Fuel pump or not?

Rogier · 01-06-06, 03:41 AM

Hi,

First to introduce myself:
My name: Rogier de Kreek and I live in the netherlands. My background consits of mechanical automotive engineering and nowadays I work as a manager in a caterpillar / mitsubishi forklift plant.

I just some weeks ago purchased a '89 corvette coupe. 6 speed manual gearbox with ride select option. (which is not functioning...) I had at that time the two options most people have to buy a corvette: 1. save money up untill I had enough to buy one that's completely ok or, 2. buy this one knowing that I have to do a lot about it to make it ok.

So first things first:
The car is (was) running. It didn't rev very easily to it's higher rev's. It appeared to be holding in. (felt like it didn't get enough fuel) Lower rev's were fine though.
Also it ran quit evenly. So no hickups or so. (excuse the spelling)
The car started only after starting it for 30-40 secs or longer.
Later it started even worse and it appeared that it would shut down during driving. Now it won't even start anymore.

At first I thought it was the ignition timing and that it would lower it's timing at higher (more vacuum) revs. So maybe some hosing's loose or so. But later when the other trouble's occured I figured that it must be the fuelpump. So at first not enough pressure and later no pressure at all. I also read out the ECM which said that the left oxigen sensor read lean mixture. (not enough fuel - helping me in my second opinion about the fuelpump) The engine check light lit up during the last drive at which it almost shut down during driving. So then the errorcode was written in the ECM. Making it still possible to be the ignition. (?)
I read some threads in which one guy stated that you can hear if the pump is faulty or not by turning the ignition and the listen at the tank. But I figured that when it does turn but put's out no pressure you might hear it but it's still faulty.
I also looked at the ignition for five seconds and then saw that the fuel pressure regulator hose for vacuum regulation was disconnected. This cannot cause the problem but the previous owner might have done that to increase fuel pressure at the injectors to balance the lower output from the (almost) faulty pump.

It's currently -5 degrees C. here in the netherlands and I have to work outside that's why I am first asking any opinions about this problem.

So anybody any Idea?

gmjunkie · 01-06-06, 04:26 AM

I would go with a Fuel Pump but I would check out Catalytic Converter Too!! Spark Plug's should be WET or Real Dark and Manifold Vacuum Low if cat is Plugged!!

junk!!

tigmaned · 01-06-06, 06:27 AM

do you hear the fuel pump kick on when you turn the key in the on postion? have you put a fuel pressure gage on schraider valve yet? yeah the last own removed the vacuum line to the FP-reg for more fuel psi? how many miles on your 89? maybe if the pressure is just low or some things in the filter?? yeah wish full thinking!! but the best part vette's are simple to change the fuel pump!! you can do it in a hour or two takeing your time! not sure if they ship way over there but i got the one for my 86 from rockauto.com for about $60 i think?

Rogier · 01-06-06, 06:44 AM

I did not check if I can hear the fuel pump kick in when the key is switched to "on". I will check this this weekend. Do you hear it easily or do you have to take the filler cap of or something like that?

I did not put a fuel pressure gauge on the schraider valve. Can you tell me exactly where it's located? I will look for a pressure gauge though.

It has done appr. 70k miles.

Corvette Central shippes over here that's good enough. 74 dollars or so.

I don't think that's the filter because that would make the car die out over a much longer period of time I think. Not that's dead completely in an hour or so. Same goes for the upper post with the cat conv. That would cause a problem but probably not in two cat's at the same time so the car would, difficult but, still be able to start.

tigmaned · 01-06-06, 07:40 AM

the scharider valve is right near the F/P reg, on the fuel rail on the right side of intake, it looks like a tire air valve. for my 86 i think fuel perssure should be 39psi, its in the GM service manual for sure. but i think all (85-90) L98 motors are the same?
when i turn my key in the on postion i hear little motor hum sound i guess you would call it from the pump.
once you get it started check under your vette and see if the cats are brite red in color, if they are you my need new ones?

G Winter · 01-06-06, 08:06 AM

It sounds like your vette may have been neglected,so you could have multiple problems. Be sure to check spark, the way you discribe things getting worse you could have a bad ignition module.

