STFT/LTFT Way Off No Codes

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98GTAZ

98GTAZ

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IAT reads the air temperature correctly. I am in Phoenix and it reads a few degrees above the outside air temperature. It was reading 93 degrees when I took these measurements which was pretty close to the outside air temperature. Colant temperature reads correctly. From a cold start it rises to 190 degrees. Coolant temperature stays between 190 and 201. Fan kicks in at temps above 201. I am using an AutoPHIX scanner to get these readings.
 
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98GTAZ

98GTAZ

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I did another smoke test. Introduced the smoke at the IAT sensor hole in the CAI. Had the throttle body propped open.

Each time I introduced smoke I saw smoke rising from the front of the intake just behind the alternator. It consistently always rose from between two of the intake runners just behind the alternator.

Given this, I am thinking this is an intake manifold vacuum leak that is slowly getting worse.

Should I just replace the manifold or are there other items to test? If I do replace the manifold, which manifold should I use?

The car is a 1998 with NPI heads. I have seen some YouTube videos of people putting the Ford Racing PI intake on a car with NPI heads and using RTV sealant to deal with the port mismatch with NPI heads. What does everyone think of doing that? Good idea or should I just stick with an NPI intake?
 
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98GTAZ

98GTAZ

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Here’s a picture of where the smoke was rising from. Right between the black square and silver IAC part, wafting up from the intake runners below.
 

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07GtS197

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If money is no object, I’d get a new Ford intake. Those aftermarket intakes are junk. It isn’t a direct bolt on but it’s worth it imo.
 

lwarrior1016

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This is a really good write up about the intake swap. You’d need the intake, valley coolant tube, alternator bracket, and tap the crossover for the second sensor. Not a bad job.
 
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98GTAZ

98GTAZ

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It seems the FRPP PI intake is out of stock everywhere. Soonest available is 1/23/23 according to most sites. I can’t eait until late January to fix this issue.

Likewise, all the yards in Phoenix don’t have any 99-04 GTs to pull parts off (they have a million V6s).

Is the intake on a 1999 or later Crown Vic, Towm Car, or Marquis a PI intake that will work? What about trucks with the 4.6?
 

lwarrior1016

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The Vic’s, marquis, town car, all those will work but they got pi in 2001 I think. The trucks are not the same, they have a huge aluminum intake.
 
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98GTAZ

98GTAZ

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So I found what I think is a Ford PI intake. I attached pictures. From what I know, I believe it is a PI intake since it came off a 1999 New Edge Mustang (door sticker said car manufactured 3/99). The first runner goes to driver side and the engine had the oil fill on passenger side.

Weird thing is it has two threaded holes for coolant temp sensors. I thought PI intakes only had one. However, there was a 2003 Mustang with a Dorman intake which I pulled off to compare, and the intake I got has longer wider runners and the coolant tube was for a PI intake. Any details anyone can provide on the intake I got today is appreciated (see pics)
 

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96blak54

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Yes, aftermarket indeed. Probably a Dorman. Definitely not a Ford.

Dorman doesnt sell a junk product. I have yet to hear about problems with their quality, yours could make it the 1st one. They are a good replacement product. Their downside is horsepower loss and mam oh man does it kill it!
 

96blak54

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Here is what a pre-finished ford pi intake looks like. Its one solid injected plastic piece. The Dorman is comprised of a few pieces and then sonic welded together to create a full intake.

Swapping to one of these will gain you roughly 15hp over a stock ford npi intake. Probably a good 25hp over the dorman. The swap onto npi heads is not a direct fit and is a process to achieve good results. Many many many people have made the swap with great success and is not difficult at all. Usually requires a few days mostly due to silicone curing time. If you make the swap, be sure to get specific felpro intake manifold gaskets.

20221029_030257.jpg
 

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waynenorcross

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It seems the FRPP PI intake is out of stock everywhere. Soonest available is 1/23/23 according to most sites. I can’t eait until late January to fix this issue.

Likewise, all the yards in Phoenix don’t have any 99-04 GTs to pull parts off (they have a million V6s).

Is the intake on a 1999 or later Crown Vic, Towm Car, or Marquis a PI intake that will work? What about trucks with the 4.6?
Try Jim at Performancepartsinc.com. tell him Wayne sent you. He carries a lot of odds and ends not on his website and has connections back at Ford.
 
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98GTAZ

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Since I could not find a PI intake, I decided to replace all the vacuum lines and the O2 sensors just to see if it would help.

