canoeman

Guys, Looking for the next step here. I ohm'd the original injectors and found I had 3 bad ones, also had zero pressure overnight. OK, it must be from the injectors being bad, (bad is 2 at 4.5 ohms and 1 at 14 ohms, when they should be 16.3). So the injectors have been changed but I still have a problem with hard starts. Did some research on here and found that the fuel pump should run for 2 sec. with the key in on, mine does not. Also these are new relays behind the battery that control it. So next step is to run 12v to G under the dash to turn the pump on all the time. Well as soon as I put the 12v to it the pump started and pressure was at 40lbs. The car started better, but the pressure started to drop to about 35lbs, I did not have the 12v going to the pump when I tried to start, didn't think it was needed. So now the pressure is 40lbs running and starts to drop after 30 minutes to an hour. 1. Is something wrong with the relay that turns the fuel pump on when key is turned (pump is new)? 2. What should I be looking at for the pressure leak, fuel pressure regulator? Any help would be great.

Da Mail Man

^^^^^^^^^^^^^^^^^^^^^^^

Guys, Looking for the next step here. I ohm'd the original injectors and found I had 3 bad ones, also had zero pressure overnight.
***pressure will not hold overnight and wil start dropping after about 20min - 30min..

OK, it must be from the injectors being bad, (bad is 2 at 4.5 ohms and 1 at 14 ohms, when they should be 16.3). So the injectors have been changed but I still have a problem with hard starts.
***welcome to my world and my 88.

Did some research on here and found that the fuel pump should run for 2 sec. with the key in on, mine does not.
***put on fuel pressure tester and observe while turning key "on"...the gauge should indicate the pressure increase.

Also these are new relays behind the battery that control it.
***corrected yes, one is the maf burn off relay and the other is a maf relay (on my 88). the fuel pump relay is to the passenger side of the brake booster.
So next step is to run 12v to G under the dash to turn the pump on all the time. Well as soon as I put the 12v to it the pump started and pressure was at 40lbs.
***that indicates that at least your fp is working and your pressure appears to be good.

The car started better, but the pressure started to drop to about 35lbs, ***will drop a bit when car is running...normal
I did not have the 12v going to the pump when I tried to start, didn't think it was needed. So now the pressure is 40lbs running and starts to drop after 30 minutes to an hour.
***see my above reference to this..

1. Is something wrong with the relay that turns the fuel pump on when key is turned (pump is new)?
***appears to be....the relay is approx $13 at advance or pepboys and is interchageable with the maf relay....always good to have a spare!

2. What should I be looking at for the pressure leak, fuel pressure regulator? Any help would be great.
***see above statements

edit; hooked on vettes caugh my error...good save.

Hooked on Vettes

The Fuel Pump relay is on the right side (passengerside) of the power brake booster and mounted on the firewall. The two relays behind the battery are the MAF Power and MAF Burnoff relay.

When you turn the key to RUN and the Fuel Pump doesn't run for 2 seconds, check the Fuel Pump relay wiring and relay socket contacts for burn marks. If everything looks good, replace the relay.

There are two sources that can provide 12 volts for the
Fuel Pump. The oil pressure switch and the Fuel Pump relay.

From your description it sounds like the Fuel Pump is running from the Oil Pressure switch (contacts close when oil pressure reaches 3 psi).

That could be why you're having long crank time before the engine starts.

Da Mail Man

...good save...caught my error on fp relay location!

pcolt94

Hooked on Vettes does have accurate information on starting, but just want to add some info.

When you ohm out an injector, and the resistance is low, that is an indication that the solenoid coil has low resistance. It might cause the injector to not spray properly due to the magnetic properties of the coil causing the valve to malfunction. But the low resistance is not a direct indication that the injector is leaking. For that matter, an injector with proper resistance can leak and not seal under pressure.

Other places to look for a pressure problem is the fuel pressure regulator, or the check valve in the fuel pump. I don’t know if there is a spec on how long the pressure will hold, but I don’t think I would be concerned unless it was 0 or something very low.

Da Mail Man

......."When you ohm out an injector, and the resistance is low, that is an indication that the solenoid coil has low resistance. It might cause the injector to not spray properly due to the magnetic properties of the coil causing the valve to malfunction. But the low resistance is not a direct indication that the injector is leaking. For that matter, an injector with proper resistance can leak and not seal under pressure."


...

AGENT 86

http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
http://members.shaw.ca/corvette86/Fu...l%20System.pdf
http://members.shaw.ca/corvette86/Co...20View%2086.pd

Sam Lam

Bill: Your post indicates you have a problem with hard starts. Please be aware that your 89 has a "quirk" programmed into the ECM in that the crankshaft must rotate two full turns before the injectors will fire. Can this be part of the problem that you describe? My 89 "had" this quirk until a friend modified the chip in my 89 computer and removed the two revolutions logic. There was another weird logic programmed into my 89 ECM. At 3600 RPM, the timing was advanced +12 degrees until 4500 RPM where it was removed I do not know why this was there either! Life goes on

RRT vette

A quick way to find out if the relay is bad is to, get a short jumper wire. Disconnect the fuel pump relay (shown in pic below) and insert one end of the jumper wire in the first terminal of the fuel pump relay connector and the other end of the wire in the last terminal of the connector. This is bypassing the fuel pump relay and if it is bad, you will get fuel pressure. If not, then you need to start checking wires and insulation at the fuel pump relay connector. You will need a factory service manual for this.

