Svo Going Lean

quickerstang · May 28, 2012

I have a 84 SVO it has a 255 intank walbro pump. I added the ground wire and did the single pump conversion. The car goes lean even at low boost 10-11 psi above like 4500. I have a moates quarterhorse tuner and am running the PE binary. Even when I increase fuel by like 30% above 4500 it still goes lean like 12.75:1. This is according to my innovate lm1. As of now I have no fuel pressure guage in the car but I have one on order which may help me to solve the problem. I do have one under the hood and it is set to like 40 lbs with no vacuum. Any ideas? Thanks, Donavan

KhanTyranitar · May 29, 2012

You do realize that at those RPMs, you are in the peak cylinder pressure range, which is right where spark blowout can start happening, even at low boost. This blowout causes misfires, which in turn causes unburned fuel and air, which the sensor will read as lean. If you have anything else going on, it can make it difficult to sort out what is going on. What is your spark gap set to?

Also, what VAM do you have? It is possible that you might have a bad VAM, and it is not reading flow accurately, so the computer is not adding fuel accordingly. You might have to sweep the VAM though its range and make sure it doesn't have any dead spots and that its not sticking.

Just a few things to check, I know figuring out stumbling and such can be really tricky.

Another thing to consider, and its hard to check for, is that if a few valve springs are getting weak, it is possible that at higher RPM that your valves are floating. If this happens, even though you boost is high, your actual cylinder pressures would be low. Just remember, if anything that happens to prevent complete combustion occurs, then you get unused oxygen too, and the O2 sensor or wideband sensor cannot tell the difference between an unburned mix and a lean mix.

I'm not sure if you year has a knock sensor, it is also possible that you are getting knock, and that the timing is being pulled in that range, which will also change the wideband readings, and will show up as a stumble or hesitation. Don't disable the knock sensor to overcome the issue, instead try to figure out how to stock the knock, you might need to pull a degree or two of timing in that part of the timing map.

79'293stang · May 30, 2012

I notice you are running the PE binary. Did you change the injector size? The PE is set for 35lb injectors and in 1984 the SVO's had 30lbs. So if it thinks it has bigger injectors than it does there could be a lean issue.

quickerstang · May 31, 2012

KhanTyranitar said:
You do realize that at those RPMs, you are in the peak cylinder pressure range, which is right where spark blowout can start happening, even at low boost. This blowout causes misfires, which in turn causes unburned fuel and air, which the sensor will read as lean. If you have anything else going on, it can make it difficult to sort out what is going on. What is your spark gap set to?

Also, what VAM do you have? It is possible that you might have a bad VAM, and it is not reading flow accurately, so the computer is not adding fuel accordingly. You might have to sweep the VAM though its range and make sure it doesn't have any dead spots and that its not sticking.

Just a few things to check, I know figuring out stumbling and such can be really tricky.

Another thing to consider, and its hard to check for, is that if a few valve springs are getting weak, it is possible that at higher RPM that your valves are floating. If this happens, even though you boost is high, your actual cylinder pressures would be low. Just remember, if anything that happens to prevent complete combustion occurs, then you get unused oxygen too, and the O2 sensor or wideband sensor cannot tell the difference between an unburned mix and a lean mix.

I'm not sure if you year has a knock sensor, it is also possible that you are getting knock, and that the timing is being pulled in that range, which will also change the wideband readings, and will show up as a stumble or hesitation. Don't disable the knock sensor to overcome the issue, instead try to figure out how to stock the knock, you might need to pull a degree or two of timing in that part of the timing map.

my plug gap is small like .028

I have the large vam and have done a sweep test and it appears to be fine

as far as the valve springs go I had a problem with them before and had replaced them with stock ford explorer springs that I tested. I also did a ranger roller cam swap with a adjustable gear that I pulled 6* out of the cam. the head was also ported at this time

I dont have the knock sensor hooked up and my timing is set at 10* which is stock I believe

quickerstang · May 31, 2012

79'293stang said:
I notice you are running the PE binary. Did you change the injector size? The PE is set for 35lb injectors and in 1984 the SVO's had 30lbs. So if it thinks it has bigger injectors than it does there could be a lean issue.

