Hey Everyone, sorry if there's already another thread with a similar topic. I searched for awhile and couldn't find anything. I'm by no means an expert mechanic, so forgive any improper wording or terminology here please!


I've got an 84 Z28, with rebuilt blueprint BP355 motor with a Fitech Go Street EFI system. For the past year I've been experiencing a weird issue. I'll use yesterday as an example to illustrate the problem:


I took it out for a drive yesterday afternoon. I live in UT, so it was a high altitude mountain drive. I was able to drive for about 1 hour with ZERO issues. No misfires, no hesitations, no overheating, up steep mountain passes at 70 mph for extended periods of time. However, at around the 1 hour mark, seemingly out of nowhere I started losing engine power. At first it was hard to keep it at 70 mph, then 60, then 45 etc. It felt like the motor was slowly choking to death, the more I pushed the gas pedal, the faster it lost power. This happened over the course of about 30 seconds. Eventually it sputtered and died altogether, and I had to pull off to the side of the road. If I tried to restart it, the engine would crank, catch, and immediately sputter and die, no matter how much gas I gave it. I waited about 15 minutes, and tried again. This time it fired right up, so I got back on the highway. It ran great for about 10 more minutes, at which point it repeated the exact same process. This time I left it sitting for about an hour before starting it. Started right up, and was able to drive for about 30 minutes this time before it died. I continued this process for the next several hours, making my way home 5 miles at a time.


Like I said I've been having this issue for the past year now, and have tried lots of things to fix it. Here's my running list of what I've tried, in chronological order:


replaced plugs/wires

replaced distributor (including ICM, cap and rotor)

had a professional rewire my entire fuel/ignition system (did fix an rpm noise issue i was having, but didn't solve this problem)

cleaned out fuel lines/replaced fuel filters

replaced header bolts/gasket, intake bolts/gasket, egr bolts/gasket, and exhaust collector bolts (wanted to rule out exhaust pressure issues)

New radiator, thermostat, engine fans, and air dam (operates at about 200 degrees now, never gets over 215)

replaced FiTech in line fuel pump and filter with an equivalent Bosch fuel pump/filter (When I called FiTech, they told me the issue was most likely fuel pressure related, so rather than sending my fuel pump into them to repair, I just bought a new pump)


With my limited mechanical knowledge i'm running out of ideas here. The only other things I can think of are:


1. air intake - Currently the car has no cold air intake, just an air box that sits on top of the EFI system in the engine compartment. So maybe the hotter the engine compartment gets, the hotter the air is that's coming into the EFI, which eventually chokes it out?? Do you guys think purchasing a cold air intake might help? Or maybe just punching a hole in my hood, and installing a scoop?


2. vapor lock? I read something somewhere about fuel lines getting too hot and vapor locking. But I also read that that's extremely rare with an EFI system, so I dunno. I do have an inline fuel filter that sits right next to the EFI unit on top of my intake. Could it be possible that this plastic duralast filter is causing issues?


Not sure if either of these things are realistic guesses, so I thought i'd turn to the legendary Thirdgen forums for guidance.


Thanks all!

 

Feels fuel related to me.

What was the fuel pressure while it was screwing up? What happened when you shot starting fluid in it?

 

Haven't checked pressure. Not sure how i'd check that while i'm on the side of the road (super limited in my mechanical knowledge here). I'll try starting fluid for sure though. I'll bring a can of fluid out with me next time i'm on the road with it.

 

I have heard on here that guys were reporting troubles with gas getting too hot and causing pumps to fail or something

never experienced that but i only ever drove for 1-1.5 hrs at a time before and it wasnt hot out

sounds fuel related with heat. What is the fuel pressure set to? Anyway to log it and see what happens if you can repeat this drive?
Lsx stuff is set to 58 psi base to help fuel boiling/vapor lock issues since they dead head the fuel to the rails. Could try setting fuel pressure much higher and retuning for that

 

Have you checked to see if pressure or vacuum is building up in the fuel tank when this occurs?

GD

 

How would I go about checking that?

 

By hooking it up and driving around with it duct-taped to the windshield.

Not a very "mechanical" kind of thing at all really. More a matter of, letting your WILL beat your CAN'T.

But that's not even all that necessary. THIMK: temporarily permanently install your fuel pressure gauge improperly, such as, on your back seat floorboard; when the car fails and won't start, install it temporarily properly (hook it up); observe it while your assistant attempts to start it.

 

Are you using an external electric fuel pump? They are notorious for failing either intermittently or altogether and no OEM uses them. An in-tank pump will be cooled by the fuel. Most external pumps will fail at 1 year or less, sometimes multiple times, before their owners give up and go to an in-tank setup.

 

Unscrew the fuel cap - if you get a big WHOOOOOSH!! of air (either in or out) and then the car starts up normally..... you have a pressure or vacuum build-up in the fuel tank. Pressure can come from a blocked vent line or malfunctioning vent valve. Vacuum can come from the engine if the purge solenoid were to fail open, etc.

GD

 

Before jumping to conclusions and trying to troubleshoot details, I'd suggest locating the issue to the correct SYSTEM of the car FIRST.

Won't do A DAMN BIT OF GOOD to futz with the gas tank or get worried about the fuel pump if the problem is in the ignition. Not any more than it would to dink with the distributor if the problem is fuel.

Logic. Reason. Orderly thinking. Rationality. Cause and effect. Not, "maybe it's this maybe it's that". Just because a bunch of us out here says "it sounds like fuel" doesn't mean it's already time to start tearing the fuel system apart. Instead, it's time to clearly and definitively LOCATE THE PROBLEM, and once it's been isolated to some particular function, THEN AND ONLY THEN tear into THAT function. Not just mindlessly mess with the car.

 

^ Exactly, fully diagnose, then move forward.

Saying "it's fuel" gives you a starting point, but not a definitive.