Hey Guys - Could use some help diagnosing. Here is what I've done so far and the related test results: BTW - Fuel pump is about 3 years old.

1. New Distributor Cap and rotor
2. New fuel filter
3. No Engine light, no diagnostic codes to report when scanned


Measure Fuel Pressure:

This is where it is a bit strange, not sure if it is my gauge fittings have a small leak that I can't detect. But here goes...

1. Engine cold not running - Pumps up to 45 PSI like a champ. Won't hold pressure. Each time I turn key, back up to 45 PSI no problem.
2. Engine cold - Starts like a champ with one key turn.
3. Engine running - fuel pressure holds about 43-40 PSI. Seems good.
4. Engine temp starts to climb - Fuel pressure starts to climb.
5. Fuel pressure gets to about 50-52 PSI, engine stalls.
6. Engine warm and off. NOW, pressure holds. (this is why I suspect gauge fittings need warmed up)
7. Bleed off fuel pressure to zero
8. Turn ignition key on, but don't start engine. Pressure only gets to about 30 PSI.
9. Can't start engine from this point on - (it will start, but not stay running, fuel pressure too low, won't get back up to 40 PSI)

10. At this point, manual call to apply vacuum to Fuel Pressure Regulator to see if it responds, I don't have a way to do that at present time. I did check vacuum lines for clogging and they seem OK.

11. With ignition OFF Applied 12 Volts to fuel pump relay harness terminal A and pinched fuel return hose. Fuel pressure shot to the sky.

If I let engine cool back down, it will start again. Its almost as if the Ignition Coil or Ignition Control Module are bad and once they heat up they crap out (from what I've read on other TGO experiences )

Next set of tests:

Ohm Tested Ignition Coil. (thanks for photo Tuned Performance)

Test 1 - Infinite
Test 2 - The meter hunts and can't find a measurement, but meter seems to hunt in low Ohms range**** Is this OK ???
Test 3 - 7.9 ohms

Photo of test is over here:
https://www.thirdgen.org/forums/tech...ml#post6209017


Ohm tested Distributor Pick up coil : checks out good

Could be a leaky injector, check valve in the pump, or bad regulator causing the pressure bleed off. Depending on your brand of pump even 3 years old it could be going bad.

Could be exhaust too close to fuel line (or other heat source) and you are getting vapor lock.

During the no start situation are you getting spark?

Remember these car's fuel system was designed before ethanol was in fuel. Go to puregas.org and see if you can fine ethanol free gas in your area and use that if you don't drive the car all the time.

Go buy a cheap vacuum pump and test the regulator -- the ones that come with the parts store brake bleed kit should work.

-- the other thing when its cold and it will crank does it fire right off or do you spin the starter for a while? If you spin the starter for a while you may be building enough oil pressure to enable the fuel pump on that circuit, but with hot oil you can't (this isn't an issue with oil pressure just how it works). Put a multi meter or test light on the fuel pump relay and see if its running in the start position during the no start situation. If your pump isn't running in the start position until you build oil pressure then there is a wiring issue (or possibly the ECU/pickup/ICM).

Thanks for reply - Haven't done this yet. Will give it a shot. I'm thinking between steps 5 and 6 of fuel pressure measurement, bad injectors would not be the primary problem.

Something seems to be leaking when cold, (gauge, injectors, fuel lines, pump) As a side note, I have bought gauge from Amazon, the professional one I borrowed from Autozone visibly leaked gasoline! Test equipment may not be the best thing to borrow from them.

I need to block fuel return line and see if it holds when cold. But when warm, pressure holds. If bad pump or leaky injectors, it isn't happening when warmed up. I blocked fuel return line when warmed up and pressure sky rocketed. I forgot to do this when cold.

hmmmm

Didn't verify, but car will run, just rough before stalling, so there is at least some spark.

Definitely need to do this before tearing down the fuel system!

Fires right up when cold.

Good idea. Will rule this out.

My car would start cold, then after 10-15 min, not restart. 2 of the 8 injectors were bad. I replaced them all with a set f 22b injectors from FIC in GA.

I had a similar start/no start... was the O-Ring feeding the 9th injector leaking. Finally saw it when I had my son cycling the key for me while I was under the hood checking things... and there it was. Replaced it and no more fuel issues.

Do you SMELL gas?

When the pump primes you are seeing 40-43 psi which is correct however it rising to 50+ is not correct. Once the engine starts manifold vacuum is applied to the regulator and at idle you should see roughly a 10 psi drop. Immediately I suspect something like a regulator issue or return line restriction. Even with jacked injectors the psi shouldn't exceed the 40's. If it were me, I would tackle that issue first.

Definitely need to rule out fuel pressure regulator. Have cheap vacuum puller on way from Amazon. If it is the regulator, what would cause problem #8 of the fuel test? (cant get above 30 PSI after bleeding off pressure and everything is warm) I clamped down the fuel return line from the regulator and PSI shot up. That tells me pump is working, and is capable of giving the 45 PSI needed. Right? Is fuel pressure regulator a one way valve? Even if it fails?

