My car is in sig...

Been having problems with the stock 305TPI. Shut off on me while driving. Called tow truck. Restarted after about 10 minutes, drove maybe another mile, then shut off again. Decided to wait for tow this time. During the wait, I was able to push in the schrader valve on the fuel rail and there was pressure. It would crank no problem, just wouldn't fire up, nothing.
I thought it was maybe ignition module and coil at this point. This was 2 months ago... In the interim, back at my garage, the engine would fire up but run extremely rough, like it had some radical cam but would die as soon as I stopped pumping the gas pedal (remember this is TPI, no carb). Smelled rich too.

So I replaced the coil and module with AC Delco parts last week. Runs the same, no change. This time I pushed in the schrader valve on the fuel rail and no pressure. WTF?! I thought.

I'm going to put on the fuel pressure gauge this weekend, but some questions for you all as I've never had this problem before. And I'm in the middle of a 383 build so anything that needs further fixing, this build will take priority as far as parts needed. Already wasted money on the OEM coil & module.

1) Why is the oil pressure switch wired in parallel with the fuel pump relay?
2) Can these TPI engines actually run at all when the fuel pump is not working? And why would it smell rich when it I do keep it running?

Thanks all!

 

The oil pressure switch is simply a backup for the ECM/relay arrangement. Some misinformation on the web identifies it as a safety shut off in case of loss of oil pressure. It is not.

 

With the fuel pump not working , no , these engines will not run .

Now , what you've most likely got , is a fuel system that for whatever reason isn't building proper fuel pressure . Could be the pump , could be the electric supply to the pump is compromised (pump only getting 8 or 9 instead of 12 volts) , could be the rubber line connecting the pump to the rest of the sending unit (in tank , of course) has has deteriorated and began leaking , could even be the fuel pressure regulator . There are tests that can determine which component is causing the lack of proper fuel pressure and you'll have to do that troubleshooting to determine which component is at fault .

PS , as to the rich running ;

Our engines use the electric signal from the ECM to open the injectors and they use the fuel pressure to close the injector when the ECM removes the spray signal . In an engine with proper fuel pressure the injectors slam shut the instant the spray signal is removed from them . But , in an engine with weak , almost non existent fuel pressure , the injectors will continue to dribble fuel for some time after the spray signal is removed resulting in the abnormally rich running . I know it sounds illogical , low fuel pressure = a rich running condition , but knowing how the injectors work WRT how the fuel pressure closes them it makes perfect sense that the low pressure can't instantly close the injector as the proper pressure would .

 

Thanks for clearing that up. Sorta screwy engineering compared to present day designs...

Makes perfect sense the way you explained it!
I've replaced the fuel pressure regulator diaphragm right after I first got the car back in 2013. The ruptured diaphragm was pouring fuel right into the cylinders before cranking, resulting in hydrolock condition. Customer sold it to me for $500. Anyway, it looks like I'm needing a fuel pump now and a tow to work. Will confirm tomorrow with fuel pressure readings.

Walbro fuel pumps seem popular, as it will be feeding a 383 in the future...
Also, I'm not dropping the rear axle to get to this thing. I'll probably carve an access door like some have already done here on this forum.

 

I'd never cut my car up for a fuel pump... The rear is the easy part. The b%$#h is the exhaust if you plan on reusing it! Rear doesn't need to come completely out. Unbolt the driveshaft, torque arm, and panhard bar and it will swing down far enough to get the tank out. If you have the car high enough off the ground...

 

Just do it right. Barring extremely fusty fasteners, it's not nearly as difficult as people make it out to be. To get the sending unit out through an access hole, the fuel lines have to be cut, and the thing has to be fished out... Hardest part of dropping the tank is getting the muffler out of the way. Not sure how that is in anyway more difficult than cutting a huge hole in the floor.

 

I thought the oil pressure/fuel pump was for accidents so the pump didn't keep running when the engine was stalled?

Regardless, I found a strange issue a while ago. I was priming the oil pump/system after a valve spring swap but didn't have the fuel rails and injectors installed yet. Apparently I had left the battery connected. When the oil pump reached prime and started to make pressure the fuel pump started up and fuel sprayed out of the disconnected hoses. This is with the ignition off. I didn't know what it was at first and it was puzzling. I figured it out after a minute of thought but it's a good reminder of why to disconnect the battery when doing any serious work. I would have never thought that would happen with the key off but it did.

The issue of whether to drop the fuel tank for a pump swap is a personal choice and I don't think either way is right or wrong. I just had my tank out a while back for different reasons but I can't see how it would have come out with the rear axle in place. I had mine out along with the exhaust and even the panhard mount brace. It was still a twisting puzzle to get it out even with everything removed.

