MFI troubleshooting - high idle, pops and bucks at part throttle

[edmayo]

I've seen too many messed up carb tunings to buy that!

[Arne]

Mark called and said my pump was delivered to his shop this afternoon, so perhaps we'll have an idea what's wrong before too long.

On the other hand, I'm still aware that the pump may not be the root of my problem. But I need to eliminate that as a possibility before I go any farther.

The good thing on this is I'm hoping that a freshly calibrated pump will be close enough to correct when I get it back on the car that I can leave it alone while tracking down the real problem (assuming it still exists). Or maybe it will run great and I can move on to other things!

[Arne]

Talked to Mark this morning, my pump and injectors are on their way back home - inspected, serviced, cleaned and calibrated.

As for "THE PROBLEM", when Mark first looked inside he he was fairly sure he found the issue, but after bench testing he's not as certain. Perhaps he'll post here to explain better than I can. But what he first saw was that the shutoff solenoid was adjusted such that he felt it could be accidentally shutting off the fuel at times once the thermostat pushed the rack into the fully warm position. Unfortunately the initial bench test did not duplicate the issue. But it is still possible that when on the car this was the issue, as the pump has been bounced around by UPS on its way to Mark, and that could have changed things a tiny bit.

In any case, that has been corrected, and everything checks out great now, ready to bolt back on the car.

Mark also suggested - once we got to chatting about the shutoff solenoid - that perhaps I could have an electrical fault that is triggering the solenoid when it should not be triggered. I have checked the microswitch, which appears to be working correctly, but that is not all of the circuit. Therefore, when I first test it after reassembly, I will NOT connect the solenoid. If all runs well (other than popping exhaust) with it disconnected, I can try reconnecting it to see if the problem reappears.

I'm actually somewhat optimistic for the first time in quite a while. Because a shutoff solenoid problem of some type is the first theory that truly covers most of the symptoms. Here's hoping...

[edmayo]

Got my fingers crossed for you! The solenoid is NOT something that one normally fiddles with ! But, like others, I have seen some strange stuff. Had one a few months ago that would run pukey rich no matter what adjustments were made. Turns out some one had removed half the thermostat shim stack,,,arrgghhhh

[Arne]

Half the shim stack? Sounds like a movie title - Rich and Richer...

[JT912]

Half the shim stack? Sounds like a movie title - Rich and Richer...

Arne, close....

https://youtu.be/hG46_SvgtRI

[Arne]

Sigh... So close.

The pump and injectors were delivered this afternoon, I have got it all reassembled.

Now I have a new issue. It starts right up, but will only stay running while the key is in the Start position. As soon as I release the key and it falls back to Run, the engine dies as if I have shut it off. Normally, I'd assume this was a bad ignition switch, but when tracking this in the wiring diagrams it looks like the coil/CDI don't get power on a separate wire from the switch. And all other electrical bits work fine. Fuel pump runs, headlights come on with the key, turn signals and gauges, wipers, everything.

I'm not seeing separate feeds from the switch to power the coil/CDI from Start and Run, so I'm thinking there must be a relay involved somewhere.

Any likely connections that I could have disturbed in the back while working?

[edmayo]

Since this all worked before, and all you did was R & R the pump, the ignition switch must have been on the way out. It is a straight forward circuit for the ignition, power from 15 of the ign. switch to fuse 7 which is bussed to fuse 8, from fuse 8 to term. B of the CD box. Pull the plug from the CD box, put the red lead of a voltmeter to the middle term. of the removed plug, and the black lead to ground. Turn ign. to crank,,,you should see 12 volts, then return ign. switch to 'run' position, you should still see 12 volts. If not the electrical portion of ign. switch has gone south.

[2.5MFI]

When the MFI pump and injectors are removed for service and then reinstalled it takes a hole lot of starter motor cranking to bleed out all the air in the fuel lines before the engine will finally run and idle. Maybe what's happening is the cold start system is firing the engine during cranking like it should (fuel squirting in the intakes) then when you back-off the key to run it dies because fuel lines are still pushing air.

[Arne]

When the MFI pump and injectors are removed for service and then reinstalled it takes a hole lot of starter motor cranking to bleed out all the air in the fuel lines before the engine will finally run and idle. Maybe what's happening is the cold start system is firing the engine during cranking like it should (fuel squirting in the intakes) then when you back-off the key to run it dies because fuel lines are still pushing air.

This is apparently what is happening. If I disconnect the cold start solenoid it doesn't fire at all. Reconnect it and it fires until I release the key, then dies.

I knew I'd need to crank a bit to purge the air out, but man alive, it is taking a really long time. I've cranked it (with cold start disabled) for several minutes now, no real signs of life yet. Taking a break for a bit to make sure I don't overheat the starter motor. Will keep at it.