I did install 35#ers. but good eye!

quickerstang · May 31, 2012

I did get my stuff to hook up my fuel pressure guage, so that will be next and at least it will help me narrow it down

79'293stang · May 31, 2012

How do all your vacuum lines look? I replaced all my vacuum lines just because they were looking kind of hairy and I could not believe how much better it ran.

quickerstang · May 31, 2012

79'293stang said:
How do all your vacuum lines look? I replaced all my vacuum lines just because they were looking kind of hairy and I could not believe how much better it ran.

there pretty good. I got my fuel pressure guage almost done so I should have a clue soon. I hope

quickerstang · Jun 1, 2012

Here are a couple of pics, just for the heck of it
View attachment 148742
View attachment 148743
View attachment 148744

65ShelbyClone · Jun 2, 2012

Have you done any datalogging with the Quarterhorse?

quickerstang · Jun 2, 2012

65ShelbyClone said:
Have you done any datalogging with the Quarterhorse?

yes, but I cant log AFR and fuel pressure as of now

65ShelbyClone · Jun 3, 2012

What about commanded pulse width and airflow? If they both increase as they should while AFR rises, then it suggests fuel pressure is falling off.

I don't have any Moates hardware so I don't know exactly what it can log or how the different binary editors display parameters such as pulse width, like whether it's shown as actual time or a hex value derived from some obscure equation with several multipliers involved(like Nissan). After digging in some old late '80s Nissan .bins with TunerPro recently(trying to find a MAF transfer), I had forgotten how much easier things can be with a speed density standalone.

quickerstang · Jun 3, 2012

It is real time and I will be able to log pressure and afr. I adjust the fuel thru the WOT fuel multiplier. I am going to swap the regulator for the heck of it. I drove it yesterday with the fuel pressure guage and fuel pressue is not increasing with boost. I increast the fuel pressure to 45lbs with the vacuum connected and it actually idled better, but when I took it down the street it ran worst. Fuel pressure does decrease by like 10 lbs instead of increasing by 20 (2lbs per lb. of boost). It I get on it almost full throttle like 3/4 it will actually increase pressure by like 5 psi. I am thinking that it is going to by a bad pump issue, since the car drives ok at part throttle but craps out at full load.

65ShelbyClone · Jun 3, 2012

You're supposed to set the base fuel pressure with vacuum disconnected. 45psi at idle with vacuum is around 60psi baseline plus whatever the regulator increases it to under boost. Are you using an FMU or other rising-rate regulator of some sort?

quickerstang · Jun 3, 2012

65ShelbyClone said:
You're supposed to set the base fuel pressure with vacuum disconnected. 45psi at idle with vacuum is around 60psi baseline plus whatever the regulator increases it to under boost. Are you using an FMU or other rising-rate regulator of some sort?

I know I just bumped it up with it connected to see how it would run. It only goes up like 5 psi with vacuum disconnected not 15. I am running a bbk regulator. I dont have a fmu these cars dont need one. Dosent fuel pressure go up when pressure enters the vacuum port on the regulator?

dbentesr · Jul 16, 2012

One thing I have learned from increasing fuel pressure from the fuel pump forward is that many times an increase in the size of the fuel lines is needed to prevent a car from "leaning" out. A suitable increase in fuel lines size should be researched in your case. You may increase to 6# fuel line size from the tank forward and it should take care of your issue if you have not found another solution prior to trying this.

Svo Going Lean

quickerstang

New Member

KhanTyranitar

Member

79'293stang

Active Member

quickerstang

New Member

quickerstang

New Member

quickerstang

New Member

79'293stang

Active Member

quickerstang

New Member

quickerstang

New Member

65ShelbyClone

quickerstang

New Member

65ShelbyClone

quickerstang

New Member

65ShelbyClone

quickerstang

New Member

dbentesr

New Member

Similar threads

Svo Going Lean

New Member

Member

Active Member

New Member

New Member

New Member

Active Member

New Member

New Member

New Member

New Member

New Member

New Member

Similar threads

Privacy & Transparency

Privacy & Transparency