Awolfgangb

Hello all, my name is Andrew I live in Indiana and I've been browsing this site for a cpl years now. This is my first post. I have a 95 z/28 that has low fuel pressure, believe it was 34 psi last time I checked. She will studder sometimes on acceleration like the engine is being starved for fuel, when I press down the gas pedal more though she powers through it.

I have already replaced the pump with a racetronix walboro unit, and put a new fuel filter on. Also replaced the regulator, it was either an Ac/delco or delphi unit I can't remember. MAF has also been cleaned recently.

I have the datamaster and tunercat programs, and i just installed EEHACK and am installing the free scanner program I found on this site as i type this. I must admit that I am a noob when it comes to reading the results of the datamaster program. I tried to upload a datamaster file I have saved but it says it is an invalid file. It is a .uni type file. Anyone know how to change the type of file so I could upload it?

Injuneer

When you checked the fuel pressure, did you take the vacuum compensation line off the fuel pressure regulator? If not, pressure in the mid 30's is normal. With the vacuum line off, pressure should be 43.5 PSI, with GM spec accepting a range of 41 - 47 PSI. When you reattach the vacuum line the pressure will drop about 8 PSI with a stock cam, a bit less drop with a more aggressive cam.

The purpose of the vacuum line is to maintain the DIFFERENTIAL pressure between the fuel rail (positive gauge pressure) and the intake manifold (negative gauge pressure) at ~43.5 PSI.

Injuneer

Datamaster has an export file option. By exporting in .csv format, anyone can open the file with Excel. If you keep it as a .uni file, only people with Datamaster can open the file.

When you use the export option, you have to specify the range of the records you want to be exported. Enter "1" for the first record, and the number of the last record in the Datamaster log as the number of the last record to export.

You also have to enter the data fields you want to export, and the sequence in which to export them. I have a list of the recommended fields to export, and the sequence. I can post it when I get back to my PC, later today.

Awolfgangb

Thank's for the reply. Yeah it was 34psi without vacuum. I'll try and get that daltalog to upload later tonight when I have more time. Been moving this weekend so things have been pretty crazy. At this point I am contemplating just taking it to a shop so that way I can hopefully get the new tranny in this weekend. That warranty is going to waste just sitting in the garage haha!

Injuneer

34 PSI means you are forcing the long term fuel trims to add 11.6% fuel to make up for the shortfall. Pointless to run a data log with low fuel pressure.

Awolfgangb

Ah gotchya, well I will post an update once I figure it out.

GaryDoug

Scabn9495 can import uni files (most versions). It can then save it to a csv file as usual. That way you don't have to select items to export; Scan9495 gets and saves it all.

https://www.mediafire.com/folder/gon...T1-V8%20folder

GaryDoug

Upload it with the .txt extension, then I can get it, change it back to uni, import into Scan9495, and post it in csv format.

Injuneer

Have you checked the voltage available at the fuel pump when it is running?

When the fuel pump primes and shuts off (key in "run"), how long does the pressure hold at 34 PSI?

Awolfgangb

Thank man i will check it out. I ended up taking the car to a local shop to have them put it on a lift and check for kinked lines or whatever could be the source of the low fuel pressure. They checked all the lines and said everything was good, also hooked up their gauge and said the fuel pressure at idle was 45psi and under load it was 54psi. So maybe my gauge is off? It's pretty old my dad has had it for a while.

They asked if I was experiencing any symptoms and I told them about the intermittent lack of power, seemingly fuel starvation. They said to check the voltage then. Went ahead and ordered a new coil and icm because I don't know when the last time if ever they have been replaced, been on the car since I've owned for a cpl years. Also ordered a new knock sensor and o2's per Solomon's advice that came along with the tune. Performabuilt lvl 2 with 2800 stall, Solomon tune, and all the previously mentioned parts should be installed before the weekend, hopefully with great results. Will post back with updates. Thanks again for all the info guys.

Injuneer

54psi under load is too high. That would mean the injectors are spraying 11.4% more than their design flow. Something is wrong with the system if the pressure is that high. My first reaction is you must have an Aeromotive AFPR, but your initial post indicates the replacement was AC Delco or Delphi.