When the key is turned "on", the ECM sends signal for the fuel pump relay to close, sending battery voltage to the fuel pump, but for only 2 seconds (as long as the fuel pump fuse is good). You can usually hear the fuel pump relay open with a click after 2 seconds. You can also hear the fuel pump prime for 2 seconds. The fuel pressure should reach ~40 psi and when the fuel pump relay opens, the pressure will drop a few psi and hold. This gives the fuel rail enough fuel to start the engine.

There is a oil pressure switch located on the top rear of the engine next to the distrubitor that is the backup for the fuel pump relay. After you start cranking and the oil pressure reaches 4 psi, the oil pressure switch will close and send voltage to the fuel pump. In the case that the fuel pump relay is bad, you will get no priming fuel psi with the key "on". Start cranking and when the oil pressure switch closes, it will power the fuel pump. This can result in longer starts than usual.

The fuel system has a fuel feed line and a fuel return line. Once you shut the engine off, the fuel pressure should hold for the first 5 or so minutes. Then you will notice it start to slowly drop and return to the fuel tank via the return line. If the fuel pressure drops fairly quickly, then you have a leak in the fuel system and will have to use several procedures to locate the location of the leak. Hope some of this helps find the problem.

Da Mail Man

......does the same anomalie exist in the 88's?

Sam Lam

To the best of my knowledge...NO. Gbody5 was the person who modified the chip in my 89. He has an 88 convertable and his car did not have the two rev anomalie.

canoeman

I now need to start looking at wiring. I replaced the Fuel Pump relay last night 12 bucks no biggie, and that did not solve the problem. If I run 12v to G on the alcl I can hear the pump running. If I try to start the car in this jumped state it starts right up. If I just jump it to get the 40lbs and remove the jumper it still has the same issue with starting, though a bit quicker. I can see that when I try to start without the 12v to G the pressure drops to about 34 and take 5 seconds to start.

Hooked and Agent have been very helpful with suggestions and schematics. Just time to dig in a look around. My back loves all the leaning over.

Oh the pressure will remain at 40lbs for about 15 minutes then very slowly drops, so I know all is good there. After about 5hours of sitting it is down to 20lbs.

I'll update when I have more info.

Update after trials.

RRT vette

Did you try the jumper wire suggestion?

canoeman

On the fuel pump relay? No, won't be home for 4 more hours.

GreyHairedTopGun

If you have pressure when you apply voltage, but it bleeds off slowly over 30 or more minutes, than it is not the fuel pump.

I replaced my fuel pump last month because I had pressure when voltage was applied, but the instant the voltage was disconnected, the pressure dropped down to next to nothing in a matter of seconds.

It could be faulty wiring that is causing the fuel pump not to pump with the key. But the fact that it pumps (and holds) when you apply the 12 volts tells me it is not the pump itself.

RRT vette

It's either the fuel pump relay (new doesn't always mean it works), the fuel pump relay connector, the wires at the connector, or wires going from the connector to there respective places.

Fuel pump relay connector:

A... (ckt 120) red wire- fuel pump signal from ECM.
B... (ckt 450) black with white stripe wire- ground.
C... (ckt 465) dark green with white stripe wire- 12v relay drive.
D... (ckt 490) red wire- terminal G on the ALDL.
E... orange wire- connects to the 12v tower (fusible links) behind the battery

rick lambert

Said he did!

Since your pump runs when you do the jumper wire it means you have a problem in the wiring circuit! HERE is my question, when you say the wires to the fuel pump relay looked OK, did you pull the base of the relay away from the firewall and inspect the back side? At least in my case (and a few others) we've found the insulation on the wires shrinks back, exposing bare wires...mine were actually touching others.

One more thing.....even if everything is good you won't hear the fuel pump prime everytime, as in if you turn the key on it will prime, but if you turn it off and back on in a few seconds it won't prime again for 10-15 seconds.

canoeman

If the wires were shorting, wouldn't there be a blown fuse somewhere having to do with the fuel pump? All the fuses are fine, I checked them last night.

I have a fuel pressure gauge hooked up all the time trying to find the problem.

RRT vette

Even though you don't have a code 54. Follow the troubleshooting tree provided by AGENT 86, in the link below. It tells you step by step how to test the fuel pump relay circuts. Check that fusible link.

http://members.shaw.ca/corvette86/Code%2054.pdf

JAKE

I timed the fuel pressure drop on my 86 a few years back. Here's what I saw:

Beginning pressure 49 psi (immediately on engine shut down)
After 8 minutes 46 psi
After 1 more minute 43 psi
After 2 more minutes 40 psi
(9 psi in 11 minutes)
After 1 more minute 36 psi
After 1 more minute 33 psi
After 1 more minute 29 psi
After 4 more minutes 27 psi
After 2 more minutes 24 psi
After 4 more minutes 16 psi

At this point I got tired of watching the pressure gauge and my watch and called it a day.

So in 24 minutes pressure dropped from 49 psi to 16 psi.

No leaking injector and engine started and ran normally.

Hope this helps.

Jake