Glenn

77-85 · 01-06-06, 08:20 AM

I had a very simillar problem with my 85 Vette. In my case it turned out to be a faulty oil pressure switch. I am not sure if your 89 has the same wiring for the fuel pump, but in my 85 the fuel pump is powered by a switch controlled by oil pressure.

When you first turn the ingnition to the run position it operates the fuel pump relay which turns on the fuel pump (you can hear the pump run before you start the car).

Once the car has started, the fuel pump relay opens, and the power for the fuel pump comes from the oil pressure switch which is closed as long as Oil pressure is present.

The purpose of this circuit is to protect your engine incase you lose oil pressure. In my case, the oil pressure switch was opening intermitently and causing problems simillar to what you are describing.

The oil pressure switch is located directly behind the distributor. You will see two sensors, one is the oil pressure sending unit (for the dash), and the other is the oil pressure switch. The oil pressure switch for the fuel pump is the one with 2 wires.

The part itself is very inexpensive, but it is a bit of a pain to get to. I had to remove the distributor to get at it.

Rogier · 01-07-06, 10:09 AM

Okay, checked the fuelpump by putting the ignition key in the "on" position. It doesn't sound very confident. I hear a mildly prr-prr.. and then it's quiet. I expected a good fuelpump to do: wzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Or is it only shortly engaged when the key is in the on position?

LT4man · 01-07-06, 10:26 AM

The pump only works until the pressure builds up. Then it shuts off.

Save The Wave!

Rogier · 01-07-06, 10:30 AM

I understand... but what is normal? In seconds I mean. I had another car which I could hear the fuel pump run and it took that car about 5 seconds to build up complete pressure. I wonder if the 1 or at most 2 secs of this pump is enough. I guess I only know when I test the fuel pressure at the injectors or not?

LT4man · 01-07-06, 10:55 AM

Every car is different regarding the time the pump takes to build up pressure. You will need to attach a pressure guage to the fuel rail, turn key on, note fuel pump pressure reading on gauge.

Save The Wave!

gmjunkie · 01-07-06, 10:58 AM

Quote:

Originally Posted by Rogier

I understand... but what is normal? In seconds I mean. I had another car which I could hear the fuel pump run and it took that car about 5 seconds to build up complete pressure. I wonder if the 1 or at most 2 secs of this pump is enough. I guess I only know when I test the fuel pressure at the injectors or not?

Some Pump's Only need a second or two!! I'd check the Oil press sw as 77-85 suggested!! Egni.Mogul will act this way too!! and so will a ECM and it will usually won't Tell on it's Self, it will However Give you a code for something other than It!! Like EGR,TP sensor,Oxy sensor, MAF sensor, MAP sensor,Idle Solenoid, Or all of above!! But Almost always won't tell on it's self!! But I still wouldn't Rule Out a Cat Converter, Dose it Pop or Back Fire?? Dose it Blow back out of Throttle Body??

junk!!

Rogier · 01-07-06, 03:23 PM

No, it doesn't pop or back fire, it just dies out as it get's no fuel or a really bad distribution of sparks..

Is it possible to shortcircuit the oil pressure sensor? Is it an 100% open or 100% closed sensor? That way I might be able to fool the ECM and get the pump on it's way...

speedmaster4 · 01-07-06, 06:02 PM

ecm runs pump for "2" seconds if no distributor signal to indicate engine turning over...remove gas cap and put ear to opening while helper cylcles ign key

GM in -tank elec fuel pumps are good for 10 years or 100k miles, whichever is first (voice of experienceS)...if either--change the pump, and the short 'wiring harness' in the tank (many,many 'pump failures' are just corrosion at wiring harness connector)

new 'sock' filter too of course

Rogier · 01-09-06, 05:23 AM

Okay, thanks a lot. It al helps you know.

The temperature today dropped even lower so it's not only freezing now but it's freezing hard! I ordered the fuel pressure gauge at corvette central so I will be able to meassure the fuel pressure. At that time I will see the ignition as well and will be able to pinpoint the exact problem.