Jury Rigged Fuel Pump and Strange Behavior

[mentalite]

Hi guys.

This is the first of probably many threads and questions as I work through some of the issues on my newly acquired '77.

The previous owner installed a fuel pump switch on the center console and he reminded me to use it especially upon shutdown so the pump didn't keep running.  It looks like crap and I can't abide by a rigged up system that could be a safety issue.  The strange thing is that the switch doesn't always have to be on for the car to run.  Here are some of the details from a cold start condition this morning.

• The switch must be on for the car to start.  You can hear the pump buzz as soon as you flip it.
• The engine idles roughly and smokes like hell, but it will continue running with a slight lope.  The engine will rev fairly smoothly.
• If I flip the switch off after the car is running it smooths out, quits smoking and continues to idle at around 900 rpm.
• Attempting to rev the engine with the switch off will immediately stall the engine, but this can be staved off by flipping the switch quickly back on.
• All plugs are badly fouled and the tailpipe is sooty.  Running extremely rich?

I find this quite perplexing.  It seems that switching off the fuel pump should kill the car right away under all conditions.  Any thoughts?

 

Edited December 30, 2016 by mentalite

[Zed Head]

How long will it idle with the pump turned off?  Could just be residual pressure from flexible fuel lines.  I'd let it idle until it dies to be sure.

The fact that it runs rich when the pump is on indicates that you have one or more of the common Z EFI problems.  Do not adjust the AFM, unless it's already been messed with.  If you find that, adjust it back to where it started.

Your best path to getting it running well is to go through the tests in the EFI Guide.  Clean and check all of your electrical connections.  Read through the Engine Fuel chapter of the FSM and you'll see how the fuel pump circuit works and why the PO added that switch.  If the engine runs right you shouldn't need it.  It's a band-aid.

[Patcon]

A fuel pressure gauge on the fuel rail would help your diagnosis. That way you can watch fuel pressure in real time and compare it to the symptoms. Also if the fuel pump is a later model aftermarket pump and not regulated it could be overpressuring the system resulting richness and plug fowling

[charliekwin]

I wouldn't be surprised if the switch was added to replace a bad fuel pump relay.  I would start by removing all the custom work and getting things wired up properly then run through the EFI tests as suggested.

[Zed Head]

All it really takes is one vacuum leak causing a low idle speed to allow the AFM vane to get too low and voila, a switch is installed. I would start by running the tests in the EFI Guide and/or the FSM. There's a test for the combined EFI/pump relay.

It runs now, which is way ahead of many people's projects. If he removes stuff and it stops running then he's in a whole 'nother world.

[mentalite]

9 hours ago, Zed Head said:

How long will it idle with the pump turned off?  Could just be residual pressure from flexible fuel lines.  I'd let it idle until it dies to be sure.

The fact that it runs rich when the pump is on indicates that you have one or more of the common Z EFI problems.  Do not adjust the AFM, unless it's already been messed with.  If you find that, adjust it back to where it started.

Your best path to getting it running well is to go through the tests in the EFI Guide.  Clean and check all of your electrical connections.  Read through the Engine Fuel chapter of the FSM and you'll see how the fuel pump circuit works and why the PO added that switch.  If the engine runs right you shouldn't need it.  It's a band-aid.

I let it run for ten minutes and finally turned it off.  I crawled under and couldn't hear the pump running.  I wonder if there's some suction in the system once the engine is running.  I was thinking that there was a problem with the cranking part of the fuel pump circuit, but the signal from the AFM was good, thus allowing it to keep running once started.  Not hearing the pump run killed that idea.

I'll just start at the beginning of the diagnostics as suggested.  This should be fun.....electricity and multi-meters seem like some sort of dark art.  It just never makes sense to me!

Anyone know of a photo or diagram of the engine bay showing what's where?  The FSM doesn't seem to have one and wires and vacuum lines run to all sorts of interesting contraptions.

Edited December 31, 2016 by mentalite

[mentalite]

Oh yeah...step #1 will be to remove and check every connection.  Would dielectric grease be recommended before reconnecting?

Step #2 will be vacuum lines.  Should I completely remove every line to get up close and personal to check for cracks?

Thanks again.

[Zed Head]

Well, the fact that it runs well with the pump off and bad with it on suggests a problem either way.  Knowing fuel pressure is important.  If fuel pressure measures correct check the vacuum hose to the FPR for fuel.  IT should be dry.  You can have good pressure but too much fuel supply due to a leak through the FPR diaphragm.  Not uncommon to blow a diaphragm and fight a "running rich" problem for weeks or months.  It's sneaky.

Dielectric grease seems like a good idea and wouldn't hurt.  But it makes everything greasy.  If you drive it fairly regularly any corrosion you cleaned of should stay away.  It's the sitting out in the moisture that causes the problem.

There's a diagram at the beginning of the Engine Fuel chapter that is pretty good.  Gets you close.  Most of your measurements will be at the ECU connector though.  Use the 1980 EFI Guide, it's very good.  Covers all years up to 1980.

 

[mentalite]

Thanks, Zed.

I've read that one a couple times now.  Thanks also to whoever had the idea to upload manuals.

[mentalite]

Just a quick update to put a bow on this topic.  Everything had checked out with the fuel pump relay.  Then I poked around under the carpet behind the passenger seat and there were the two fuel pump wires laying there nicely.  Looks like the factory wires from there to the fuel pump were just pulled out and sent to the trash at the time a PO did the direct wire of the pump.

Quick tests right at these wires also showed power when key was in start and when the air flap was moved.  Yay!  Then it became a simple matter of cutting off the wires leading to the pump, putting on bullet connectors and plugging them into the harness.  Luckily to PO rewire job went through the correct grommet in the floor to get to the pump.

Once I started the car and verified all was working as intended I just had to pull out the switch and the wires.  If only all fixes were this easy!

[Chickenman]

Haa Haa. Reminds me of the wiring mess I found from PO of my car. PO said it had a " secret Kill switch " installed by his mechanic for the Fuel Pump" . Yep, there it was. A nice shiny toggle switch coming out of the center console  by your right knee. It was cleverly labelled " Kill " to fool thieves... 

Being the curious type, I decided to toggle the switch while driving. Absolutely nothing happened. Car kept right on humming right along. Tracing the wiring found that someone had hot wired this switch direct from the fuse box to the fuel pump.... but they left the original wiring in place!! Not the brightest electricians in town. Lots of other wiring  nightmare stories involving CB Radio's,  AC " Turbo " switches, " Chromed " alternators that don't work, etc etc.  Fortunately the main engine harness was never hacked...

 

Edited January 13, 2017 by Chickenman

[mentalite]

Oy!   It's becoming clear that a car's best attribute is that PO's have left it alone.