914-SHO Surging RPMs - Issue Solved?

[3d914]

Well spent the morning running the motor again and are getting similar results. That is cold start, with throttle set at 1800rpm, is bogging around 1000-1200 surging. Once warmed up, settles at 1800rpm and surging is +-100rpm.

Here's what I'm seeing from component testing.

ISC/BPA
Did several tests on this and here are the results

1. Start engine & disconnect ISC solenoid - RPMs should drop or engine stalls.
   RPMs increased instead of decreasing/stalling.
2. Key Off, Disconnect ISC connector, check resistance between VPWR & ISC signal - should be 7 to 13 ohms.
   I measured 13.2 ohms.
3. Key Off, with ISC connected, check voltage between VPWR & ground - should be 10.5 volts or more.
   I measured 12.03 volts.

O2 Sensors
Tested these also:

1. Connect between HEGO signal and ground. Run engine for 2 minutes at 2000rpm - voltage should be .5v or more.
   Both HEGOs were bouncing all over between .1 and .88
2. Key Off, Check voltage between power at HEGO and ground - should be 10.5 volts or more.
   I measured 13.3v on both.

Fuel Pressure
First test.

1. KOEO, Check fuel pressure - should be 31-41 psi.
   Mine jumps to just over 40psi then settles to 38psi. This is with the return fuel line crimped to maintain some back-pressure. If I KOEO again, it jumps to over 60psi, again then almost 100psi
2. With engine running, check fuel pressure at idle (at 2000rpm) with vacuum line at regulator connected - should be 28-34 psi.
   Measures over 100psi with vacuum line connected.

Second test - hour later.

1. KOEO, Check fuel pressure - should be 31-41 psi.
   Mine jumps to just over 40psi then settles to 38psi. This is with the return fuel line crimped to maintain some back-pressure. If I KOEO again, it jumps to 40psi again.
2. With engine running, check fuel pressure at idle with vacuum line at regulator removed - should be 22-32 psi.
   Measures 42psi with vacuum line removed.
3. With engine running, check fuel pressure at idle with vacuum line at regulator connected - should be 28-34 psi.
   Measures 32psi with vacuum line connected.

Conclusions
From test results and first fuel pressure test I was thinking that high fuel pressure caused by failed regulator was causing flooding, surging, and fowling of O2 sensors. Cold start RPM increase when ISC was unplugged was due to excessive fuel + increased air = rpm increase. Like adding air to a flooding engine.

With the second fuel pressure check being somewhat close to spec, I'm thinking the O2 sensors, though cleaned, are still fowled and causing surging conditions. I think it will take another cold start with good fuel pressure to verify this.

Thoughts?

 

[rubydist]

if the thing idles at 1800 rpm with the iac disconnected, that means the throttle plate does not shut far enough, or there is a significant vacuum leak in the intake somewhere.

added fuel alone will not make it go 1800 rpm rather than 700 - there is not enough air for that unless one of the above problems exist.

 

[3d914]

if the thing idles at 1800 rpm with the iac disconnected, that means the throttle plate does not shut far enough, or there is a significant vacuum leak in the intake somewhere.

added fuel alone will not make it go 1800 rpm rather than 700 - there is not enough air for that unless one of the above problems exist.

rubydist, it may not have been obvious, but I mentioned that I have the throttle set at 1800rpm. I don't have a throttle cable, so I have the set screw set there for breakin - since this can't occur properly at normal idle.

Even with that set, it bogged at startup instead of staying where it was set.

 

[hawkeye18]

I'm fairly certain 100psi is too high.

Edit: You did make sure to rotate each injector save for #4 40° counter-clockwise as viewed from the top of the injector as installed, right? I don't know how much of an effect that would have if you didn't.

 

[3d914]

I'm fairly certain 100psi is too high.

Edit: You did make sure to rotate each injector save for #4 40° counter-clockwise as viewed from the top of the injector as installed, right? I don't know how much of an effect that would have if you didn't.

Jason, I did do the rotation, which appears to be to accommodate the connectors. What's weird is that the second time I did the fuel pressure test it stayed at 40psi at KOEO and 32psi while running. I'm going to run it again tomorrow and monitor the fuel pressure to watch for any changes. If it stays consistent, then I may go ahead an buy replacement O2 sensors - since they are the one component still showing erratic results.

 

[intimdatr]

I thought our computers didnt like you messing with that screw to set the throttle plates and would try and combat that back down the 900rpm idle target?

 

[Mr Anonymous]

rubydist, it may not have been obvious, but I mentioned that I have the throttle set at 1800rpm. I don't have a throttle cable, so I have the set screw set there for breakin - since this can't occur properly at normal idle.

