Running Lean (but not mean)

[beatnavy]

After tinkering and tuning and toying for months I've got the "red onion" almost running beautifully. I've been chasing and eliminating potential or actual vacuum leaks and replacing anything else that may be a stealing from my performance and reliability. Right now I'm down to two outstanding items (at least on the engine):

1. Wandering dwell (I'll raise question in a separate thread), and

2. Exhaust popping/light backfiring. So from research and everyone's help this is probably either a lean condition or exhaust leak, and now I'm pretty sure it is the former. I say this because this week I installed one of 914Ltd's spacer's for the CHT to slow down warm-up sensing in the ECU. That was about the best $22 I've spent (at least on a car). I know it was primarily for the 2.0, but the car runs much better cold now, and NO popping/backfiring when cold to cool. There is still some VERY light popping when warm. So if my reasoning is correct here, the spacer is probably helping enrich the mixture while the engine is cool, but once the CHT gets to something approximating "normal" temp I'm back to a slightly lean condition. So the irony is my teener seems to perform slightly better when cold right now.

My questions are: Is my reasoning generally sound? Based on this, is the best/only way to enrich the mixture just to increase fuel pressure? I try measuring the fuel pressure at the rail, but I can only approximate it. My cheap-ass gauge bounces around 29 psi give or take 2-3 psi. Not very precise I know. Bonus question: can someone tell me the type/size of the bolt that plugs into the fuel rail? That's where I'm checking fuel pressure (with a rubber hose coming off that), and that bolt is almost stripped. I suppose I need to double check for vacuum leaks, particularly near the injectors.

'72, 1.7L Stock D-Jet with early ECU (no idle knob).

As always, TIA!

[sixbanger]

Don't fool with striped threads when it comes to fuel. I'd look at the points, valve sticking or A valve that might be to tight. You may have a carb problem also.

[sixbanger]

Only use a gauge that has a hose with a threaded end. Don't use hose clamps on a rubber hose. Did you check the float level?

[sixbanger]

Sorry I thought you had carbs.

[beatnavy]

No sir, stock FI. Yes, my points may be contributing to the issue as referenced in my other "issue."

[porschetub]

Originally Posted by beatnavy

No sir, stock FI. Yes, my points may be contributing to the issue as referenced in my other "issue."

An increase in fuel pressure will do nothing for you,the only way to get that is with a higher pressure fpr and it may tax your existing injectors (leakage) or just fire more back to the tank via the return line.
The bottom line is there is a whole heap of stuff on your car that can go wrong,I still think you should the ditch the points and go for Pertronics,if you have a wandering dwell issue then most likely you have a worn dizzy or the best part is you fit it and never go in there again...one variable out of the loop.
Is your engine basically sound are the valves set spot on?keep checking you are getting close,whats your idle speed when warm for instance.

[beatnavy]

Hey Porschetub!

All good points. I've adjusted and rechecked my valves a couple of times, and I think they are good (to the best of my somewhat limited experience). When the dwell is in range and the timing is set and the lines hooked up correctly and the bleed screw adjusted I do get a nice steady idle (for the most part) through cold to warm engine. I do have a new TPS board on the way, as it was determined that my idle-circuit trace is missing. Somehow idle is still pretty good even without that trace.

I can only otherwise assume that the basic engine is sound. I don't know the history of it other than it had sat in barn and yard for quite a long time. What I do know is that when things ARE where they should be it does perform like a champ and gives me all I could expect from a 1.7 (IMHO).

Eliminating variables is a good thing. I may just have to go with a pertronix or pertronix-like solution soon. While I like the idea of not futzing with dwell and points, I feel like from what I've read here and on 'the world' that they can open up other issues.

Thank you my friend.

[Dave at Pelican Parts]

Originally Posted by porschetub

An increase in fuel pressure will do nothing for you...

That's not quite true. Increasing the fuel pressure will make the mixture richer across the board. The injectors will be open for the same amount of time, but higher pressure will push out more fuel during that time. Going up a couple of PSI should not hurt anything.

That said, richening the mixture may very well not fix the problem--or might be a band-aid for something else.


A wandering dwell means your distributor is worn and needs rebuilding. There is a non-zero chance that a worn distributor could be causing your popping, depending on exactly what is worn and how. I'd give a very serious thought to rebuilding that.

--DD

[beatnavy]

Thanks Dave. Always appreciate the help. I will experiment with slight increases in fuel pressure tomorrow. In terms of distributor rebuild...I assume you mean something more than a "reconditioning" which I did about 8 weeks ago: thorough cleaning, new advance plates, etc. Do you mean replacing/repairing some of the more fundamental parts?

[Dave at Pelican Parts]

I mean doing all of that stuff, plus replacing the shaft bearings. Because if the stuff you did has not fixed the wandering dwell, it is very likely that the shaft is wobbling.

--DD