Reddragon88gta

New to the forum, just got 88' GTA and am having trouble with fuel pump coming on when engine is off sometimes. Will cycle for a few seconds and that's it. Have replaced fuel filter and fuel pump relay and just disconnected oil pressure sensor and oil sending unit...still doing it. Also when this occurs car takes a while to start and can smell gas odor. Problem comes and goes, any help would be greatly appreciated.

GeneralDisorder

iTrader: (1)

The fuel pump is supposed to run for a few seconds when you turn the key to on. This is controlled by the computer which uses the fuel pump relay on the firewall to cycle the pump on before and durring cranking. After that the oil pressure switch takes over.

GD

Reddragon88gta

Thanks for the reply, but this happens when the car has been shut off with no key even in the ignition, happens like every 10 to 15 minutes.

Dyno Don

iTrader: (7)

Anytime the oil pressure is 4 PSI or more the switch stays closed, after a few seconds it drops.

RBob

iTrader: (1)

Good possibility it is the ECM. Unplug it and see if it still occurs.

RBob.

Reddragon88gta

Thanks for the replies, which oil sensor is that? The one by the oil filter or the one by the distributor? The car has yet to throw a trouble code which is odd but once the car gets going it generally runs good and is responsive but sometimes has more pep than other times

rgauder

iTrader: (1)

Loose battery connection? I just put a new battery in mine and heard it come on while I was hooking it up.

Reddragon88gta

Battery is pretty recent and I actually had it out when I first got it to resecure the battery mount. I reconnected both terminals so they were good. It's the weirdest thing having the fuel pump cycle while the car just sits there with not even a key in the ignition

GeneralDisorder

iTrader: (1)

Well the ECM on these are prone to cracked circuit boards, etc.

After unplugging the oil pressure switch and verifying it isn't that, next up is the ECM itself. If unplugging that does the trick you need a replacement unit. They updated the MAF units at some point. I got a reman new in the box off eBay for $86 for my 86 TA.

GD

Reddragon88gta

Where is the ECM located on this car? And when should I unplug it ? Before or after start? How will I know if the ecm is the problem I.e will it not run etc.?

Reddragon88gta

Before I disconnected the battery I unhooked both connectors off both oil pressure units and that pump still cycled with the engine off and no key, leads me to believe it's not the oil pressure sending units

paulo57509

I believe it's normal behavior for the pump to run a bit after engine shut down. The pump in my car will run for a bit after engine shut down; sometimes it won't run after shut down. It's always done this. Never gave it any thought or tried to characterize a pattern for this.

Looking at the fuel control schematic for L98's and LB9's, the oil pressure switches/sensors aren't part of the fuel pump circuit (unless things changed in 1988 model year).

I believe your hard start problem is elsewhere.

Reddragon88gta

That's interesting, I've never had a car do that. What struck me as odd is that it kept doing it every 15 minutes or so for a couple hours and it hadn't done it before like that.

GeneralDisorder

iTrader: (1)

No that is not normal for it to fire up the fuel pump 15 minutes after shut down. Definitely something wrong with it.

GD

paulo57509

Sorry. I missed the part about the pump running briefly every 15 minutes for two hours.

RBob

iTrader: (1)

The ECM is under the dash on the passenger side. If stock it will be a silver aluminum box, a re-man might be painted black.

After turning the engine off unplug the ECM (two connectors). See if the pump stops doing its run for a moment thing.

Note that the engine won't run with the ECM unplugged.

RBob.

Bob88GTA

iTrader: (2)

Sounds like the fuel pump/relay is "hot wired" and when it senses low pressure in the fuel rail after injectors leak down, it fires up the pump and re-pressurizes the fuel rail...IDK,weird for sure.
It'd be like turning the key to "ON" and you get the 2 second pump run till fuel rail is charged

Reddragon88gta

That's exactly what it feels like, I reconnected battery after cleaning fuel pump relay terminals, they were covered in grease. Car ran very strong with no start up issue and even restarted good after the ride but remains to be seen if it's right

Reddragon88gta

Also noticed two wires that look spliced and non factory near top of engine near firewall. Will upload photo soon. I checked and they have power to them with key off.

Reddragon88gta

Here is the strange looking connection
Here is the unknown connection

GeneralDisorder

iTrader: (1)

Where are the wires going? That's some fugly wiring job. Not weather tight. Needs to be redone properly with a weatherpack at the very least. Probably shouldn't be there at all. Definitely time to figure out what that's doing and correct it even if it's not related.

GD

Reddragon88gta

Next time I work on it I think I will disconnect those jacked up wires and see what happens before reconnecting them right, could be my problem

Reddragon88gta

Did some work and more thorough trouble shooting, I figured out those jacked up wires look like they were once the plug for the interior blower motor and it commonly melts/ watts from heat and that was problems a repair for that. Cleaned them up and reconnected.

Now my fuel pump is no longer cycling after shutdown, but I noticed that my hard start issue is only after the car is warmed up and has sat for an hour or so. Car starts great when cold or if only a short time after it's shut down... replaced the coolant temp sensor but no improvement. Leads me to believe the injectors are leaking and flooding it??? The car only has 77k but had sat a little while before I got it and the injectors look original.

Reddragon88gta

Also when engine is cranking when hot have to blip throttle to get it to catch...almost like by doing that it clears out the flooded gas. Car also smells rich and puffs a little smoke upon start up. When cold car starts great.

GeneralDisorder

iTrader: (1)

The injectors could be leaking down. Put a gauge on it (shrader on the fuel rail) and check for pressure drop after shut down. The factory TPI injectors were not great. If you need injectors - highly recommend Southbay injector. They are a forum sponsor and many of us have used them with excellent results.

GD

Reddragon88gta

Trying to track down a fp gauge, you guys have had good luck with those injectors from South Bay? Are those remanufactured? I liked his prices and the fact they are Bosch, a mechanic recommended accels from summit or jegs and not to mess with remans.

IROCThe5.7L

After it sits an hour and you know it's not going to want to start. Put the gas all the way to the floor and start the car. If it starts faster your injectors or FPR is leaking. I had the same issues with 65,000 miles and my injectors were leaking.

Reddragon88gta

Finally had a chance to test it out, after hot and let the car sit nearly an hour after shut down I cranked it again and while cranking I floored the gas pedal it started and idled high a few seconds and then smoothed out. Exhaust was smoky and smelled rich/gas. I'm ordering the reman Bosch 3s from South Bay this week along with a gasket kit and fuel pressure regulator diaphragm.