Even with that set, it bogged at startup instead of staying where it was set.

I thought our computers didnt like you messing with that screw to set the throttle plates and would try and combat that back down the 900rpm idle target?

Correct. SHO 101: Adjusting the throttle stop screw is not how to set the idle since the PCM will always try to get the idle back to ~800rpm. If you want to change the idle, you have to change the rpms that the PCM is commanding which means a chip, TwEECer, etc. Ignore every other issue and code until you get the idle stop screw back where it belongs and the motor idling properly with what the PCM is commanding.

No need to dick with an 1800rpm idle just to "break in" a motor. Get the motor idling right and break it in on the street, strip, or dyno at WOT.

The whole crimping the fuel return line to create "more backpressure" has probably overwhelmed the stock FPR and rendered it useless. Why reinvent the wheel?

 

[rubydist]

rubydist, it may not have been obvious, but I mentioned that I have the throttle set at 1800rpm. I don't have a throttle cable, so I have the set screw set there for breakin - since this can't occur properly at normal idle.

Even with that set, it bogged at startup instead of staying where it was set.

yup, I missed that.


as mentioned, the pcm will not like that. 2 things will happen. First, when the engine is cold, it will take more air/fuel to make it run at that rpm, so it will "bog" or run more slowly until the engine starts to warm up.

Second, the pcm will assume that the iac is sticking (since that happens all too often) and about every 5 seconds will "blip" open the iac hoping to get it to shut properly. So, if the iac is connected, expect the idle rpm to surge approx every 5-6 seconds as the pcm tries unsuccessfully to gain control of the idle rpm.

 

[3d914]

Correct. SHO 101: Adjusting the throttle stop screw is not how to set the idle since the PCM will always try to get the idle back to ~800rpm. If you want to change the idle, you have to change the rpms that the PCM is commanding which means a chip, TwEECer, etc. Ignore every other issue and code until you get the idle stop screw back where it belongs and the motor idling properly with what the PCM is commanding.

Thanks Chris - this maybe SHO 101 but it's the first it's been mentioned and I haven't read it in any of the books I have. So I guess that becomes my next task is to get a 1/8" orifice (or hose wit a 1/8" ID?) to manually set the base idle.

No need to dick with an 1800rpm idle just to "break in" a motor. Get the motor idling right and break it in on the street, strip, or dyno at WOT.

I disagree under my circumstances - as it will be a year maybe more until the project is finished, so the bench is the only place I have at the moment. And as you know attempting to seat new rings at idle is counter-productive.

The whole crimping the fuel return line to create "more backpressure" has probably overwhelmed the stock FPR and rendered it useless. Why reinvent the wheel?

Not. Just mimicking the "duck-bill" on the return line since I'm just running the return fuel line to my gas can (again - think bench test). Without this there is nothing to maintain 20+psi for five minutes once the motor is turned off.

yup, I missed that.

as mentioned, the pcm will not like that. 2 things will happen. First, when the engine is cold, it will take more air/fuel to make it run at that rpm, so it will "bog" or run more slowly until the engine starts to warm up.

Second, the pcm will assume that the iac is sticking (since that happens all too often) and about every 5 seconds will "blip" open the iac hoping to get it to shut properly. So, if the iac is connected, expect the idle rpm to surge approx every 5-6 seconds as the pcm tries unsuccessfully to gain control of the idle rpm.

Gotcha - so that becomes my next task is to get a 1/8" orifice (or hose wit a 1/8" ID?) to manually set the base idle. In the future I'll start the motor at base idle, then adjust it to the higher RPM to continue break in.

Thanks all.

 

[3d914]

OK, here's a video after I set the base idle. I'm still getting some mild hunting and there is what sounds like an occasional miss.

Base idle video.

Thoughts? I'm out of them at the moment.

 

[LJRuddy]

Not. Just mimicking the "duck-bill" on the return line since I'm just running the return fuel line to my gas can (again - think bench test). Without this there is nothing to maintain 20+psi for five minutes once the motor is turned off.

Okay... But you are the first person I have seen on this forum that posted 100psi on the fuel rail and I have been around SHOs for pretty much a decade now. If you insist on mimicking the 'duck-bill', then at least do it so that you are not rendering the FPR useless. I'm almost certain that this is part of your problems that you are having. :wave:

 

[Off Road SHO]

"Without this there is nothing to maintain 20+psi for five minutes once the motor is turned off."


Gerard, why is fuel pressure in the return line important at this time. All you should care about is the fuel pressure in the rail, on the pressure side of the FPR.

