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Sudden loss of power after valve cover gasket replacement/intake removal.
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afinepoint
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Jun 9, 2009, 2:32 PM
Post #1 of 21
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Sudden loss of power after valve cover gasket replacement/intake removal.
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Car is a 1999 Mazda 626 V6 2.5L with 137,000 miles.
I replaced the valve cover gaskets due to excessive oil leaks - mess on engine and exhaust manifold. This required removal of the intake manifold. The engine started and car ran fine for test drive of about one mile. I returned home restated and went back out. After about two miles the rpms dropped to near zero and the engine had no power. It could not climb a mild grade. No throttle response. Had to have towed home.
TPS OK and and power check to MAF OK. The engine will start but has a very low and rough idle like there is a massive vacuum leak or it is getting minimal fuel. It will stall after a minute or so. All hose are connected and there are no cracks. Wire and connector inspection looks good. No engine check light. All lights extinguish when the engine starts.
There is fuel pressure to the injectors. Hooked up a scan tool (Actron CP9180). No codes found.
One suggestion I received it that the timing belt skipped a few teeth. I pulled back timing belt cover and ran a boroscope inside. The belt is intact and dry and I can see no sign of damage. Rotated it one full turn viewing with scope and another with unaided eye. Can't see anything problems.
It is too coincidental that it wasn't something I touched I just can't find it.
Thanks,
Reg
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Loren Champlain Sr
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Jun 9, 2009, 3:18 PM
Post #2 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Sounds to me, that it is actually overfueling. Could be from a vacuum leak causing the computer to see a lean condition and compensating with fuel? When you mentioned intake manifold, you meant plenum?, right? If any coolant lines were breached, could have air in the cooling system which could affect the CTS reading, again causing a rich condition. If you connected the wrong vacuum line to the EGR, could be opening at the wrong time causing a massive vacuum leak.
The odds of the timing jumping during this process are slim, but if it backfired at any time, could happen in a heartbeat. Check cooling system to make sure it's full. Check CTS connection. Check vacuum source to EGR. Make sure you have no air leak between the MAF and the plenum. Make sure the MAF is plugged in. (BTDT).
Loren
SW Washington
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Guest
Anonymous Poster
Jun 9, 2009, 5:45 PM
Post #3 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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The entire intake manifold had to be removed to access the rear valve cover. Several hoses and sensors unplugged. I am sure I have reconnected all properly but . . .
What tells me I did is that the engine started and ran normally for a good distance.
No sound of air leakage. The only breach I have found is a large crack in the intake tube upstream of the MAF.
Will look at areas you mentioned. No backfiring occurred. Also plan to unplug and replug sensors in case of bad connection however again scanner saw nothing.
Thanks for reply.
Reg
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Sidom
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Jun 9, 2009, 5:59 PM
Post #4 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Also one thing you can check is the ground straps. I believe there are 2 or 3 grounds on the back side of the plenum, back by the firewall. Look back there & make sure they all got bolted back on to the plenum.
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Loren Champlain Sr
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Jun 10, 2009, 12:31 PM
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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In addition to Sidom and Hammer's replies, a vacuum leak can be masked while the engine is warming up as it is running rich. As the engine warms, the fuel is commanded leaner. I still don't understand why the intake manifold was removed? The plenum is bolted to the intake manifold. It should have been the only thing you had to remove? I think some manufacturers call it a purge tank?
Loren
SW Washington
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Guest
Anonymous Poster
Jun 10, 2009, 3:09 PM
Post #7 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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The only breach I have found is a large crack in the intake tube upstream of the MAF. If by "upstream" you mean between the sensor and the throttle body, then that could definitely be your problem. You can't have any unmetered air coming in, in that area or you will have a lean mixture.
No between the MAF and atmosphere. There are no other sensors upstream of the crack.
Reg
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afinepoint
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Jun 10, 2009, 3:14 PM
Post #9 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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All of the above "Guests" are me. Thought I was logged in.
I think we are still missing a valid point. Why did the engine start and run well for miles to begin with? Well after it had warmed. What sensor comes into play after the engine is hot?
Reg
(This post was edited by afinepoint on Jun 10, 2009, 3:19 PM)
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Sidom
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Jun 10, 2009, 5:55 PM
Post #11 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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You're taking the right steps, double checking everything you did. If the car ran fine before & now doesn't it would seem to be in the area you worked. No SES or codes pretty much tell you all the sensors are plugged in & no wires are pinched (I'm assuming you have a SES light on with the key on engine off).
With the no SES now you are looking at mechanical, fuel, air. stuff not computer controlled. If you drove it far enough you would probably get a rich bank, lean bank, cat code, etc. But you don't want to do that.
After you've triple checked your work, I would start looking at the basics. Pull the brk booster line off while it's running, if it idles up & runs better it's getting to much gas. Put a vacuum gauge on it & check your vacuum. If its low & shaky, it's possible your T belt jumped a tooth. After its warm if the vacuum is slightly low & steady @ idle & drops to almost nothing under load you might have a restricted exhaust. You could pop an O2 out when it's bogging & see if that helps...
I still think it's is something you are overlooking when you put it back together but it sure wouldn't be the 1st time something else on a car failed right after a repair was preformed correctly..... BTDT 
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afinepoint
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Jun 11, 2009, 2:06 PM
Post #12 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Went to start engine today and battery is discharged. Looks like I also have a ground which might be (part of) the problem.
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afinepoint
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Jun 12, 2009, 1:56 PM
Post #14 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Charged battery and trudged on. Started back at basics. Fuel + air + spark + rotation = running engine.
