Poor idle, NO power

[JW]

2003 4.6L has a bad idle and barely enough power to crawl down the street.

- Fuel pressure is 65 PSI
- Tested several injectors and got 12-14 ohms
- Tested several coils and got resistance across the terminals of about 0.5 ohms
- Tested the TPS and it seems to be fine
- Tested the MAF based on a thread from 2000StreetRod. The specs don't match, but the existing MAF is comparable to a remanufactured replacement. MAF has been cleaned.
- Plugs are brand new NGK iridium and show a light gray color.
- No apparent vacuum leaks. Manifold bolts are tight.

History: the long block in the truck is new. I replaced it because the old one exhibited the issues I'm seeing now, and I also had bad oil pressure on an aftermarket gauge. Carryover items from the old engine include a Trick Flow intake manifold and throttle body. The combo ran great for about four months prior to drastically losing power. Power output gets worse as the engine reaches operating temp. No overheating. EGR is not currently connected (needs to be modified, as the tube interferes with the upper plenum on the Trick Flow), so I do get a code for that. Feels like it's misfiring but no misfires are being recorded. If I slowly open/close the throttle, it will continue to run, albeit poorly. If I get on and off it fast, it'll rise up and then stall. When I experienced the original issue, it had run great up until it didn't; the loss of power was very sudden.

I have codes for the EGR, of course, and also saw some from when I disconnected an injector and a coil to try and trigger a misfire code (which it didn't, oddly enough). I also had codes for primary and secondary fuel pump circuits, which I'm trying to replicate (I started it without the fuel pump relay once, so that may have been the cause). I cleared the codes and am letting it idle now to see what comes up.

Additional testing - in park, throttle completely to the floor, I can't get over 1500 RPM.

 

[2000StreetRod]

I had a similar problem on my V6 when the common ground wire for the injectors on one bank was open. It was difficult to find because the PCM assumed that the O2 sensor on that bank had failed and used the O2 sensor on the good bank. I suggest making sure fuel is getting to both banks and the injectors on both banks are pulsing.

 

[JW]

Sorry, not sure how to go about doing that. I know about the screwdriver trick to listen for injector pulses, but today I can't even get the truck to run long enough to do that. It's slowly deteriorating. And still no codes. I've considered the possibility of plugged cats but can't figure out how that could happen suddenly.

Would a bad pump or filter still allow proper fuel pressure, but not enough flow to properly feed the engine?

 

[JW]

Update...

Replaced the fuel filter, because I had one and in 178K miles, it hadn't been done. No change.

Currently, the down pipes to the upstream cats are disconnected, and it runs great but won't idle. I'm going to remove the (brand new) IAC and clean it when it cools off.

 

[2000StreetRod]

Before it wouldn't run above 1,500 rpm. Now you state it runs great but won't idle. To me that's quite a change. Was it because of replacing the fuel filter or disconnecting the down pipes? A bad IAC valve won't result in no power - just poor idle control. Engine idle is degraded when there are only exhaust manifolds connected.

 

[JW]

I tested after the filter replacement and had no change at all. With the down pipes disconnected, it runs really smooth but struggles to hold idle speed. I figured that could be the IAC or that it needs a tune (new engine has different cams in it, but nothing radical). Hearing that disconnected exhaust may result in poor idle adds to the possibilities there. It revs freely now, where before it felt like something was choking the life out of it.

 

[2000StreetRod]

Apparently there is an exhaust restriction. I suggest a visual inspection of the tailpipe (and tip if there is one) for dents or collapsed bends. Also check for something stuck in the tailpipe that could block airflow. Since the downpipes are disconnected from the exhaust manifolds you might try blowing air thru the exhaust system. You might be able to adapt a leaf blower.

 

[JW]

That's a good idea. We'll rig something up for that.

 

[JW]

OK, apparently it's not the exhaust. It's still way down on power. Idle is sometimes better but still not drivable. What else should I be looking for? I'm about ready to put the stock TB and manifold back on, as it was the last change (albeit three months before the issues started).

