I'm about to pull my plenum to upgrade my injectors and the first thing to do is relieve fuel pressure, however my cars battery is dead and the cars been sitting for a few months. Last time the engine was cranked was for a compression test, and it hit me today that I forgot to pull the fuel pump relay when I did my compression testing. Oops. Should I be ok? Fast response appreciated, literally ready to pull right now.

If fuel got into the cylinders while compression testing, then you didn't get the right readings and yeah- I'd do it all over again to ensure you get correct readings.
You CAN cheat the relay by using vice grips carefully over a rag and the fuel line after the filter, to clamp off the fuel from entering the engine- obviously don't crush it, carefully clamp the line and run the engine until it dies, and then do your tests.

DCaff300ZX wrote: ↑

Wed Oct 17, 2018 6:50 am

If fuel got into the cylinders while compression testing, then you didn't get the right readings and yeah- I'd do it all over again to ensure you get correct readings.
You CAN cheat the relay by using vice grips carefully over a rag and the fuel line after the filter, to clamp off the fuel from entering the engine- obviously don't crush it, carefully clamp the line and run the engine until it dies, and then do your tests.

I'm not worried about cheating the system, the relay just pops right off. I was just wondering if there's even fuel pressure in the system at this point. My battery is completely dead so I can't crank the engine to release the pressure that may or may not be there either way

If the car has been sitting for 2 months, I doubt that there will be any pressure. Just wrap the connection to be disconnected with a couple rags while pulling the hose off.

Highly unlikely the fuel affected compression checks. More likely to foul the plugs, and the reason you pull the relay, as well to not overload the cat with unburned fuel at a start, it kills the cat pretty easy.

amc49 wrote: ↑

Thu Oct 18, 2018 12:34 am

Highly unlikely the fuel affected compression checks. More likely to foul the plugs, and the reason you pull the relay, as well to not overload the cat with unburned fuel at a start, it kills the cat pretty easy.

hey amc are you pretty knowledgeable in these cars or engines in general? Im in dire need of some advice from anyone who isnt a total noob (me)

amc49 wrote: ↑

Thu Oct 18, 2018 12:34 am

Highly unlikely the fuel affected compression checks. More likely to foul the plugs, and the reason you pull the relay, as well to not overload the cat with unburned fuel at a start, it kills the cat pretty easy.

Well, you shouldn't have the plugs in for compression test anyways; so how would the fuel affect the plugs?
The fuel being sprayed in the cylinder of test may show slightly higher number. If all seals are good in that cylinder and you excessively crank the starter(pushing lots of fuel in), you "may" hydro lock the engine.
I doubt it will happen, but possible.

'...how would the fuel affect the plugs?'

You got me and my bad there. 65 years years old now and some alzheimers........some people though do not pull all the plugs. Wrong of course. You have to pump at least enough fuel in to take up compressed displacement, and pretty much impossible but some can build up to wet the piston tops to possibly foul plugs put back in. More of a danger catching car on fire if some plug lead is left sparking in the open to light off the combustibles being pumped out of other cylinders you are not testing. And it doesn't take much to poison the cat, it then overheats from excess fuel to melt the matrix inside.

I worked on engines in general of all types and not these although I have two Nissan now that I have transitioned from Ford. I do all work 100%, nobody else ever touches my cars and that way for 40+ years. That way I can't blame others for poor work and not an issue. I am a super picky perfectionist S-O-B........it's a curse.

Fuel pressure if sitting drops after a while, a few very odd cars might not, easily relieved by simply wrapping a towel around any fuel pressured part and simply loosen it to a leak then tighten it back up. A pressure takeoff may be provided to check pressure; often you simply push the valve in like a tire stem. Nowadays though they are often removing them, it makes the pressure only checkable by software and more dealer work then. It's about saving more weight and the 50 cents the fitting costs to give more money to the CEO.

I sent you guys pms about this issue cause I re tested with the fuel relay removed and now I have compression issues