Mostmint Racing

I recently got an 89 Vette from someone who had just rebuilt the engine and went to turn it on and was unable to because they has lost the original key. I started guessing and checking all 15 possible combinations of the VATS resistances with a variable resistor. When I tried 1-5 I got the security light and when I turned the key the starter cranked and nothing happened. On #6 there was no security light and when I turned the key it fired for half a second before cranking again. I went to troubleshoot and there's still no pulse to the injectors and no fuel pressure in the injector rails. There's fuel pressure where the lines connect to the lines going into the engine, but not on the nozzle where you can plug in the fuel pressure gauge.
Any ideas?

TheBlaster9001

I'd start by checking that there is 12v at the pump - if the pump isn't getting power, then you won't have fuel pressure. If the pump does have power, then the pump itself may be shot.
I assume that when you say there is pressure at the lines that connect at the engine that you mean fuel will drip out? Or does it spray out, like its under pressure? If it sprays out, then you know the pump is working, but pressure isn't reaching the fuel rails - which means the fuel pressure regulator is not working correctly.

So to summarize:
Check that pump has power
Verify if there is pressure before the fuel rails
Verify that there is no pressure at the fuel rail nozzle

I believe that the VATs module will disable injector pulses if the key is wrong or not present. Perhaps another resistance will get the injectors going again. But I'd first diagnose the apparent lack of fuel pressure, as it may be a mechanical issue.

aklim

If there is a starting issue, the first thing people blame, out of ignorance, is the VATS system. If you are getting cranks, I don't know how it is VATS. I don't believe we need to defeat VATS.

VATS will not allow you to start for 10 minutes, IIRC, after a failed VATS attempt. So when I tape the resistor and crank, it failed. You cannot do anything for 10 minutes or so. Go smoke a cigarette and come back. When you turn the key to run, does it pressurize the rails? It should. After that prime, I don't think the fuel pump runs till it has ignited? Not entirely sure on that one since I haven't done it for a while.

What I don't understand is how you say it has fuel pressure in the rails but not at the schrader valve. IF there is no pressure there, you either ran it all out cranking or your FPR is FUBAR and bleeding it somewhere. Have you tested it for leaks in the fuel system? What pressure? How did you ascertain it isn't getting injector pulses?

TheBlaster9001

Fwiw, my data logging software shows the pump come on to prime, then again once the ignition is bumped forward for cranking, and stays on until key off. I believe that this is the stock ECM commands as well, as seen when I was diagnosing a bad pump on gf's 86.

aklim

Makes sense. It primes when you put the key to run. Does it need a certain RPM or any RPM will work when it comes to turning the pump on? Maybe his FPR is shot and bleeding the fuel out before it has a chance to run?

Still, he should be getting pulses while cranking.

TheBlaster9001

Whatever the 'run' parameter is set to keeps the pump going, I think I set mine to 250 RPM. So as long as the RPM is above 250 (which will include cranking speeds), the pump is running. The ECM then checks every .1 seconds to see if the RPM is still above 250. I assume the stock ECM works the same way, with a flag parameter for 'engine on'.

If I understand what he is saying, then I think his FPR is shot. Assuming the pump works, and there is pressure at the filter/before the FPR, there should be pressure at the schrader. If there isn't, the FPR is likely clogged, bleeding, or stuck in some manner that causes all fuel to divert away from the rails.

It would be useful to know how injector pulse was determined, could it be they were working, and the lack of pressure is why it didn't start?

aklim

Makes sense. Didn't know what it was set for.

Exactly why I am curious how he said it was pressurizing but no fuel.

Agreed. Hopefully he used a noid light and NOT a DVOM

Mostmint Racing

The guy that had it before me bypassed the starter wire so it cranks no matter what the key. If the vats system was not satisfied with my resistance would it not power the FPR? If the FPR gets power regardless of vats then I think I'm looking at two separate problems.

I checked the pulses on the injectors by pulling an injector wire and hooking a multimeter up to the plug and got no voltage while trying the #6 code which supplied no security light.

TheBlaster9001

FPR is a mechanical system - not powered by the ECM, not electrical. Its the silver dome-shaped guy in front of the distributor. The fuel pump on the other hand is electrical - and worth making sure it works.

aklim

What is the FPR? Fuel Pressure Regulator or Fuel Pump Relay? Most here call the regulator FPR. If you are talking about the relay, I'd have to check since I believe it will fire up the pump with the VATS approval or not Won't bet either way. I believe it will pressurize the rail either way but not 100% sure. Get a gauge first and we can see if it primes and bleeds off the fuel or we might be able to go to the pump.

Repeat the test with a noid light since the pulses are about a millisecond long. Dvom might not catch it

TheBlaster9001

On the gf's 86, the fuel pump will not prime without VATs 'ok-ing' it. The only way to turn on the pump is through the relay, and the relay will only energize the pump if VATs doesn't throw a fit. My 85's fuel pump disable circuit works the same way, when the alarm is triggered the pump can not come on at all.

I think your best bet is to start by testing voltage at the pump - its easy to do, maybe 15 minute job. I can do a mini-writeup if you'd like.
Next, check what happens when you key-on. Does it prime, with 12 volts at the pump? When you crank, does the pump get 12 volts? If it does get 12 volts, the pump is bad. If not, something 'upwind' of the relay is not working right (could also be the relay itself).

aklim

OK. I'll have to test that. I know for sure that the injectors will not fire and it won't crank. Car isn't here so I can't test it.

Probably have to be real careful not to tear that boot. Ask me how I know.

Mostmint Racing

Ok so update. The fuel filter was the original factory filter. Has now been replaced. The fuel regulator was rusted to crap and it has also been replaced (taking great care to torque evenly to not rip the boot) and there's not some pressure in the fuel rails. But not enough to fire the injectors (which I used a light on. Thanks for that suggestion whoever said that. The multimeter didn't pick up the pulses as you said it wouldn't.) I'm troubleshooting the fuel pump next. So everything that could possibly be wrong, was wrong. Thanks guys

TheBlaster9001

At least it won't break down the road! Good progress. If the fuel system was that deteriorated up front, then replacing the pump and sock might not be a bad idea as preventative maintaince.

aklim

What boot? Is THIS what you are referring to? If so that is the diaphragm.

Translation? Are you saying there is no pressure or some pressure?

Injectors will fire regardless of the pressure. It will fire even when there is no fuel. As long as there is a pulse, it fires. It is that simple. If you are saying there isn't enough pressure and volume for ignition to occur, we need to go another direction. I understand you are saying that you got pulsing? If so that clears the ECM sending signals.

Does the circuit hold pressure? You need to ascertain. ASSUMING the fuel pressure regulator works, is there not enough pressure because the pump is failing or because the fuel circuit is leaking? Did you clamp off the return line, set the key to run and watch the fuel pressure gauge go up? With the new fuel pressure regulator, it should hold. If it doesn't, I would clamp off the return line and repeat test. If it won't get up to pressure, you may have a leak either in the injectors or the pulsator or you don't have enough pump pressure.

Mostmint

Just noticed I never followed up on this. Thanks again for the help.

1) the boot was the diaphragm yes.
2) we used a rheostat to learn the right resistance level so that was not the issue
3) there were multiple issues with the fuel supply - water in the gas, rust in the lines and injectors - it was messy. Bought a reconditioned set of injectors and spend a lot of time cleaning fuel lines and the gas tank.

Then we found no compression in one cylinder and low in several others - but that is a different story which I cover in my build thread.

Once got it running we did get a VATS bypass module which works well. That was mostly for reduced weight and complexity.