 

[2000StreetRod]

There are a lot of possibilities and I don't know your actual configuration. Are you using the stock MAF sensor or did you install a higher flow unit? Since the engine will now idle did you try listening for injector pulsing? I've had luck on my engine using a length of flexible hose with one end near an injector and the other near my ear. You posted that the engine loses power as the operating temperature increases. Do you have any way to determine if the AFR is lean or rich? Is there black smoke exiting the exhaust pipe? Have you performed a compression test? Have you examined the condition of the new plugs since they were installed? According to my 2003 wiring diagrams the cylinder head temperature sensor provides data to the PCM that passes the data to the instrument cluster microprocessor. Do the instrument cluster engine temperature readings seem reasonable?

 

[JW]

Current, complete configuration is below.

Are you using the stock MAF sensor or did you install a higher flow unit?
Stock

Since the engine will now idle did you try listening for injector pulsing? I've had luck on my engine using a length of flexible hose with one end near an injector and the other near my ear.
Not yet but I will

You posted that the engine loses power as the operating temperature increases. Do you have any way to determine if the AFR is lean or rich? Is there black smoke exiting the exhaust pipe?
No black smoke. Exhaust smells as it should. I don't believe I have a way to check AFR (I don't have a separate gauge or wideband O2s; my OBD scanner has some logging capabilities but I haven't messed with it yet).

Have you performed a compression test?
Not specifically, as this engine/config is exhibiting the same issue as the previous one.

Have you examined the condition of the new plugs since they were installed?
Not all of them, but the ones I have looked at are light gray and dry (I've examined at least one from each bank).

According to my 2003 wiring diagrams the cylinder head temperature sensor provides data to the PCM that passes the data to the instrument cluster microprocessor. Do the instrument cluster engine temperature readings seem reasonable?
Yes; no signs of overheating at all, though I suppose if I pushed it harder (and it's running really lean), it would probably overheat.

Short Block:
Block - Stock Romeo aluminum, 0.020" over
Crank - Stock Romeo 6 bolt
Main bearings - Clevite
Main bolts - ARP
Side bolts - ARP
Rods - MMR I-beam/ARP bolts
Rod bearings - Clevite
Pistons - Manley/MMR
Rings - Total Seal
Oil pump - Hurricane (MMR)
Front main seal - Fel-Pro stock replacement
Rear main seal -MMR billet housing

Long Block:
Heads - PI, MMR Stage 2 ported
Head bolts - Fel-Pro stock replacement
Head gaskets - Fel-Pro stock replacement
Camshafts - Comp XE262H
Valves - Stock
Springs - Manley
Rockers - Stock
Lash adjusters - Stock
Cam sprockets - Melling
Cam timing - Straight up, matched side to side
Crank sprocket - Stock
Timing chains, guides, tensioners - Cloyes stock replacement
Reluctor wheel - MMR billet

Top End/Ancillary:
Intake manifold - Trick Flow Street Burner
Throttle body - Trick Flow 75mm
Injectors - Stock 19 lb/hr
Ignition - Stock
Spark Plugs - NGK Iridium 7164, 0.056" gap
Air intake - K&N cone, custom intake tube
MAF - Stock
Exhaust manifolds - JBA headers
Exhaust system - Stock
Fan - Ford Thunderbird OEM Electric, Flex-A-Lite controller
Water pump - MMR Performance
Pulleys - Steeda underdrive, stock alternator pulley

 

[JW]

If I understand the throttle position sensor test properly, I should see 5 volts in, and from 1 to 5 volts out depending on throttle position, with a pretty linear progression as the throttle is opened. Is that correct?

 

[2000StreetRod]

If I understand the throttle position sensor test properly, I should see 5 volts in, and from 1 to 5 volts out depending on throttle position, with a pretty linear progression as the throttle is opened. Is that correct?

Yes, although the range will probably only be from about 1 volt to about 4.7 volts.