 

Now that is truly interesting and proves real schematics don't lie!

Had a chance to test my issue and attached a fuel pressure tester onto the fuel rail. Turned the key and saw pressure shoot to 40psi then quickly decine... Running, fuel pressure was hovering around 40psi too but once again running rough as hell and rich. I think I have a bad return hose in the tank. Ugh. Prolly thanks to this 10% ethanol additive 'round these parts.

 

40 PSI running with vacuum connected may be a little high but I wouldn't necessarily suspect the fuel return. IF the return was clogged causing the engine to run rich the I would expect the pressure would be elevated more. 40PSI running seem to be about right.

You can remove the vacuum line at the fuel regulator to see what the max pressure is running. Then, put a vacuum gauge on the intake manifold when running at idle. record these values. The regulator will reduce fuel pressure by the same amount as the manifold vacuum. Without going into all of the conversions just take the manifold vacuum and divide it by 28, then multiply that value by 15. This will give you the amount of change in fuel pressure to expect, vacuum connected vs disconnected. For example;

47PSI (MAX fuel pressure with regulator vacuum hose disconnected)
20"/hg (manifold vacuum at idle)

20/28=.7143*15=10.7

47(PSI max vacuum disconnected)-10.7=36.3PSI running with vacuum connected.

You need to plug in your actual values but you get the idea. If the fuel pressure is varying by the expected amount I would look to other issues.

One reason your idle pressure may be high is because the engine is not running properly, and therefore isn't making as much manifold vacuum at idle, and therefore not reducing the running fuel pressure as much as it would if the engine was running properly. It may actually show you that the regulator/return system is doing just what it is designed to do.

 

Thanks for the help... But I'm starting to think I might have 1 or more stuck injectors due to the quick loss of pressure, or maybe a torn diaphragm in the fuel pressure regulator. I'll report back when I finally figure it out.

 

The fuel pump has a check valve built into the outlet. If the check valve isn't doing its thing, you'll lose pressure at the rails as soon as the pump shuts off. Had it happen when a fuel pump was damaged by a rear ender. Car was hard to start, and would die after running for a short time. Would start up after sitting a few minutes. New fuel pump, all was good again.

 

Ok before I bite the bullet for a fuel pump I noticed what I thought was odd behavior on the fuel pressure gauge while cranking. Actually my son was cranking, I was observing the fuel pressure. Whenever I opened the throttle, the fuel pressure would suddenly increase. Is this normal? Or is it pointing to a bad fuel pressure regulator? I disconnected the vacuum to it and no fuel comes out.

 

You dont need to do all this.

Unbolt the sway bar, panhard bar and shocks then the rear will just drop. The driveshaft, torque arm can stay bolted.

Its honestly not as hard as it seems. Trust me i made a huge deal out of it and was able to knock it out one day with hand tools and floor jack.

 

Probably normal, the intake manifold pressure also increases when you opened the throttle.

RBob.

 

RBob, thanks it actually makes sense to me too, but one doesn't normally see this stuff until sh*t like this happens.

I'm gonna try one last thing, a new Optima AGM battery, 750Amps. I've been jumping this engine (plus a dead *new* battery datecode 1/17) with one of these. Maybe voltage wasn't getting to where it needed to be... This problem did show up after it sat for over a month and it just doesn't jive with the initial symptom of sudden shut off while driving.

Installing now, fingers crossed!

 

Same erratic firing with engine barely running with foot off throttle and me under the hood without son this time maintaining throttle...

This time I noticed a bad oil leak towards the front of the engine, so I checked the oil level. It was about 2 inches above the hash mark and smelled of fuel.
During this latest testing, I was able to unplug the right side injectors, one at a time while keeping it running. I'll have to save the left bank till tomorrow. It's misfiring so bad, unplugging each injector resulted in no change of behavior. Fuel pressure was at a steady 40PSI while running, despite the leakdown when pump was off. So I don't think the pump is the issue at this point.

So now it is definately either stuck open injector(s) AND/OR a torn fuel pressure regulator diaphragm since fuel is getting into the oil pan.

 

Got a scanner? What does the ECM think engine temp is?

 

I don't know, but I follow your train of thought.

Finally got around to disconnnecting the cold start injector and the rest of the injectors, one by one, on the drivers side. Still ran rough as hell. Now the oil was pouring out of the front somewhere...

Done with this engine. It is a sign. I must push forward with the 383 build now.

EDIT: Also, when I get this 305TPI engine out, I'll be willing to part it out somehow. Probably whole assemblies, like intake/TB and block with heads