Long Term Fuel Trims Significantly Different Between Banks

[jon_s_brady]

I've been fighting issues since I re-built the engine. I've got an extremely rough idle and the engine will sometimes cut out if I have driven for a while and then stop and try and reverse into a parking spot.

I'm reviewing my PCM/PID data using Torque. I can't see any odd numbers except that the LTFT on Bank 1 is always much higher than Bank 2. It goes up to 20% on Bank 1 after it idles for a while and eventually starts the CEL flashing warning of catalytic converter damage.

The LTFT on Bank 1 appears to be vacuum related. At idle the LTFT is high (>15%) and will go down immediately I accelterate or move at speed. This leads me to conclude vacuum leak issues but I've checked all hoses, replaced the bolts holding the intake manifold to the heads as well as the gaskets. I've also replaced the EGR and done a propane test around the engine with no result.

So I'm wondering if anyone has encountered issues with the LTFT being radically different between banks on a V6 or V8.

 

[JoshMcMadMac]

Injector o-rings? There are a litany of things that it could be, though.

 

[jon_s_brady]

Injector O-Rings...I had replaced them as part of the engine re-build. I've also got 39-41 PSI Fuel Rail Pressure (Relative to intake Manifold) so I would expect an air gap in the O-rings to see fuel pumped out.

That said, I'd be interested to see your list of possibles because I'm flat out of thoughts at this point.

 

[BobRob]

This SCREAMS vacuum leak. Which engine?

 

[jon_s_brady]

I agree, everything is pointing to a vacuum leak. The question is...where?
Aside from the LTFT the engine idles extremely roughly which I put down to it fighting to try to find the right AFR

I have:
Replaced intake manifold (IM) gaskets
Replaced IM bolts (have rubber components that appear to crush over time)
Removed PCV hose to back driver side of IM and blocked port - no change to engine performance
Removed each hose connected to the IM and blocked it's port to remove any vacuum leak - no change to engine performance
Replaced EGR - no change to engine performance

The thing I find strange is that if it was a vacuum leak involving the IM the effect should be seen in both banks. Since the high LTFT issue is tied to Bank 1, it would make sense that any leak would be beyond the IM since it is common to both banks.

I'm wondering what types of things could result in a vacuum leak in the head only. These heads had overheated and warped. I took them to a machine shop for re-surfacing. I'm wondering if there was/is a crack in the head somewhere.

 

[BobRob]

Any chance the cam timing is off?

 

[jon_s_brady]

The thing with this model of engine is that you need to buy the special timing tool for it. OTC 6488 Ford SOHC 4.0L V6 Cam Service Kit.

I bought that and don't see how I could have screwed that up...the camshaft braces holds the cam at TDC. You use the special chain tensioner to keep the chain tight while you tighten the sprocket bolt and the sproket is held in place with another clamp. So long as you have the crankshaft set at TDC it's pretty much foolproof. That said, I've always been troubled by what I hear as a tapping noise that I can here in the intake manifold using a stethoscope. Perhaps it's the valves although I do wonder if it's the valve lifters.

 

[BobRob]

From what I have read, it is possible to set either cam 180 degrees out of time even using the kit. There is a tab on the drivers side and a flat spot on the passengers side cam that is supposed to be facing up when you install the tool. I haven't done the job myself but have researched it extensively. There's a video on youtube where a guy doing the job explains how the cams have to be set prior to installing the tools.

Might be worth looking into.

 

[jon_s_brady]

The good part about using the tool is that the camshaft bracing tool can't be installed with the camshaft 180 degrees out. The offset slot requires the camshaft's slot to be in the correct location for the brace's ridge to insert into the slot.

 

[BobRob]

The good part about using the tool is that the camshaft bracing tool can't be installed with the camshaft 180 degrees out. The offset slot requires the camshaft's slot to be in the correct location for the brace's ridge to insert into the slot.

I see.. I'll go look at that a little later. I may have misunderstood the guy.

 

[jon_s_brady]

Oh, and I neglected to mention this earlier...

The only DTCs I'm getting are for misfires. P0300, P0304 and P0306 at the moment. Eventually I know from previous monitoring that I'll also get P0305, P0301. Interestingly I've never had a P0302...

The main point of this is that I'm not throwing P0171 or P0174 codes for a lean AFR. Indeed I'm not throwing ANY other codes than the misfires.

 

[jon_s_brady]

Still working on this. I've summarized everything that's been done to date. Anyone see something I've missed?

