Low rpm popping

[T77911S]

Originally Posted by Rawknees'Turbo

Just to add some more info to what Jeff and Marco said about the fuel pumps running and the yellow relay - that relay also plays a role in preventing the fuel pumps from running if air is not being drawn over the fuel head, air metering disc. If the fuel head safety switch is plugged in and working (passes an "open/closed" continuity test - switch is activated by the position of the air meter arm), yet the pumps run with the key, then that part of the yellow relay is not working or the pin associated with that function is not making sufficient contact in the socket.

Based on what you describe in post #27, that's likely what you have going on, mas.

he is the closest one to getting right how the FP system works.


think of the FP system as 2 circuits.
1 is the actual FP relays and the the other is the control of the relays.

1:
speed rly (rev limiter) controls the FP rly's
the yel rly controls the FP rly's.
the boost sw controls the FP rly's
2:
the AFM controls the yel rly.

the boost sw provides a gnd for the FP rly's to energize. this gnd goes thru the normally closed (NC) contacts of the yel rly. so the yel rly is DE-ENERGIZED when the pumps are running,
the AFM sw provides a gnd to the yel RLY to ENERGIZE it and turn off the pumps when the engine is not running.

on the US 86 and newer cars you have a speed rly under the seat. this has 2 functions.
1 is to control the O2 sensor, open loop/closed loop. according to the diagram this happens at 3k
the other function, and this is what causes a lot of cars not to run, is the rev limiter function. the gnd for the FP rly's goes thru the rev limiter and to the over boost sw.
the speed rly is prone to bad solder joints,. (actually the other way around for those that want to nict pick),

[T77911S]

not sure how this got to the FP's not working.

[mas88s]

yes
by the book
by the way...thanks for hangin in there Marco

[mas88s]

My fuel pressure is right on the button.
ccp is 2.75 bar
wcp is 3.75 bar
systm pressure is 105+ psi
or am I misunderstanding FP"s

[Mr9146]

Since I don't memorize this crap, here's the spec book:

[Mr9146]

Your fuel pressures look pretty spot on.

Now you have to check other things:

Have you checked the warm up regulator plug for power with the key on? The WUR gets its power from the rear fuel pump circuit.

Have you looked at the pins in the plug to make 100% sure they are all the way in the plug? If you're have problems periodically, and if you have changes to the way it runs after you mess with the plug, look at the plug to make sure the wires aren't pushing themselves out when you remove/install the plug on the WUR. Also make sure that they're not physically damaged (spread, bent, what have you), too.

[mas88s]

The wur is working perfectly.
I plug it in and watch the psi graduate to proper pressure...every time.
How about frequency valve...Andial. Could that be a culprit?
At least i'm getting an education ha ha

[Mr9146]

The WUR might be working, but unless you check the plug for power and visually inspect it for damage you can't be 100% sure the WUR isn't working due to heat transfer from the engine.

Additionally, the test I've suggested allows you to simultaneously check the rear pump electrical circuit.

Everything has a purpose. Do the test.

[mas88s]

Hi Marco,
I did the test twice.
Power at WUR, good ground, plug it in and the pressure goes up.
Do you have a suggestion on where to look next?

[smurfbus]

Cant remember if sparkplugs have been talked here but if the porcelaine is cracked it gives loud banging when hot and popping when not so hot. I have strong spark and I went through several low resistor rotors and copper sparkplugs before I made a diy resistorless rotor and switched to stock platinium plugs. Cheap Copper plugs could not take the heat. Msd 6A, msd helicoil 8mm wires, blaster coil and resistorless rotor with stock plugs.

[T77911S]

i don't know anything about the andial system you have.
if you suspect rich, I would definitely look into that system.

popping is usually a sign of lean, if it is out of the intake, rich pops out of the exhaust. (the last one is based on carbs) with CIS when it is rich it usually surges at idle and the RPM will dip donw then come back up after you let off the gas.

I would try to get a true reading on the mixture if you can.


what you describe sounds more like a lean condition, perhaps an air leak, mixture setting or problem with the lambda system.
you could try to get a reading on the O2 sensor to check mixture.
check the throttle switch. check the wiring to it.


you don't have a pressure problem or a fuel pump problem. idle does not need much fuel.

again, you can manipulate the sensor plate when you start it to see which direction the mixture needs to go. push down and if it runs better it is too lean, up and it runs better it is too rich.

[Mr9146]

Originally Posted by mas88s

Hi Marco,
I did the test twice.
Power at WUR, good ground, plug it in and the pressure goes up.
Do you have a suggestion on where to look next?