 

[2000StreetRod]

My point on the engine temperature displayed on the instrument cluster was not about overheating. The PCM varies the AFR based on the engine temperature - rich for a cold engine and normal for a warm engine. If the gauge shows cool when the engine is cold started and normal when the engine has had time to warm up then the engine temperature is probably not an issue.

 

[2000StreetRod]

As I recall, Ford enabled the rev limiter in Park and Neutral around 2001. I think the limit is 3,000 rpm but that is well above the 1,500 at WOT that you experienced according to your first post.

Since you have a custom engine configuration I suggest a compression test of at least one cylinder in each bank. That will build confidence in camshaft timing, valve functionality and head gasket integrity. Make sure the throttle plate is wide open for the test.

Some tuners encourage a custom tune when the throttle body diameter is changed significantly. However, it is my opinion that your loss of power is not attributable to the increased throttle body diameter.

I'm not familiar with your camshaft specifications but if the changes are mild compared to stock the idle would be slightly uneven but acceptable.

In my opinion the stock 4.6L alternator output capability is marginal. I think it is only 100 amps. If you have an underdrive crank pulley and a stock alternator pulley then the available output will be decreased. What is the start up draw of the T-bird electric cooling fan motor? Does the Flex-A-Lite controller provide a soft start? I suggest monitoring the battery voltage when the fan starts rotating. If the voltage drops excessively the PCM and the ignition voltage may be adversely impacted. This could be an explanation of why the engine loses power when the engine is warm and the fan starts running.

 

[JW]

Thanks for continuing to check in. Let me fill in some gaps.

- The fan and underdrive pulleys have been in for close to five years. The controller does seem to have a soft start, though I don't know offhand what the current draw of the fan is (I followed JoshMcMadMac's install thread and used the same parts). I don't see a voltage drop when the fan engages.
- Alternator and battery are six months old.
- Intake and throttle body are about nine months old. I had a really good three month run with the combo installed.
- The power output issue is exactly the same as it was with the old engine, which leads me to believe something that carried over is the culprit. All of the electronics transferred over - sensors, injectors, coils - as well as the rails, upgraded intake and throttle body, everything beyond the new long block. Idle is more erratic, but that could simply be the camshafts being thrown into the mix.
- The power loss was immediate and drastic. It mimicked the performance/behavior of the original engine when it lost oil pressure, and I had signs of bad oil pressure with the previous engine after it lost power, which is why I went in the direction I did (and built an engine I would have built within a couple of years anyway).

I'll do a compression check this weekend. I did get to see the front of the engine before the cover went on, and the cams/timing gear all seem to be correct, but a compression check will rule that and many other things out. I also have a new Motorcraft TPS on the way, as what I've read suggests a bad one can cause a whole host of issues. The current one *tested* good, but it's a cheap experiment.

 

[boominXplorer]

I'm thinking the MAF is reading off. Do you have a scanner to bring up the stft and ltft (fuel trims)

 

[Turdle]

If you have a vacuum gauge, I would suggest checking idle vacuum.

If the gauge is not steady post a video of it with audio please.

 

[JW]

My scanner does do long and short term fuel trims. But I don't know what they mean. I can post what I'm seeing, though.

I did put in a different (non-Motorcraft, FWIW) MAF and got no change as a result. That went back to the store.

I need to get a vacuum gauge as well.

 

[JW]

Update: She's home.

Since completing the engine install, I've only made two changes - I tweaked the idle adjustment screw on the TrickFlow throttle body, and I replaced one vacuum line (no apparent splits or anything, but the very end of it was starting to go). That's it.

Idle is rock solid. Vacuum is a little low at idle (14-15) but perks right up above 1000 RPM. It struggles a bit over 2500 RPM or so, but I suspect that's a tuning issue (it's probably leaning out). I ran graphs for the upstream O2 sensors and short term fuel trims but don't really know what I'm looking at. The O2s varied between 0 and 1 volt and the fuel trims were between roughly -5 and +5%. Again, I have no idea what any of that means.

Current plan is to wait for my SCT iTSX to arrive from Unleashed Tuning and get that uploaded. Then we'll see how it goes.