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Pump cavitation/ vapor lock


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Hey how's it going? 

 

Ive been dealing with my 77 280z turbo project these past few years and Im having a serious problem with either pump cavitation or vapor lock. I dont care what you call it, it's getting really annoying. The car will start up and drive just fine to my destination; however, if it sits more than 10 min I have to sit for several hours just to get the afr back to a safe driving range range. I only work 5 miles away and I usually have to wait my entire 8 hour shift for it to not be running super lean. Several times I have tried to leave and go on lunch but my AFR is at 17+ so I was stuck till it went down.

 

Ive tried heat shielding everything, tried different pumps (currently with a walbro 255), bigger fuel lines (only the rubber lines, not the hard lines), I have hood vents, Ill even leave my hood open half the time hoping that will help. My normal AFR at idle and cruising is about 13.3, but when this leaning out happens, it get to 15's+. While the car is on, the temp doesnt get above 180.

 

Im assuming its pump cavitation solely based on that Ive noticed my fuel pressure being lower whenever this happens (plus people have said that z's cant get vapor lock). Ive even revved the engine and watched the fuel pressure plummet the higher the RPM's get, plummet as is goes from 32 psi to 0, or pretty darn close. 

 

Any advice is extremely appreciated. If there are any questions about specs/parts/anything, please feel free to ask. 

Austin

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Is the pump in the stock location? How is your regulator plumbed? Either the fuel is boiling before the pump or in the rail. Is the exhaust near the pump or lines? Have you tried different types of fuel like ethanol free or maybe race gas or aviation fuel? I've notice mine is worse when i get fuel from quick trip or racetrack. They seem to add stuff to the fuel that lowers the boiling point.

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Ive been dealing with my 77 280z turbo project these past few years

 

 if it sits more than 10 min .....  Ive even revved the engine and watched the fuel pressure plummet the higher the RPM's get, plummet as is goes from 32 psi to 0, or pretty darn close. 

 

Ive tried heat shielding everything, tried different pumps (currently with a walbro 255), bigger fuel lines (only the rubber lines, not the hard lines), I have hood vents, Ill even leave my hood open half the time hoping that will help.

 

Im assuming its pump cavitation solely based on that Ive noticed my fuel pressure being lower whenever this happens

 

Reorganized some phrases.

 

Basically, your problem is that fuel pressure drops below the normal 26 - 36 psi range it should be in when off-boost.  Zero means that the pump isn't pumping, there's a blockage between the pump and pressure gauge, or that the FPR is stuck wide open.

 

Your assumption is probably off.  Cavitation and heat are not a direct correlation.  Vaporization is not cavitation.  "Vapor lock" does not cause cavitation.  Just saying, these are all relevant words, they just don't really fit what you're seeing.

 

Forget about heat and cavitation for a while and confirm the basics.  Pump power, supply to the pump inlet from the tank, etc.  If the problem lasts eight hours, that's plenty of time to get underneath and do some looking and measuring.  

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As asked is your pump mounted in the stock location? These pumps almost need to be mounted low enough to be gravity fed by the tank otherwise they will sooner or later start complaining. Do you have a filter between tank and pump? This can cause the pump to complain. One big thing that I've found through JeffP's posts and my own experiences is that using the stock wiring and stock relay is not advisable. Any aftermarket pump needs to be pretty much upgraded to bigger wiring. Using the stock wiring I was experiencing a very hot relay and a 1v drop from relay to pump once warm. Part of what I did was get one of those 70amp relays they use for the electric cooling fans and upgrade to 10 gauge wiring.

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I think I figured out the problem. As suggestedby NewZed, I believe my fuel pressure regulator was sticking open. I bought a different brand fpr, tested it out and havnt noticed any similar symptoms. Also Ive noticed that my car now keeps fuel pressure after I turn off the car, all the other fuel pressure regulators that Ive used dropped to 0 when I turned the car off.

 

I rewired my whole car to incorporate the megasquirt ecu, the pump is placed in the same spot as the stock one (maybe even a little lower), no exhaust near the lines. So Im going to keep monitoring the situation to make sure everything is still good.

 

However a new problem arose. I believe my alternator just took a dump. While I was driving the other day I watched the voltage on my dash gauge dropping slowly and my AFR slowly got leaner until the car died. I did the alternator upgrade a while ago but I either screwed that up or the new ecu, it's components and electric fans are using to much juice. Ive tested the battery when the car was on and it was only at 12.3v. I think that is a bit low (thats without lights, ac, blinkers, or radio). The alternator is O'Reilly brand 60amp. The electric fans are the Flex-a-lite low profile S blade 12in 420 (I know these things use a lot of juice), these are wired to the key's "on" position. 

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  • 2 months later...

Hi!

Crap, man, you described two things that happenned to me. I have an 1983 turbo-ed and megasquirted engine.

 

The low afr on restart, even after 2-3 hours, is STILL happenning, so i'll check into the regulator.... Eventually (money).

 

As for the electrical issue, my alt died on me (would not charge) so i got it checked (twice) and they eventually changed the internal regulator (its the stock 1983 with internal reg. I dont know if yours is the same... Then 2 days later i realised i was running on battery power when at low rpm( ask me how i know it didnt work at iddle: i was in traffic for 30 mins, and the voltage got so low the afr gauge stopped working and started blinking. Dindnt understand so i figure i' stop-restart the car to reset it.... Tic tic tic tic, on the highway, as traffic starts to move... Arg)

I took it to a different shop, and it turns out the tridiodes had died too. Been working fine since...

 

Your battery, when charged (after a drive) should not be below 12.7 volts. While the car is running, you should be around 14 or so.... If you charge the battery and it does not hold 12.6-7 after a day or two, that's a bad sign. The sure sign is if you charge it (ans get acceptable voltage) but that the voltage falls below 7volts WHILE CRANKING THE ENGINE then its time to chabge the battery. My batt eventually died (old age and improper care), and while it held 12.4-5 volts i hooked the voltmeter on the batt, layed it on the windshield and checked the voltage while trying to start her; it got down to like 4-5 volts almost right away. I dont have any issues since i got a new battery..

Edited by supernova_6969
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