Possible vacuum leak? High spark timing at low rpms

N

NJaykaplan

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I just changed the fuel pump, thinking it was a lack of fuel causing the high ignition timing. Definitely needed the pump at 141k. Pulls much harder at high rpms. Car has had upper and lower intake gaskets done already, i changed the pcv valve, no obvious leaks that spraying brake cleaner on the top could find. Any likely hoses by the firewall i should spray and pay special attention to? I don't spray the back as well because i'm thinkin i'm gonna just suck it in the throttle body. Any advice would be appreciated, car is also showing 32psi with vac and 42 with vac off.
 
What are your original symptoms other than just high timing? There are several scenarios where the ECU will advance timing.
 
Was having iac symptoms, iac code until i changed my fuel pump. Now it feels more powerful, but still at low rpms looks like its running lean. I did reset the computer a few times. Also showing fuel pressure at 32psi. I will think of more symptoms later, i really need to datalog more things.
 
Now that i know fuel is no issue, since its a 140k mile car, i watch the trims and spark timing and the timing can go as high as 30-40 under 3k rpms, but over 3k rpms it doesnt go above 30. Also on a regular obd 2 scanner, watching the stft shows it adding fuel. I still cant honestly understand the fuel trims on the sct datalogging but both go from a minimum .75 to 1.2 at idle. I did spray brake cleaner in the top vacuum lines multiple times, so i think its one wrapped up that maybe propane can get to, but the liquid is not.
 
without wide band 02 you have no clue if its lean or rich.
monitoring switching fuel trims is useless, especially if adaptive learning isn't disabled as you are just watching the pcm try to hit a moving target.

sct datalog wont tell you its running lean or rich, you are just watching the 02 sensors switch between rich and lean, nothing more nothing less
 
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The only time i see it pull fuel is when I am WOT, which i assumed wasnt normal. Before the fuel pump job, it didnt idle so well. Occasionally died but was idling very low, setting an iac code. Fuel pressure was 32 and dropped down under load to 20s, so i changed that and hoped there werent any other issues. I mostly watch on a little actron scanner, not the sct, because i dont always have my laptop

For the hell of it, i will list what this car has had done since October when i bought it- Not everything necessarily needed, but this is not my first Mark and i want this one to be as perfect as i can mechanically:

Upper and lower control arms, pcv valve, air and fuel filter, brakes and rotors on the whole car, passenger imrc (96 no less), after the imrc we found a upper intake manifold leak so we did upper and lowers, cleaning the imrc plates as well. Had 2 plug changes in 35k miles, still the acdelco wires on it which were done before i owned the car. (Have wires sitting and waiting which were 40 dollars for acdelco from rock auto, gotta love closeouts) Also, the whole cooling system lol. All aluminum Radiator, thermostat, cobra waterpump. Rear polyuruthane bushings, and then the most recent fuel pump.

In each job i ran a little broke. Still the original tps sensor, iac, i believe old owner changed o2s not 100% but they're still switching pretty fast.
 
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Also, if this is tommy who i think ive talked to before, you said i'm watching the O2s. The STFT and LTFT in sct are just the o2 sensors? that wouldnt make a lot of sense to me, because they do not switch that much. If they were the O2 voltages, i would have switched them a long time ago lol.
 
I really did mean to change the iac, but at the same time it's normally idled perfectly. When the idle did start to act screwy, the first thing i thought of was the fuel pressure just because i spent a lot of time on my 2nd gen trying to figure out its issues, only to find out it had plenty of fuel at idle but as soon as its under load it drops to near 0. Right now it idles perfect as well, but at idle its using more fuel than it normally would. I have no proof, but i deliver food, and had 3 mark viiis. Normally i dont waste so much gas letting it run lol.
 
I also still need to change the fuel pressure regulator. 32 with vac, and 42 with vac removed. I'm undecided on an adjustable regulator, i have a sct x2 but i still have to get it unlocked. I dont have any serious mods, or any real ones for that matter, but i would like to tinker with the fuel pressure. Can the X2 view the injector pulses, so i can watch and see if the ecu changes it at all? I ask because i would pull the vac on the stock FPR, and drive with it, to see what it does running at 42psi constantly.
 
NJaykaplan said:
I ask because i would pull the vac on the stock FPR, and drive with it, to see what it does running at 42psi constantly.
Click to expand...

You do not understand the FPR...

Fuel Pressure Regulator

The fuel pressure regulator (9C968):

~Is attached to the fuel injection supply manifold (9F792) downstream of the fuel injectors (9F593).

~Regulates the fuel pressure supplied to the fuel injectors.

~Is a diaphragm-operated relief valve in which one side of the diaphragm senses fuel pressure and the other side is subjected to intake manifold vacuum.

~Nominal fuel pressure is established by a spring preload applied to the diaphragm.

~Balances one side of the diaphragm with manifold pressure to maintain a constant fuel pressure drop across the fuel injectors.

~Bypasses and returns excess fuel to the fuel tank (9002).
Click to expand...