Initial Issue: Engine overheated – warped heads.
• Removed engine and stripped it down. Took heads and block to machine shop for block decking and head re-surfacing.
• Took transmission to shop for re-build at same time.
• Re-built engine replacing rings, valve seals, all gaskets and seals.
• Replaced fuel filter.
• Engine ran roughly and threw misfire DTCs (P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0316).
• Fuel trims were off. STFT1 and STFT2 appeared normal. LTFT2 was also around +/- 4%. LTFT1 was always around +15 - 20% at idle. Total misfire count rose rapidly at idle. When driving or engine above 1800 RPM the misfire count stopped and the LTFT1 dropped to around +10%. As soon as the RPM dropped the LTFT1 rose again to +20% and total misfire account started rising again.
• Replaced O2 Sensor #1 on both banks.
• Replaced intake manifold seals.
• Replaced EGR on intake manifold.
• Checked for vacuum leaks with carb cleaner – found none. Manifold vacuum measured by ECU is around 11 in Hg at idle.
• Since issue only related to Bank 1 on a V6 replaced that head with re-manufactured head.
• Re-timed engine with OTC 6488 tool kit.
• Replaced coil block, plug wires and plugs. No change to symptoms.
• Zeroized KAM to re-learn fuel trim. (disconnected battery’s negative lead and then connected negative lead to positive terminal for 15 mins)
• Replaced fuel injector adapters in heads.
• Replaced fuel injector seals.
• Checked resistance of all fuel injectors – 12.2-12.3 ohms for all.
• Switched all fuel injectors from Bank1 to Bank 2 and vice versa to see if problem lay in fuel injector flow rate/blockage – no change to symptoms.
• Noticed the Bank 1 O2Sensor #1 is bouncing between 0.1v and 0.6v.
• Engine continues to idle roughly with elevated LTFT1. When idling more than a few minutes CEL has started flashing to indicate possible cat damaging condition.

 

[fritz24]

Check the condition of your spark plug-this will tell what is actually happening inside the cylinder. You have a rebuilt engine, did u check the compression on every cylinder? It could be a head gasket issue or loss of compression-leaking exhaust valve that is dumping unburned air/fuel to exhaust system fooling O2 sensor. Also double check your wire make sure they are in correct firing order. As they mentioned earlier try checking the camshaft timing its also a possibility.

 

[jon_s_brady]

Fritz, thanks for the response.

Check the condition of your spark plug-this will tell what is actually happening inside the cylinder. No oddiscoloration or carbon build up on any plugs.

You have a rebuilt engine, did u check the compression on every cylinder? All within about 20% of each other

It could be a head gasket issue or loss of compression-leaking exhaust valve that is dumping unburned air/fuel to exhaust system fooling O2 sensor. Replaced head with professionally re-built head and gasket with no change to symptoms

Also double check your wire make sure they are in correct firing order. Done, they were correct

As they mentioned earlier try checking the camshaft timing its also a possibility.Used the OTC6488 tool specifically for the job to ensure this wasn't an issue.

 

[2000StreetRod]

Smoke test

I suggest performing a smoke test which in my opinion is the only reliable method to detect a vacuum leak.

 

[fritz24]

Verify the fuel system holds pressure with koer and koeo for 60 seconds.
Check the evap canister purge valve for leak or contamination.
If this still check out good, check for correct PCM operation.
disconnect all pcm connector.
Visually inspect pushed out pins and corrosion
connect all pcm connectors and make sure they seat correctly
carry out pcm selftest and verify the concern is still present.

 

[fritz24]

I forgot to ask. Compression test is 20%? What is the actual value you are getting? Is it within specs? Have you verified it with a leakdown test?
When the car is idling if you increase rpm does the engine smooth out. If it shake really bad while increasing rpm the problem would be at your rebuilt engine.
-check if you have a proper ground connection to your engine block.

 

[HOOAH]

I have experienced the same issues, Long Term fuel trim bank 1 was -13% while bank 2 was 25%. Both Short Term fuel trims were 4.8%. My fuel rail pressure was at 38 psi.

 

[craigssvt]

I have experienced the same issues, Long Term fuel trim bank 1 was -13% while bank 2 was 25%. Both Short Term fuel trims were 4.8%. My fuel rail pressure was at 38 psi.

Did you ever figure it out?

 

[08EddieCA]

I second the smoke test idea = chain smokin Grandpa and a 3/8 hose into intake manifold.