Surging fuel pressure

[BennyD]

Hello, have been reading the forum for a year and a half to try and find a fix to this issue. I will get 20-60psi fuel pressure if I put my foot into it, still fluctuates 35-45 under normal acceleration. Photos below of the high and low during normal acceleration. I have videos as well. Any help is appreciated. Did all the normal stuff. Plugs, wires, vacuum lines, Vam cleaning, TPS. Thanks!

[BennyD]

Idles dead on 40 psi and 1000rpm, starts every time.

[Erics SVO]

When you say "normal" stuff, was the fuel pressure regulator included in that? Also, any mods, what about the fuel pump age. What year SVO? Had the car sat for any lenght of time?

[BennyD]

Just did FPR last night, still need to go for a spin to see if any difference. 1984, not sure of fuel pump age but it was swapped when fuel lines were replaced before the car sat for a few years in a barn. Leaning towards pump, feel like I have done everything else. Still finding potential electrical issues every now and then when I really start digging. Just want to rule everything out before I drop the tank. Thanks!

[Erics SVO]

Now, did you do both pumps? OR if you did single in tank change, did you clip the resistance wire out? I'd figure those questions out

[svono50]

Just replied to your other thread, see my suggestion there. Eric is on point to looking over the pumps and that resistor wire too.

[BennyD]

Thanks guys will report back!

[BennyD]

Was able to go for a spin tonight after doing the FPR the other day and checking timing and TPS. Problem persists but seems to only happen early in acceleration now. Once I get above 10lbs of boost the issue tapers off and pulls hard the rest of the way. Still haven’t tried jumping the pump but will try to do that tonight and check the resister. Unfortunately, I did not do the fuel system work. My uncle did and he has since passed away. All the trouble shooting I have done is with no real baseline of what has and hasn’t been done besides what I can see. Have a coil and and module to replace as well. Will report back thanks

[BennyD]

Out for another quick drive and just taking notes. Above 10lbs of boost fuel pressure will not go above 40lbs. Once I get out of the fluctuations it levels out at 40 regardless of boost level

[svono50]

Out for another quick drive and just taking notes. Above 10lbs of boost fuel pressure will not go above 40lbs. Once I get out of the fluctuations it levels out at 40 regardless of boost level

Definitely sounding like a fuel pump related issue. With the non-running fuel pressure checking method I noted, you can try squeezing off the return line for just a quick second. It should register something north of 90psi. If not, you need to figure out what the issue is back at the pumps. Start with the voltage at the pumps to ensure you have full power before throwing new pumps at it.

[Corrugated]

Check the small 's' shaped fuel line at the pump, in tank...common to wear / leak / split....

[svono50]

Check the small 's' shaped fuel line at the pump, in tank...common to wear / leak / split....

That was one of my thoughts, once voltage is verified good, certainly a common item to split and limit pressure.

[BennyD]

I think I found the issue I THINK. Dropped the tank to find a 255 pump, which confirmed my thoughts that the system had been upgraded some time ago. Tank full of dirt and debris and sock not looking so hot. Replacing tank, pump, sender and harness. Question: was the resistance wire spliced at the factory? May have been my problem all along like mentioned above. Unfortunately just got around to doing all this…wife and kids out of town! See pictures of the crumbling mess

[svono50]

Somebody correct me if I am wrong, but I think the 'dual pump' setups had a resistor wire going to the in-tank, low-pressure pump(??). Swapping over to a single in-tank pump, from what I remember, requires removal of said resistance wire to all full voltage to the in-tank pump. Having only owned an 86, I can't say for 100% certainty.

I will say that the wire you show is 'sketchy' at best and needs to be replaced as part of the problem. As you already noticed with the dirt/debris in the tank you would be best served with a fresh system. Make sure you flush the lines and may even want to consider having the injectors cleaned. Good catch before popping a head gasket or worse!

[Erics SVO]

It's a tad tough for me to tell from the pic. If that wire has what looks like a simple silver non-insulated crimp holding the 2 wires together that is the resistor wire. I'll have to look up what the wire color(s) are. As its been many years since I clipped it on my 85....