The fuel pressure is kept at a constant relative pressure.

fpr03.gif


http://fordfuelinjection.com

There are opposing views of the worth of adjustable fuel pressure regulators. I believe they are useful in racing applications to fine tune the WOT fuel pressure for maximum performance but for the average driver little if any difference will be noted.
 
My opinion right off the bat is that you're geek'n out too much about the fuel pressure. also, the fact that you didn't diagnose the IAC valve code and went straight to a fuel pump. Start off with simple diagnosing addressing ALL your check engine codes and then progress deeper. NEVER just replace parts hoping it's going to fix the issue.

That being said, if you had a vacuum leak (unmetered air) you'd still have a check engine light. You mentioned that code earlier but you also mentioned the fixed vacuum leak at the intake so I'm assuming they are hand in hand and it's fixed. If you have to get propane to find a leak, it's probably not big enough to make the car idle bad.

Common things like spark plugs, plug wires, PCV valve, etc can cause fuel issues. The fact that you see the computer pulling full could be because you have a break in a plug wire and the knock sensors are kicking in to prevent detonation. This is a perfect example of a simple issue being over diagnosed.

Lets go back to the basics. What codes do you have now?
 
J said:
My opinion right off the bat is that you're geek'n out too much about the fuel pressure. also, the fact that you didn't diagnose the IAC valve code and went straight to a fuel pump. Start off with simple diagnosing addressing ALL your check engine codes and then progress deeper. NEVER just replace parts hoping it's going to fix the issue.

That being said, if you had a vacuum leak (unmetered air) you'd still have a check engine light. You mentioned that code earlier but you also mentioned the fixed vacuum leak at the intake so I'm assuming they are hand in hand and it's fixed. If you have to get propane to find a leak, it's probably not big enough to make the car idle bad.

Common things like spark plugs, plug wires, PCV valve, etc can cause fuel issues. The fact that you see the computer pulling full could be because you have a break in a plug wire and the knock sensors are kicking in to prevent detonation. This is a perfect example of a simple issue being over diagnosed.

Lets go back to the basics. What codes do you have now?
Click to expand...

The intake leaking never gave me a code, i only found it after we fixed the imrc and it still didnt drive like it had the power i remember in a mark viii. My mechanic sprayed around, telling me it idles too perfect for there to be a vacuum leak, but he found it very quickly spraying along the intake. This was months ago though, if you saw an egr thread of mine i found he didnt reconnect a hose coming from the dpfe sensor on the bottom and it took me forever to realize the bottom wasnt connected.

As far as engine codes, nothing other than one for the secondary air pump. I am kinda stuck on why i only have 32psi fuel pressure, i thought changing the pump would cure it lol. It was the pump causing my screwy idle though. I thought either iac or fuel pump, and since it has 140k miles on the original pump putting a high performance pump in there cant be a bad idea. I drive 5k miles a month so i'd hate for it to die when i'm traveling. In the end, it was sitting at 450 rpms at idle until i changed the pump. I had also reset the battery multiple times just to reset all the computer learned stuff, each time waiting enough time for it to relearn. The only time i had a bad iac, it acted like i had a leak at the throttle how it was revving. I'm just gonna get a hand vacuum pump and test what i can.
 
Now that i think of, the only issue i've actually repaired that threw an engine code so far was the broken imrc actuator when i got the car. The load percent on my actron scanner is 60-80% when idling also, but i have no idea what that is to be honest.
 
NJaykaplan said:
only to find out it had plenty of fuel at idle but as soon as its under load it drops to near 0.
Click to expand...

When you go to WOT the STFT merely displays the lambda value that is commanded by the base fuel table, nothing more nothing less and absolutely USELESS in determing "rich or lean".

Your basing assumptions off alot of flawed data and misconception.
I would suggest leaving that x2 LOCKED until you gain ALOT more knowledge about what you are dealing with.

Tuning your car is not something that you can be spoondfed over a message board.
You want to get to cartechbooks.com and order Greg Banish's book Advance Tuning and Engine Management.
http://www.cartechbooks.com/vstore/...61&St2=-63495&St3=33128&Product_ID=3012&DID=6

You can read portions of that book on the above link, but.. you need to read the whole book it's cheap.
 
NJaykaplan said:
Now that i think of, the only issue i've actually repaired that threw an engine code so far was the broken imrc actuator when i got the car. The load percent on my actron scanner is 60-80% when idling also, but i have no idea what that is to be honest.
Click to expand...

Something is hideously wrong. Load at Idle should be in the 25%-32%ish MAX range.
60-80% is what you would expect to see at WOT

(excerpt from gregs book regarding load)
"Datalogging of the engine sensor data during a wide open throttle run reveals the actual air consumption. This air consumption is used by the PCM to calculate engine load. Notice how this naturally aspirated engine develops approximately 86% engine load at WOT."

no tuning should be attempted until all the gremlins are found and resolved.
you cant properly tune a car that isn't running properly to start with, and you shouldn't try to fix issues with the car by adjusting the tune.
 
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