Also, the throttle body stop screw is only to keep the plate from slamming against the throttle body upon lift, and thereby damaging the aluminum body or the brass plate.

What do you need the 1/8" idle hose for again? The whole idle path is built into the throttle body and intake plenum "Y".

Tom

 

[3d914]

Fuel Pressure
First test.

1. KOEO, Check fuel pressure - should be 31-41 psi.
   Mine jumps to just over 40psi then settles to 38psi. This is with the return fuel line crimped to maintain some back-pressure. If I KOEO again, it jumps to over 60psi, again then almost 100psi
2. With engine running, check fuel pressure at idle (at 2000rpm) with vacuum line at regulator connected - should be 28-34 psi.
   Measures over 100psi with vacuum line connected.

Second test - hour later.

1. KOEO, Check fuel pressure - should be 31-41 psi.
   Mine jumps to just over 40psi then settles to 38psi. This is with the return fuel line crimped to maintain some back-pressure. If I KOEO again, it jumps to 40psi again.
2. With engine running, check fuel pressure at idle with vacuum line at regulator removed - should be 22-32 psi.
   Measures 42psi with vacuum line removed.
3. With engine running, check fuel pressure at idle with vacuum line at regulator connected - should be 28-34 psi.
   Measures 32psi with vacuum line connected.

Okay... But you are the first person I have seen on this forum that posted 100psi on the fuel rail and I have been around SHOs for pretty much a decade now. If you insist on mimicking the 'duck-bill', then at least do it so that you are not rendering the FPR useless. I'm almost certain that this is part of your problems that you are having. :wave:

Ruddy, the reason I would see 100+psi on the fuel rail is because I'm using an aftermarket FP (155 psi pump). I was assured this would not override the stock pressure regulator.

Also, I added a quote from my initial tests and only the first test showed 100+. Subsequent tests and while setting the base idle, its been sitting at less than 40 psi. All this with the "duck-bill" in place. I can't explain why the 100psi event occurred either - that's what seems weird. I'll leave the fuel pressure gauge on so that I can track any further anomalies.

 

[3d914]

"Without this there is nothing to maintain 20+psi for five minutes once the motor is turned off."

Gerard, why is fuel pressure in the return line important at this time. All you should care about is the fuel pressure in the rail, on the pressure side of the FPR.

Just trying to mimmic the stock system so as not to induce any side affects. Lord knows I have enough of those already.

Also, the throttle body stop screw is only to keep the plate from slamming against the throttle body upon lift, and thereby damaging the aluminum body or the brass plate.

What do you need the 1/8" idle hose for again? The whole idle path is built into the throttle body and intake plenum "Y".

Tom

I understood the stop screw was used to set the base (mechanical) idle adjustment. Page 180 of the engine manual covers the base idle adjustment. Your notes on the page indicates a 1/8" orifice is needed between the canister purge hose and the PCV hose.

 

[Off Road SHO]

The cannister is never purged at idle and only after a preset amount of time has passed. It has nothing to do with the idle. I think you are causing yourself more grief than is necessary.

My notes? You believe something an old fart like me writes?

Tom

 

[rubydist]

I think it sounds just fine and you are being overly concerned. I would put it in the car and run the heck out of it... enjoy it!

 

[Shovert]

Is the duckbill you mention is it the one that is one the fuel pump system in the tank? If so I got one on a Mustang fuel pump mount. You can have if it will help. Just pm me. Maurice
I looked in the Ford book I have it is called a Check Valve. I found a site that said available at autozone. Could not confirm my antivirus said virus was on that site.
Or have entire unit minus pump. If need electrical connector if decide on submerged pump I have extra. Maurice

 

[Flintstone Chaz]

Running it at 1800 RPM unloaded doesn't take much throttle I assume. Maybe the TPS isn't getting the message to the computer that the throttle is cracked open and it is trying to fix the idle as suggested earlier. Is the TPS adjustible? Could you turn the TPS a little to assure it is telling the computer the engine is off idle?

Charlie

 

[Shovert]

My thoughts, Install fuel regulator before the engine since using a differant from Ford. I agree o2 may fouled up. Do you get codes and what? If tps comes up. I would check at computer. I always try and check sensors at the computer especially if I mod the wiring. Easy enough to goof up. If read at computer eliminates wiring problems.
I assume check for vac leaks. I use a pressurized test to test mine. [learned this doing turbo]. I assume check iac for leaks, also EGR can leak thru. My thoughts, hope that helps. Maurice

 

[rubydist]

tps is not adjustable.