I didn't cut the old filter open, but the gas coming out of it looked clean.

I'm going to do another round of testing when I can collect more data, but I'm starting to lean more toward a surge tank.

So it's not the fuel pressure.

I finally set up the fuel pressure gauge (electric - not hanging out from under the hood) and did a test run. The fuel pressure read 15 PSI on the gauge. After just over 5 miles, it started doing the usual routine of acting like it's not getting enough fuel. However, the fuel pressure stayed solid at 15 PSI. I bumped up the fuel pressure to 18 PSI and tested again. Not much changed, but I started playing with the choke lever, and that did relieve the symptoms to a small extent.

I have the driver for the USB cable, so the next test will be with data logging.