Replaced both pre-cat sensors and every vacuum line except the purge valve to charcoal canister line ( goes into fender well).

It actually helped a lot. In particular the purge solenoid to purge valve had a crack in it. Not a complete hole, but cracked to inner lining. After doing that, the car ran better, but not perfect.

Seems to have its power back mostly. Still idles very rough. Idle has a chug-chug quality to it. Car shakes at idle.

STFT numbers changed too:
After initial warm up (car idling):

STFT B1: -7% to 0%
STFT B2: -2.3% to 2.3%

After a long drive ( car idling):
STFT B1: -3.9% to 1.6%
STFT B2: -3.9% to 2.3

When put back in gear after idling after long drive, B1 goes lean to -7% but recovers to -3.1% to 3.1%

At highway speed both banks seem normal at -3.9 to 3.9%

Idle is still very rough however. Also exhaust sounds off. Car has a Flowmaster cat back. Doesn’t have the distinct Flowmaster sound. Sounds harsher and more percussive almost booming.

The vacuum line from the purge solenoid to the canister looks pretty rough so I am going to replace it this weekend. I might just teplace the purge valve, solenoid, canister, and lines while I’m in there.

Any suggestions on the very rough idle will help.
 

SnakeBit!

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Assume you tried cleaning the IAC and have checked the hose leading from it as well as the little silencer box for cracks.
 

jfisher

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Yes, aftermarket indeed. Probably a Dorman. Definitely not a Ford.

Dorman doesnt sell a junk product. I have yet to hear about problems with their quality, yours could make it the 1st one. They are a good replacement product. Their downside is horsepower loss and mam oh man does it kill it!

I think you are the first one that I've ever heard that has NOT had bad luck with Dorman parts. In my experience they are absolute garbage.

Regardless, OP, have you checked fuel pressure? After reading your initial post the first thing that came to mind was fuel pump. Your car has that stupid variable voltage fuel pump like mine does and mine had a lot of the same symptoms when my fuel pump started taking a dump on me. The car trying to add fuel with the high STFT's tells me it's not getting the fuel it's commanding. I chased "vacuum leak" after "vacuum leak" (which the car did have), but it still never idled or ran correctly until I put a new pump in it. The current lean condition also tells me the same thing. I would check fuel pressure and if you find it's low at any point I'd replace the pump and have the variable voltage functionality either turned off in a tune or bypass the wiring.
 
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98GTAZ

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Checked the fuel pressure. It read 30 PSI which is the low end for the range for a 1998 with a return fuel system like mine. 30-40 is apparently normal per Haynes, and mine consistently read at 30 PSI. Held pressure after turning off car for longer than the five minutes Haynes said it should.

I went ahead and replaced the purge sensor, valve/solenoid, and all the lines between each component and the line down to the canister. That seemed to help quite a bit. STFT B1 was in the normal range at -1.6% to +2.3% and STFT B2 was at -2.3% to +2.3%.

That held for a day or two, but now the car is running rich. STFT B1 is constantly -6.3% to 0% and STFT B2 is -3.1% to +2.3%. It seems to mainly be running rich on B1, but B2 can sometimes dip to -6.3% before returning to a more normal range.

I am stumped. Not sure why it would run lean, than run rich. My code reader can read the extended Ford specific data stream and it reports that all of the heated oxygen sensors still read lean despite the rich condition on B1 from the OBD2 data.

Any suggestions are appreciated as this issue is driving me crazy!
 
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98GTAZ

98GTAZ

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So, I think this issue is solved. The car started throwing a misfire code (PO304 - cylinder 4 - Bank 1). I pulled the plugs on B1. Cylinder four showed signs of running very rich. The others looked lean. All the plugs on B2 looked lean.

I cleared the code and it came right back (PO304). I pulled the plug wires and tested them. The wires on B1 had high resistance that was 3 times the wires on B2. The secondary resistance on the coils was also out of spec.

I replaced the coils, wires, and plugs. Initially the car still ran super lean (STFT B1 at 24%) and threw a PO304 for a day. However after some highway driving the code cleared itself and the STFT came down to normal spec.

Since then, no misfire codes and STFT runs -3.1% to +3.1% on both banks. It will vary somewhat going as high as +3.9 to +4.7% and as low as -3.9%. Car is running a lot better, idles smoothly, and accelerates normally with the same power as it had before all of this started.

It seems like it must have been a combo of some bad vacuum lines in the canister purge system and bad coils and plugs.
 

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