rt1970ls6

I recently had a bad rear center ignition coil and a leaking valve cover gasket. The car has about 140k miles, so I decided to do a complete valve cover gasket, plugs and ignition coil replacement while I had it apart. I removed the intake manifold, all ignition coils, both valve covers and all spark plugs. I replaced all plugs using anti-seize, replaced the valve cover gaskets and spark plug tube seals and all six (6) ignition coils. I insured I had everything connected correctly, vacuum hoses and all. I started the vehicle and it ran GREAT! in the garage. As I backed out, I noticed it took much more throttle pressure (motion) for the car to move. Low power. When in drive and giving it half throttle, it moved, but seemed to "bog" like it was getting no fuel. It would barely move the car, very low power. No missing, just low power. In neutral, it will only rev to about 3,000 - 3,500 and is bogging badly. At about 3,500, the rev limiter makes it miss badly.. I THINK (NOT going to say I KNOW, lol) I have everything connected correctly, but obviously I've overlooked something. The car's computer is not showing any codes at all. The scanner shows all good. I can't think of anything I did that should have caused this. I'm frustrated to ask for help. I'm a competent mechanic who has drag raced for years, but I need HELP!! LOL! Any suggestions??

ukrkoz

Well, didn't you just answer your question? Low fuel? You've been around fuel rails and fuel pressure regulator. Does not take much.

seemed to "bog" like it was getting no fuel.

As "maybe I'm lucky" measure, pull ECM fuse out for about 15 minutes.

rt1970ls6

Thank you, I'll try that tomorrow. However, although I was working near the fuel rails, injectors and fuel pressure regulator, I did not have any interaction with them. I did not unclip fuel injectors, open fuel fitting, touch the fuel pressure regulator or anything like that. I will try the ECM fuse first, but if that doesn't fix the problem, what did you mean by "Does not take much."? Is there something specific you are referring to that I am unaware? Please tell me what you know. I am baffled by this... But thanks for the input so far.....

salimshah

Did you replace gaskets of the sections you separated of the intake. Any introduction of unmetered air will upset the amount of fuel being injected.

Listen for hissing sound.


Salim

ukrkoz

What Salim said. Though I am not really sure how it will introduce more air as valve train areas are not really connected with air intake. Now, having a cracked vacuum line or hose, as the result of repair, though "re installed", surely can.
Does not take much. It is a very confined area to work in. Does not take much to incidentally push, move, or dislodge something. Also, from personal experience, does not take much to simply forget to connect something, or connect all the way, being in absolute confidence that it was all done right.
Do brake cleaner test for air leaks. Cheap and easy.

rt1970ls6

I removed the ECM fuse and disconnected the battery for 24 hours. I checked the intake for vacuum leaks and found none, but replaced the gaskets with new ones anyway. Still have the problem. Very low power, will not rev above 3,000-3,5000 rpm, "bogging" excessively. NO CODES at all on the computer. Originally, car ran fine except for an ignition miss (bad coil) on cylinder #3. Removed intake, replaced both valve cover gaskets and spark plug tube seals, replaced ALL spark plugs with new NGK platinum (used anti-seize on threads), replaced ALL ignition coils with new ones, replaced the top intake and gaskets. Re-fired the engine. Idles great. Revs in neutral to 1,500-2,000 rpm good at no load. put car in gear and it requires EXCESSIVE throttle motion to initiate motion. Car feels like it is bogging constantly when in gear. My guess: Either excessively retarded timing due to wiring/vacuum issues or no fuel delivery due to unknown cause. This was a simple repair to have gone soooo wrong. Help! Any ideas???

salimshah

Check the fuel connector again.
Check all ground straps that were disconnected.
24hrs is an overkill ,,, it just might be the time you took to verify other things.
Double triple check connectors.

Salim

rt1970ls6

Thanks for the comments. The 24 hours was just the time I had. Went by the shop, disconnected, came back next day, reconnected, replaced fuses, etc. I will check all connectors and grounds. I was sure to reconnect the TWO ground straps at the passenger side end of the intake plenum AND the ground strap at the rear of the plenum next to the difficult-to-connect brace. Are there others I overlooked/forgot? All other electrical connectors were reconnected properly to the best of my knowledge. I will re-check this afternoon.

Lexmus

I know you checked for codes, but did you check the fuel trims and other air and fuel parameters on your scanner? If not, do that ASAP after you do another recheck of your work.

rt1970ls6

Ok. Will do that this afternoon.......

rt1970ls6

The short term fuel trim for bank one and bank two were very erratic, making swings from -13 to +8 % +/-. They were NEVER consistent. Any ideas? Still no codes. I could not detect vacuum leaks with brake cleaner.

salimshah

Since one can not see, feel for an unhooked ground between the firewall and the engine,

Salim

rt1970ls6

I looked and felt for loose grounds or other wires and found none. I allowed the car to warm up to insure it was in closed loop control. The vehicle short term fuel trim stays between +3.5 and -3.2% on both banks from idle to about 1,900-2,000 rpm. The log term fuel trim is less than +/- 2.0%. The car seems to run ok in that range. At or about 2,000 rpm, +/-, the fuel trims, both short term and long term, drop to about -18 to -19% and the vehicle goes into a catastrophic bogging condition. However, there is still no computer codes. What would cause such a dramatic fuel trim swing?? Thanks!

Lexmus

Did you change any of the A/F sensors or the MAF? It sounds like the system is measuring a rich condition at the higher RPMs, but it is not actually rich, so you are short of fuel when the trims go strongly negative.

Monitor the MAF output as you rev the engine and see if the value changes abruptly when the trims drop. If the computer is sensing that the air flow drops, it will reduce the fuel to compensate, but it could just be a bad MAF. But I would expect the A/F sensors to pick up a lean condition. So I really think the issue more likely resides with the A/F sensors. If you can, also measure the A/F sensor and downstream O2 sensor output as the RPMs increase and report back.

2013FSport

iTrader: (2)

After disconnect the LTFT need to be relearned by driving but this really seems like an unmetered air leak. How long did sealant cure before it was started? Any chance it has an internal port leak pulling air there?

That said, where are the knock sensors on this engine and is it possible they were or wires to them disrupted?

What brand are the coils and plugs? And did you actaully check the gap on the new plugs?
Is this the second NEW set or ??? Yes our precious metal plugs are gapped at the factory but I would verify they meet spec.

After that; Install the 3 to 5 of the old coil packs and change nothing else! See what happens if MAF test is good.

I'd plot calculated load, RPM, MAF volume, and ignition advance. See what stands out.