Help with erratic fuel pressure, inline pump needed (desperate) - Third Generation F-Body Message Boards

Ryan3834me · 06-10-2007, 06:47 AM

I recently swapped out a 305 TBI system to 383 TPI (30lb SVO injectors, ZZ4 cam, L98 heads, AFPR). I first ran stock TPI 'off the shelf' in tank pump. Pressure would fall from 42 to 23 as engine was revved.

Not, wanting to pull tank pump, an inline MSD pump was added. Fuel pressure was irradic (needle bouncing from -8 to +8 of setting of 43 lbs). Stock 350 prom saying MAF (33 code), running rich.

Week later I get a chip I ordered from Fastchips, with new specs for 383, ZZ4, 30# injectors, etc. I install chip and find it sets no code for MAF (disconnected or not, weird, but for another forum). The fuel pressure since I returned to project, in inexplicably now in the 20# range. I adjusted AFPR to get irratic high 20's. Key in off position pressure in system drops instantly to zero. I purchased new fuel pressure gauge, since drop in pressure was inexplicable, since, I assume car wasn't monkeyed with since I was away from it for a week. New gauge said same as old one.

Yesterday, I had removed in tank pump, and replaced it with a std. 3/8" filter. I installed (replaced) a new inline MSD fuel pump. I had suspected that the restriction of an in tank pump may have caused both pumps to fail. Pressure is now wildly pulsating around a mean of about 45 (+/-) 20 lbs!!. When I rev engine pressure does become less erratic (+/-) 6 lbs.

I have never seen this kind of erratic shaking of a fuel pressure gauge before.

The vaccum line for the AFPR (for now) is disconnected, and there is no fuel coming out of it.

The 30lb injectors were new. (for anyone reading, note the SVO injectors must have grove cut in them for retaing clip, or fire may result). I thought maybe one or more was stuck open. I suspect maybe AFPR is bad, or inj are bad. I can feel a vibration in the fuel pressure gauge hose, consistant with the wildly flickering readings. What am I overlooking, where do I go from here. I badly want this problem gone. I can't even tune this, without consistant fuel pressure. It should always be close to a near solid and steady reading, right? (vac line disconnected).

Thanks!

Ryan3834me · 06-11-2007, 05:47 AM

Update,

Well I replaced the FPR diaphram and spring ($40 - autozone), and now have a steady fuel pressure of 42 lb. Yey! Thank god new intake gaskets didn't do any bonding yet.

Now to fix the rest of the ghosts in the machine.