It's time to look at the tailpipe and see what's coming out of it if you can. Now that you know the pressures are correct you need to look at fuel mixture (I think the guy above me said that). This is not 100% required, but it'll help to know what's happening at the tailpipe.

At this point the air cleaner should be off the car so you can access the sensor plate and mixture screw simultaneously.

Now, you said the issue is intermittent ... that makes all of this testing and checking a bit sketchy in terms of results, but you need to have the air cleaner off so that you can see things and make adjustments when the car starts messing up.

So, what I would do is start the car cold, get it running, and watch the sensor plate. Does it flutter or does it look fairly stable at idle?

When you put LIGHT pressure on the sensor plate does the idle go up or down? If you LIGHTLY load the sensor plate and the idle goes down you've got a rich mixture. If the idle goes up the mixture is lean. How much you have to move the sensor plate to effect change in idle is a rough estimation of how far you are from "perfect" mixture. Turning the mixture screw clockwise richens the mixture and counterclockwise leans it out. MAKE SMALL CHANGES ... a 1/4 turn on the mixture screw is A LOT of fuel. Go back and forth with pressure on the sensor plate and adjusting the mixture until only the slightest of touches produces a dipped idle. All the while you'll need to be balancing the idle screw to keep idle at around 1000.

Also, when the car is shut off take a look at the sensor plate ... does the gap around the outer diameter of the plate look even? I chased a fueling problem on a RUF turbo motor that backfired in the intake and warped the sensor plate causing all sorts of erratic fueling issues. It was only slight warped, and I barely noticed it, but I changed the plate and the problem was fixed ... now I look at every sensor plate on every turbo I work on when I have the air cleaner removed.

[mas88s]

spent some time on this on Sunday...re-checked pressure. Perfect.
When I press down slightly on metering plate, Idle goes up. Lean condition.
Issue is no longer intermittent. Happens all the time.
Definitely a warm up issue.
I spray a full can of 2+2 in search of a vac leak with no luck .
Not sure if I'm hitting the right places.

This may or may not be pertinent to the cause but when she was warming up I thought I heard a click and everything went back to normal condition. I was around the side of the car and did not hear were it came from. I was not able to replicate it.
Conditions are...when cold I have to start it 3 times. Barely runs, if I apply pedal it pops thru intake and almost stalls.
If I let it get heat soaked, 15 min, runs good. I bought a plx afr meter. I am going to try to get that in this week.

[Mr9146]

So if you know it's lean, and if the issue is no longer intermittent, screw some fuel to it and see what happens.

[mas88s]

Ok
Just an update but I'm still chasing this popping when cold.
Took it to a local shop and he wanted me to remove all aftermarket bs like Adj. waistgate and andial fuel enrichment. Adj waistgate I did remove but the frequency valve is andial...pricey still there.
But as I understand it the frequency valve does its job after warm up.
He also found a bad waistgate, cv boots, front brakes and rotors, steering rack rebuild and column bushing..arrgh.
I just completed all of the above and installed a plx afr meter. sooooo........
Cold
At idle afr's are 12.5
If i lightly accelerate..16-18 and pops
Cruising 2500-4000 15-16
Under boost 11-12.5
Again, after a 4-5 min warm up all popping stops but I feel like the car isn't quite right.
Still fast but not exciting.
Any suggestions???

[Mr9146]

Light pedal gives you 18:1?

Yikes!

I'd add fuel and see what happens

[mas88s]

Went after FV today .
No power at valve.
Pulled drivers seat and noticed relay.
Will replace tomorrow.
It had power at the relay
Should there be 12v at the valve?

[T77911S]

like I asked back in post 18.
does the FV vibrate with the key on?
if the FV does not work it will make it go lean, thus the need to go rich at idle to make it run.


the FV is pulsed on and off so I don't know if you will see 12v or not.
easiest check is does it vibrate.
there is a way to look at the duty cycle on the 911 but I have never done it on the 930 so not sure where you would connect to. you have to use a dwell meter to look at the signal.


I have had the same issue but I have the euro CIS. I had to run very rich at idle, then I am at 15.2 at cruise and also had it go lean when I would lightly accelerate. air leaks for me

[mas88s]

Sorry I missed that.
It does not vibrate.
I replaced the relay and its still dead.
Andial fuel enrichment...
Can it be repaired or should I look for a substitute?
\Thanks

[T77911S]

I don't know anything about the andial stuff.

check for power at the relay( if it is used with the andial).
you could bypass the andial stuff also,.

you can try the dwell meter on the FV but don't know how to connect it to what you have.