It was a typo, I meant MAF.
And yeah at this point it looks like I have no other choice than to repull the timing cover. Like I said its transverse mounted and in a cramped bay so itās a miserable experience. I even had to make custom tools to do it, because of its proximity to the inner frame and suspension.
Engines generally use the MAF or the MAP. Does yours use an MAP? If so, the purpose of that part is similar to the purpose of the MAF, to control fuel/air mixture. So itās good idea to at least test that part to make sure it holds vacuum.
At 15-16" the manifold vacuum is abnormally low. This means a clogged exhaust, cam timing off, or a worn out engine.
Gasoline diluted motor oil will wear out an engine quickly.
An exhaust restriction will cause the fuel system to run rich. Remove the upstream oxygen sensor from the manifold or pipe and see if it runs normal.
@ok4450 Incorrect. Where I live 17-21 inches of mercury is the normal range as we are 1200 feet above sea level.
@George_San_Jose1 MAP is only for off idle operation. Again this engine uses data from several sensors to calculate mixture. It has no MAF.
@Nevada_545 Correct. However not -34 worth of rich. If itās that restricted, that it would cause such a large amount of restriction (say a clogged cat) then just opening the oxygen sensor port would not move enough air. Itās easier to use the vacuum gauge already hooked up to test for exhaust restriction.
Yes, use the vacuum gauge. If the exhaust is restricted, with the oxygen sensor removed the vacuum values should return to normal.
I will, or run an open primary pipe test. However first priority is any possible timing problems. I just pulled the valve cover (all I had time for today before work) and checked lash. Two rockers were ālooseā when proper lash was set. I had to pull the valve cover anyway for later.
If Iām going to pull that accursed cover off again, I want to make sure itās on tdc in the bore and the valves mechanically. Overkill as tdc doesnāt really matter in this instance, but I like to be anal. And now, with the loose rockers I might have a worn lobe or two as well. The guy I bought the car from (family friend) put new lifters in around 90k after a valve job, so worn lobes wouldnāt exactly be a shocker.
The no power on load and the timing jumping around like it is, like others have rightfully said is probably something timing related. Perhaps the new tensioner failed despite being GMās best, or I have it a tooth off. Either way I think diagnosing the timing at this point is the best direction for now.
Are you sure about that? Hereās what it says in the service data about rich operation, these are the sensors used that will flag a p0172 code (overly rich). If your point is that it probably isnāt the MAP sensor, thatās likely true. We see very few complaints about failed MAP sensors here. But if it is the MAP sensor, nothing you do with any other system in the car will fix the problem.
Intake Air Temperature (IAT) Engine Coolant Temperature (ECT) , Engine speed, Vehicle speed, Manifold Absolute Pressure (MAP), BARO, Evaporative Emission (EVAP) purge, TPS
Iāve been very busy as of late, but I still work on the car a bit every day after I come home from the gym. I just need to unbolt the timing cover, and make sure tdc is set, and Iāll know (also for anyone still following this) if I screwed up installing the timing chain and tensioner. Heading out there now.
I bought a 24", 1/2" ratchet just to make the balancer hub, crank bolt, and pulley easier to pull. 36$ and worth every single penny. Thanks, Tekton!
Alright, Iām a tad confused here.
Here is the old camshaft gear. Iāve always heard that when timing is properly aligned the cam key slot should be at 6 'oclock, and the crankshaft keyway should be at 12 oāclock. So this picture is for reference to the following.
Here is the current alignment at compression TDC. Crank gear dot lined up with tensioner tang correctly. Camshaft dot at 12 'oclock. Camshaft key slot at 9 oāclock.
Here is the current alignment a rotation later at exhaust TDC. Crank gear dot lined up with tensioner tang correctly. Camshaft dot lined up with crank dot. (although half a tooth off? pic in a minute) Camshaft slot at 4 'oclock.
Oh, and for anyone wondering how I determined TDC, I used an old mechanics trick I learned years ago, where you remove the Schrader valve from your compression tester, and stick your vacuum gauge on it. You can see on the gauge when the needle moves from holding pressure to 1 pound of vacuum, then you just back the crank off to 0 vacuum.
I donāt think soā¦looks āper the bookā to me. Iād double check valve rocker range-of-motion to eliminate the āworn cam lobesā possibility you mentioned before.
so you think it being on exhaust tdc and not compression tdc doesnt matter?
Well, when lined up per the book, youāll always be at Exhaust TDC, right?
Yep, just wanted someone to confirm Iām not crazy.
I also donāt think itās a 1/2 tooth off anymore. If you look at exactly https://youtu.be/BjyMBlArYcU?t=465 in the video, you can see his is the exact same position as mine.
So, Iām back to square one. Which is a vacuum leak of 3-5 inches, and live data that tells me the timing is swinging wildly. Plugs tell the same tale. Still sooty from rich condition, but since replacing the chain previous, the electrodes have white areas on the electrode, from too much advance. (Iām assuming)
Would worn cam lobes cause the wild swinging? Theirās only so many things left to cause a leak. Worn cam, head gasket, bent valve(s) from all that chain slop before, and restricted exhaust.
Thanks to all for the help, btw. Also bat signaling @asemaster as heās been helpful to my brother in a few posts now.
I donāt know that Iāve ever been much help to anyone and I donāt know who your brother is, but Iāll help if I can.
Your timing marks look fine.
Stating that sensor readings and fuel pressure are good or in spec doesnāt mean much. I would want actual values at idle and 2000 rpm. Do you have a live data scan tool capable of this?
Your engine vacuum is low, even for 1200 ft. But low vacuum and a STFT of -34 (or whatever it was) precludes a vacuum leak. If the car had a vacuum leak the ecm would add fuel, not take it away.
Whatās the vacuum gauge doing at idle, is it rock steady or is it fluctuating or pulsating?
You donāt mention if you ever opened up the O2 bung or header pipe to see if that made any improvement.
I donāt often do compression tests but at this point I would want compression readings on all 4 cylinders. Should be easy on this car.
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Have you checked the uniformity of valve opening (for worn cam lobes)?
Have you replaced the spark plug wires or coils?
I donāt have the pad I wrote all the diagnostic results on in front of me, but it was 45 at idle.
No, it proves it. The map thinks the car is under load, so more fuel gets dumped into the engine. The map is reading low vacuum from a leak, or there is a condition somewhere causing not enough vacuum to be created. Thatās technically not a āleakā, but the term is close enough. The rich fuel trim numbers show the engine trying to compensate for said load. I think youāre confusing fuel trim ā-ā with timing variations?
Vacuum gauge pulsates quickly .25 inches back and forth at idle. Rock steady on load. I did mention the port, actually.
Not yet. But itās The next order of business. I just ordered a dial gauge/cam checker. When it arrives Iāll check the cam lobes. I also get an excuse to buy a new tool, haha.
Plugs and wires were new, coils and ICM are new. Previous owner replaced them. And like I said, checked and in spec, with strong spark.