If it is in fact the fuel pressure regulator then this is how it is functioning:

When cold it is stuck open and doesn't hold pressure, and when warm, it holds pressure, (was even holding 55 PSI), and after bringing pressure back to zero and re-priming, it would hold no more than 30 PSI.

So when you are seeing the warm 30psi, it is during the 2 sec key on pump prime correct? Then you clamp the return and it responds with 40+ correct? If yes to both I would definitely suspect the regulator. Clamping the return essentially dead heads the pump and should produce excessive pressure every time. The regulator isn't a one way valve and it is technically on the return line, this means the injectors come before the regulator on the pressure side and the regulator is providing a controlled "leak" that returns to the tank via the return line. When you clamp off the return line you plug this "leak" and will see max pump pressure on everything from the pump through the regulator. If you are building and holding pressure with the return clamped you can reasonably assume the injectors are not leaking and the pump is ok. You may be seeing an intermittent or heat sensitive regulator failure, usually you see it good or not but things can happen.

Well, it makes sense to some degree, but my concern is I can't really fully run an injector test when the system is cold. One where each injector is allowed to run by itself and fuel pressure drop is noted across each injector. So it would be a real drag to replace the fuel regulator and get everything put back together and find out there was also a leaky injector that is failing when cold. If injectors are not holding pressure, how fast will the system leak down pressure? When cold, I lose fuel pressure pretty quick.

You're losing pressure with the return clamped? If yes, then you could have a leaky injector or a leaky pump check valve (or line leak but you would probably see and/or smell that). To narrow it down you would prime the pump, clamp both feed and return lines which will isolate the injectors. If you still lose pressure you have narrowed it to the fuel rail/injector area. These are both tests you run with the engine off. You should be able to hold pressure for 15 min or better, it will bleed off slowly.

only losing pressure when cold. when warm, pressure holds excellent. I need to run your proposed tests in this reply when cold.

Will definitely do next time I get to the car. Been working most of the day!

BTW - Nice injector test over here: https://www.thirdgen.org/forums/tpi/...injectors.html

Still same issue, fires right up when cold. Can't start again. Getting totally different results this time on fuel pressure. Fuel pressure seems to be good now. Maybe the new gauge needed a little breaking in. Or things are just behaving different today.

Measured fuel injectors:

Injector #1 reads 2 ohms. After warming up (can't get hot) reads 6.7 ohms.
Injector #2 reads 15 ohms. After warmup reads 14 ohms

All other injectors read 15.7-16.2 and all increased in ohms after warmup, most about .1 more ohm, another .3 ohms more. Which makes me wonder why injector #2 decreased in ohms.

For as much work as it is, I'd replace all injectors, fuel reg, egr. did I miss anything? Plus I can store the factory stuff away in my mini museum A lot of people seem to talk Bosch and Southbay. I like to use GM parts when possible and not sure about going with rebuilt stuff?? Bosh is yellow, where factory injectors are blue. trying to keep factory. any thoughts on all that?

Are the Delphi's as good as the Bosch? Honestly, haven't studied injectors much, but brief reads of threads I've run across seem to point that the multecs suck and bosch run forever.

I would bet there is a clog in the fuel system. Hope you changed the fuel filter. Blow through the lines towards the engine with compressed air also.
The way you describe it sounds like the fuel sock is clogging though.
Notice it primes fine when cold- a sign the clog isn't there yet (hasn't been picked up).
Once you run the engine for a bit the fuel sock picks up a bunch of debris and clogs tight.
Thats when the pump struggles to hold pressure.

otherwise bad fuel pump. But I doubt it since they tend to just fail.
Also, not saying the injectors aren't bad. but you might be looking at two different issues.
The fact fuel pressure is changing/affected directly suggests the fuel pump/clog, and has nothing to do with injectors.

Try this. Try running the fuel system without the engine on. Find the fuel pump relay and turn it on manually. Or simply apply 12v to the fuel pump wires at the tank. Run it for a while and see if it clogs up.

The only strange thing is the rising pressure while engine warms. That indicates a regulator problem. So maybe you just have a faulty regulator.

Was looking at Delphi website, looks like they only make them for 5.7's, nothing for 5.0's. Southbay website seems to reflect this too. Do you think 1 bad injector could keep the car from starting?

Southbay will rebuild your originals if that is the route you take.You can ship them to them and they will also test not just the coil but the spray also. I have heard bosh 3 needs a new tune but to be honest my buddy put a set in his 305 and it runs fine with no retune, they do deliver a little more fuel. You want #19 pound injectors for a 305.

Bad coil yes, and you do have a bad coil reading on both 1 and 2. All your injectors should really be within 1 ohm max.of all 8. The ohm test will not tell you if a injector is leaking.

No experience with Delphi's, and I have heard the same about the Multec's but from my experience I have the original Multec injectors and all ohmn within .3 of each other, they are quiet, and car idles so smooth that if not for the exhaust you would think it stalled. The Bosch 3's om my buddy's car are loud IMHO.