DHLA 40 question. Running pig rich!

[spoolin4life]

On 6/21/2020 at 12:00 PM, jonbill said:

when you tested compression, did you do it with the throttle open?

Hey Jon refer to my recent reply. Maybe you know what it's not getting fuel. Scared the heck out of me. New engine started misfiring but then did a compression test and it was 150psi across the board

[jonbill]

I'm not sure I understand what you mean by "after" a pull. Are we talking about high rpm WOT or high rpm on closed throttle?
If the former, I'd be looking at the air correctors. they are quite big at 195 so could be making it lean above 6k rpm.
if the latter, it really shouldn't matter.
could you maybe sketch how the AFRs vary with engine speed and throttle position?

[spoolin4life]

10 minutes ago, jonbill said:

I'm not sure I understand what you mean by "after" a pull. Are we talking about high rpm WOT or high rpm on closed throttle?
If the former, I'd be looking at the air correctors. they are quite big at 195 so could be making it lean above 6k rpm.
if the latter, it really shouldn't matter.
could you maybe sketch how the AFRs vary with engine speed and throttle position?

So if I'm driving around just cruising it's very rich at 8-9ish. But if I go WOT to 4500rpm I'm still rich at 9ish. I haven't pushed the car passed 5000 rpms ever. But as soon as I let off the gas the afrs go to 22 and stay there for a while (yesterday was well over 15 seconds at 22) until it starts misfiring. That's when I noticed the misfire again on the new engine. Luckily it went away when I richened the mixture screws and I don't think it harmed anything. Even when I rev the car briefly it goes pig rich and when I let off the throttle it'll go super lean for 6-7 seconds. That's far too long even for efi. 

My guess at this point would be sticky floats. I wish I knew more about these cars and how side drafts work ? 

 

 

Edited June 24, 2020 by spoolin4life

[jonbill]

confusing.
you don't want to be running it much at 8 and 9, you'll have a sump full of fuel!
if you lift off and close the throttle at 4000, its ok for it to go to 22. there's no load and only enough fuel for idle. As the revs come down towards the idle range the AFRs should come back down until its idling as it was at the start.
is it staying at 22 when the tevs are back down to idle speeds?

I don think it would be sticking float valves.
how old is you wbo2 sensor? flipping between super rich and super lean might be a dead or clogged sensor.

[spoolin4life]

18 minutes ago, jonbill said:

confusing.
you don't want to be running it much at 8 and 9, you'll have a sump full of fuel!
if you lift off and close the throttle at 4000, its ok for it to go to 22. there's no load and only enough fuel for idle. As the revs come down towards the idle range the AFRs should come back down until its idling as it was at the start.
is it staying at 22 when the tevs are back down to idle speeds?

I don think it would be sticking float valves.
how old is you wbo2 sensor? flipping between super rich and super lean might be a dead or clogged sensor.

Ya I don't wanna wash the cylinders out.  I don't think the wideband is faulty, it's roughly a year old and I bought it used. I mean I have a spare i could try installing. But when I did an oil change on the old engine it did reek on fuel so I know the wideband is correct on that end and when it went super lean yesterday that's when it misfired during driving so it seems accurate. The sensor bung is located roughly 2 feet back from where the pipes merge from the stock exhaust manifold. Maybe it's to far down? But it shouldn't be doing this when I have the mixture screws turned 2.5 turns out. 

And yes it stayed at 22 at idle speed for quite some time after the one WOT pull to 4000rpm. That's when it experienced the misfire. Ya very confusing. I'll have to check my fuel pressure as well. 

 

[jonbill]

maybe your float valves are sticking or your fuel pressure is too low. I reckon full float chambers allow you to drive gently for say 3/4 mile. so a couple of full throttle runs might empty them, and then if the valves are blocked or no fuel pressure it could take 15 seconds to fill again at idle. should be easy to prove.

[spoolin4life]

4 minutes ago, jonbill said:

maybe your float valves are sticking or your fuel pressure is too low. I reckon full float chambers allow you to drive gently for say 3/4 mile. so a couple of full throttle runs might empty them, and then if the valves are blocked or no fuel pressure it could take 15 seconds to fill again at idle. should be easy to prove.

That is the logic I deduced as well. If the floats aren't allowing fuel into the bowl after a heavy throttle pull then there's nothing continuously going in.

So amateur question, is the top screw on the fuel pump how you adjust fuel pressure? 

[jonbill]

That is the logic I deduced as well. If the floats aren't allowing fuel into the bowl after a heavy throttle pull then there's nothing continuously going in.
So amateur question, is the top screw on the fuel pump how you adjust fuel pressure? 

I don't know, my car only has the mechanical pump from the factory, so my pressure is regulated by an Aeromotive FPR.

[spoolin4life]

5 hours ago, jonbill said:

8 hours ago, spoolin4life said:

That is the logic I deduced as well. If the floats aren't allowing fuel into the bowl after a heavy throttle pull then there's nothing continuously going in.
So amateur question, is the top screw on the fuel pump how you adjust fuel pressure? 

I don't know, my car only has the mechanical pump from the factory, so my pressure is regulated by an Aeromotive FPR.

I have just the stock mechanical pump but I'm assuming it's the top screw. I'll have to try playing with it when I put a fuel pressure gauge in line. Is there a chance it's something vacuum related that could cause this? 

[jonbill]

I never heard of adjusting the pressure of the mechanical pump.
I'd start with getting a pressure gauge and inserting it in the fuel supply line to a carb.
if it passes that test, then maybe take the top off one, including the valve and check theres a good flow of fuel when the valve is open.

[spoolin4life]

On 6/24/2020 at 2:12 PM, jonbill said:

I never heard of adjusting the pressure of the mechanical pump.
I'd start with getting a pressure gauge and inserting it in the fuel supply line to a carb.
if it passes that test, then maybe take the top off one, including the valve and check theres a good flow of fuel when the valve is open.

The carbs are getting roughly 3.5psi each. I found out my return line was closed and when I went to open it the car wouldn't even run properly at all - made the car run even worse than before. I feel like like you don't need a return line with the dhla 40s. 

I don't have a fpr. Just the stock mechanical pump. Do you run a return line?

[jonbill]

3.5 psi is a good pressure, but if you loose pressure with the return line open, maybe the pump isn't moving enough fuel. can you install that pressure gauge so you can see it when you drive? it would be informative to know what happens with the pressure when you have that lean condition.

if thats a pain, I'd be inclined to try adding a cheap inline electric pump. you've probably got wires for one down at the fuel tank sender.