Starting with fuel I found I had no pressure at the rails and could not hear pump running. Fuel regulator relay tested good. Loosened gasoline fitting at rails. Turned key on - no fuel. Pulled pump relay and shorted connections - fuel spray. Looks like the relay is bad?
But while shorting the connections (with fitting tightened) the engine would not start. Sort of makes sense as I had pressure before and it would not start. 
Will pickup light for testing plugs cables for spark.
Reg
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Sidom
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Jun 13, 2009, 9:07 AM
Post #15 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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It's tough not being there. It really sounds like you've covered your work. I know the Mazda's are a little hard to test fuel pressure due to no port but a gauge would really help. The system will only power up for 2 sec with KOEO (key on engine off).
Going off what you saying, IF there is no fuel pressure and spark, all the grounds have been verified good (along with all the other basics). I would start looking at the Main relay & wiring. The Main feeds the control side of the fuel pump relay along with other systems.... You might want to get a good wiring diagram. Maybe Tom, Loren or Hammer could post one for ya....
But before you jump into this, here is the most important step........
Take a break....Walk away for a day or two... Sometimes when you get caught up in a problem child like this it is very easy to overlook something simple due to tunnel vision... Don't even think about this POS (it's a POS cuz of the problem right now...once you get it handled then it'll be a nice ride again) come back in a day or two with a clear mind & you nail it right off the bat.....
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afinepoint
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Jun 13, 2009, 12:53 PM
Post #16 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Thanks I appreciate the kind words.
I got another relay from the junkyard to use for testing purposes. Better than buying from the dealer. $2.75 vs $27.00.
After doing a dry run on the junkyard's I tested mine. Guess what mine is good. After a "Look at the sky, scratch head, ask WTF" moment I checked the fuse box side connectors and found an open in the ground circuit for the relay. Control circuit not pump circuit.
I don't know where the box wire reaches ground but if it joins others and thus there is a common ground then that may explain a lot. Something broke or vibrated loose.
More to come.
Reg
(This post was edited by afinepoint on Jun 13, 2009, 1:12 PM)
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afinepoint
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Jul 6, 2009, 12:41 AM
Post #17 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Need to find what makes turns on the fuel pump. One person responded that the PCM must see a spark signal to allow fuel. Where do I test for this signal? The spark plug wires themselves?
Each time I try to start the engine it sounds worst than before. It actually did a mild backfire yesterday.
Reg
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Hammer Time
Ultimate Carjunky
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Jul 6, 2009, 3:44 AM
Post #18 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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The trigger ground is how the computer controls the relay. It's simply not turning it on. This can be for any number of reasons. See if you have lost spark also. Check the power feed to the injectors from the ASD relay and see if first, it powers for 2 seconds with key on and then comes back on when cranking. It's common for these to lose a crank sensor and that will shut everything down.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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afinepoint
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Jul 8, 2009, 12:28 AM
Post #19 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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She got a spark and power to the injectors. Got a puff of smoke from below the MAF area on first start this morning and no smoke on second cranking.
I've run out of time on this one. She's being towed in today. Today's my last day off this week then I work 8 (4 12 hour and 4 8 hour days) with only one off in between.
Thanks for all the help. I really appreciated the assistance. Will post what the garage finds.
Moving on to my F350 with oscillating voltage, the 911's O2 sensor installation, shift bushing replacement and tune up and the wife's Camry with a host of needs. Actually the Camry's being replaced. I'm only one man.
Reg
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afinepoint
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Jul 13, 2009, 9:11 PM
Post #20 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Problem found.
The good news: the problem was found and equally important it has nothing to do with my work.
The bad news: It was the last place the garage looked and the last place I was starting to look before throwing in the towel.
Where you ask? For those who mentioned timing pat yourselves on the back. The timing was off five teeth.
The belt had not skipped because of oil on it but because the tensioner has failed. I incorrectly believed that a skipped belt would show damage. It won't if there's no tension on it. 
This will go down as the most expensive timing belt change for a non exotic car. The final bill? I can't bring myself to post it. Lets just say that for five times that I could buy another 626.
The moral of the story: approach a new problem as just that - new. The valve cover job became a distraction for a completely separate failure. The engine started and ran properly after my work thus that repair was done correctly. Things can break at any time whether thousands of miles or years after the last repair or the next minute and 100 feet out of the driveway. The last is so true. I did some work once on an Explorer I once owned. Afterward I went to start the engine and the starter died. Completely separate but we would all likely blame a repair shop had they done the former work. The shop manager for the garage doing work on the 626 says it happens all the time.
I learned something here about troubleshooting and perseverance. I hope there is something here for others to take away as well.
Thanks to all.
Reg
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Sidom
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Jul 14, 2009, 8:40 AM
Post #21 of 21
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Re: Sudden loss of power after valve cover gasket replacement/intake removal.
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Thanks for coming back & posting the fix......
Yes it's very easy to get "tunnel vision" on a certain area, especially right after a repair.. and a lot of the time, that is the area you need to be.... an old saying " A new problem??? Show me the last area to be worked on and that's where the new problem will be" It's unfortunate you ran out of time and I know you are hatin hindsight at this point.....
But I will say, good job on sticking with it for as long as you did and if you had a little more time you would've got there. I can tell from your posts that you have better than average repair & daig skills (probably better than some of the guys I work with  ), so thats a leg up over alot of people. Everyone has had a problem child like this & if they are tellin ya the haven't, then either they're lying or just working on gravy stuff & walking the hard diags....Some days you get the bear & other days the bear gets you....
It sux but at least you were able to take some important things away from this, so I won't call it a loss but a wash.
Good luck with the rest of your projects & don't be a stranger.........
(This post was edited by Sidom on Jul 14, 2009, 8:40 AM)
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