I have always had somewhat of a hard, irregular warm/hot starting issue. Even before I converted to MAF. I kinda chalked it up to a 2G alt, older battery cables, even old ECT and ACT(IAT) sensors.

Well, let's fast forward. Already swapped In a 3G, new cable for it and my grounds are all good. Verified my ECT & ACT sensor's. O2 sensor is only 2 years old, 8000+ miles, maybe less. Same issue with the rough, coughing warm/hot starts. I also have an AutoMeter Air/Fuel ratio gauge installed. What I have always noticed is that the truck will stay stuck in Lean mode after restarting in the warm/hot situation. It will generally do that until I hit Reverse or Drive and as long as I break the cycle with some throttle control, it will start switching as it should between Lean-Stoich-Rich.
Well, as I watched it do the same thing today, I sat watching it, just in the driveway. No CEL for nearly 15 minutes. I'm confused at this. Well, I unplug the ECT sensor, CEL comes on and I plug it back in. CEL works, so I check the ACT sensor, same thing. So with MAF sensor. Still no switching noticed from the A/F gauge. On a whim, I grab a vinyl vacuum cap, and pull the vacuum line for the FPR off the vacuum tree, and cap it. Finally, the A/F meter starts switching.

I left the FPR unhooked and test drove the truck twice tonight with several hours of sitting allowed. Digital Coolant temp gauge showed 140 the first time and then 90 the second restart several hours later. Each test, I checked for the Lean condition and never once could be noticed. Subsequently, I also checked if the A/F meter registered a Rich condition and never did.

Exhaust doesn't smell rich, no codes, so I'm confused why it runs better and no I'll effect's. I did notice one thing. I can't run my base timing above 10°BTDC. Anything other and I have to run 89 and 12° nearly requires 91 octane. I have verified my advance with the Spout in and it jumps to around 16-17° BTDC, so I know that is working. This is where I miss the SD EFI part, with the Knock sensor on the 302.

I know that not having a WideBand O2 sensor kinda leaves this a guessing game. What I'm curious about is whether when the heads were shaved/milled some, have much did compression raise? They were milled once by Ford Motor Company in 1998 when the engine was rebuilt then. Then my machinist notched off around .005-10, I can't remember, but I know it wasn't more than that. Its also bored 0.040 over, with stock piston's, Comp Cams 31-255-5 cam, w/4° advance. 4-hole pintle injectors from the wife's Expedition I swapped in, Motorcraft coil, Ford Racing wires, Autolite Copper plugs, 0.054 plug gap, Motorcraft EGR Valve, not rebuilt.

I was thinking of playing with the timing again and see if I can bump it a few more degrees since the FPR is disconnected.

Next thought is to buy an Adjustable FPR and do this right.

Can anyone shed some light on this question as to why it runs better with the FPR disconnected?

All ideas, suggestions greatly appreciated!

 

Why spend money on an adjustable FPR when the real issue may be the one you have is bad? Check the fuel pressure......rent a gauge.

 

I'll check the fuel psi today. Though, its a brand new Motorcraft FPR that I installed 2 years ago. I had forgot to mention that in my earlier post.

 

Your engine should go pig rich with the vacuum hose detached from the FPR. Either the FPR is bad or you have another fuel supply restriction, i.e. filter or weak pump.

 

I was thinking it should go pig rich too!!

Pump is 4 years old, filter is 2. I'm trying to get motivated here shortly to check the fuel psi. Weather has gotten chiller since yesterday.

I'll post my result's here shortly.

Thanks again RLA!!

 

Ok, got motivated.

Static psi, 34-36, dropped to 32 psi after 45 minutes.
Engine Running psi 30, blip throttle, jumps to 32-34, then drops to 29, back to 30
Engine Running psi (Vacuum Hose removed and capped) 39 psi

All psi Numbers look within spec. So kinda dumbfounded, but runs like a top! Any other ideas?

I have the gauge still hooked up. Gonna wait an hour and then check psi again and reconnect FPR and check to see if Lean condition is still present, Im sure it will be, but I'll be looking at psi for the hot start.

Also, TPS is set at 0.87 volts, and the idle speed is around 675-725. IAC is Motorcraft, and only 4 years old. Throttle body is BBK and only 4 years old. Running 1.7 Cobra Roller rockers. That's all I can think of as far as parts.

 

Checked fuel psi again. Dropped from 39-30 over an hour. Restarted truck, FPR connected, same psi as before. I watched for nearly 10 minutes, same Lean condition. This time I unplugged MAP sensor, no change, but CEL was on. Plugged it back in. Pulled the TPS connector, and finally got it to start switching AND also a CEL. Engine rpm barely changed. That concerned me because if I had done that with my SD EFI setup, the RPM's would have jumped up to around 1500-1800. Same if I had removed the MAP connector.

Now I'm wondering if I should swap PCM's. I have another A9P and also an A9L PCM. Has anyone had similar problems with a MAF setup using an A9P PCM?

 

The fact the O2 is not switching when the FPR or MAP is unplugged makes me wonder if the O2 sensor is bad or perhaps you have an exhaust leak upstream of the O2 sensor.

 

Ok, so just posting some more information.

Since I last posted, I checked fuel psi again, and now it's nearly 12 psi. So I have either leaking injector, FPR, or pump problem. I also checked to see about my other PCM's I have. I have another A9P and C3W. Now for grins, I open both and find 2 of 3 caps on each PCM have leaked some electrolyte fluid. No damage to board, so just needing some electronic repairs. This has me curious if my current A9P may be suffering from same problem.

Also, the only time the Air/Fuel gauge registered switching was when the FPR and TPS was disconnected.

 

Ok, so I left the fuel psi gauge hooked up overnight. I get up today, and have Zero fuel psi. I don't know whether the check valve in the pump is leaking, or FPR is bad or whether a leaking injector(s).

Weather is crappy, so gonna wait till next sunshine to see if pulling plugs will reveal that problem.

Gonna put some fuel in my front tank and try to rule out rear pump. Has anyone run into the same situation and know whether the slow bleed off is due to injectors, FPR, or pump?

Also, I have a computer repair place here. Will see what they will charge to replace capacitors or if they will even touch PCM's.

 

What you describe is normal. There is a specification listed somewhere for bleed off rate, but IMHO yours is completely normal.

 

Thanks for the info RLA. Reason that has me concerned is because on my '92, 300, if I do the same, it will hold 50 psi for several days, If not longer..but for 10-12 hours, I would figure better than 0. I also notice that once the engine is shut off, psi will raise several lbs and I figure that is normal. Could that be anything I'm missing?