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I tested the intake for vacuum leaks and found none, so I think that was the last check. Everything seems good to go for a test drive shakedown from all the repairs I have done since putting the car up on stands in October.
In this repair cycle I have done the following:
Restore intake and cam cover new hoses and lines / knock and CPS sensors / new injectors
Install oil baffle and reseal oil filler neck + seals for dipstick and filler cap
Replace thermostat / coolant coolant flush / new coolant hoses.
The car was running awesome pulling strong straight to redline several times and then on the way home things starting going wrong.
The first symptom was a full motor cutout under load (second gear accelerating to 4k). I was able to repeat that a few times as I was returning home but the cutout was happening more and more at lower and lower RPMs. It was idling fine and i was able to limp home.
I pulled the airbox and installed my pressurizing device and found the intake was leaking air someplace.
I could hear it escaping someplace under the plenum. I was able to feel around the main boot and the two side ducks but was not able to feel the leak.
I suppose a smoke tester would be useful in finding the leaks but repairing them will require removing the intake either way. Im super bummed because everything else was working so nice.
Any thoughts on what is causing the cutout? I checked all the vacuum lines to the fuel pressure dampers and regulators. they all seem to be intact.
Did you inspect the condition of the wires of the MAF sub loom- especially under the boot and under the doubtless crispy fried heat shrink where it necks? Removing the connector and reinstating it might exacerbate any weakness and those wires [if original] could possibly be toast by now..
Also ensure the MAF connector is seated correctly. If still original, reworking that sub loom and fitting a new connector is no bad thing. I reworked mine a few years ago using the original connector and everything is still working fine to the best of my knowledge but the conductor insulation under the boot was a shambles. Cutting back and inspecting under the heat shrink is no bad thing either and that will doubtless be carbonised by now if still original.
Apologies if I missed anything earlier in your thread.
Did you inspect the wires of the MAF under the boot and the connector
Interesting, I did a high level inspection, noted the boot was cracked and repaired it with liquid electrical tape. But I didn't do a through job peaking under the boot. I suppose I could I could do better and take a second look. It would mean destroying my repair job. Do you know if the connector and boot is available? I did a quick search in the WSM and found some tests for the harness in Manual Volume 1A, Page D 24 - 15 and this handy diagram
I am curious why you think the issue is MAF related? I can tell you my MAF was rebuilt about 10K miles ago.
Last edited by Michael Benno; 02-07-2019 at 11:59 AM.
The MAF connector and boot are available separately from Roger, along with replacement pins if you need them. Else the pins are removable from the connector housing to get them through the boot.
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My sole issue with the MAF connection was a few years ago, when I found some wax-like deposits in the connector that were interfering with electrical paths. Wiring, boots, shell, etc were in great shape except for that. Symptom was very similar to "not enough fuel pressure", where the engine ran OK at low throttle position and load, but was starving for fuel if I tried to go more than maybe 30 MPH. There's a very good chance that the LH was actually in "limp mode". Happened just a couple miles from the house, so I was actually able to "limp" home. Rolling diagnosis on the way used the MPG reading. I tested fuel pressure first because it was fast and easy, then went to the MAF. Connector contamination was pretty obvious. I have no clue where the crud came from, as the boot and the connection were completely intact. It was last apart for a test/trial in another local car a couple years prior. It doesn't take much extra resistance an the low-current circuit to the MAF to mess things up.
Search for the airflow leak noise with a piece of vacuum hose attached to (ideally...) the inspection camera. Else a piece of stiff wire you can use to poke and listen under there. The other end of the hose goes into one ear, so you can listen 'locally' for the airflow at the other end.
I am curious why you think the issue is MAF related? I can tell you my MAF was rebuilt about 10K miles ago.
Michael,
The logic is simple- you may well have a vacuum leak of some kind but the chances of a major leak after an inlet off job must be pretty remote and even then, a vacuum leak is what it is and it is not likely to be a sporadic type of thing.
On the other hand your description of events sounds to me very much like a MAF load signal being corrupted- if the signal value is suddenly lost or reduced there will be much more air flow than there is fuel to support it and the motor will die. Quite feasible that the rocking motion of the engine in its mounts just may be enough to make the difference between a viable clean signal and a corrupted one. Then of course there is also the MAF itself - unlikely if the unit has been refreshed in recent times but until one knows what is the root cause of the problem, omitting obvious candidates without verification is often a monumental folly. At least the MAF can be tested or a known good unit popped into the car if available. At least I have the luxury of having spare MAFs and computers my my disposal and I also have ST2 to hook up that would show clearly if the MAF signal was taking a sudden dump.
The MAF connector boot, and pins are available from Roger.
Thanks for the tip Bob, I contacted Roger for the parts.
Originally Posted by FredR
Your description of events sounds like a MAF load signal being corrupted; if the signal value is suddenly lost or reduced there will be much more air flow than there is fuel to support it and the motor will die. Quite feasible that the rocking motion of the engine in its mounts just may be enough to make the difference between a viable clean signal and a corrupted one. Then of course there is also the MAF itself - unlikely if the unit has been refreshed in recent times but until one knows what is the root cause of the problem, omitting obvious candidates without verification is often a monumental folly. At least the MAF can be tested or a known good unit popped into the car if available. At least I have the luxury of having spare MAFs and computers my my disposal and I also have ST2 to hook up that would show clearly if the MAF signal was taking a sudden dump.
Fred, thank you for the explanation. This does make sense to me, much more so than a vacuum leak to to intake. I will remove the MAF and test the connections for continuity while wiggling the loom.
On the vacuum leak side, its a medium to small sized leak. When I charge the system with 5psi it takes about 5 seconds for the pressure to go to 0 psi. I was able to verify the main elbow from the MAF is secure so I don't have a gaping hole style leak.
Thanks again for helping to steer me in a plausible direction. Once I have the MAF off, that will give me better access to find the vacuum leak too.
I removed the MAF and gave the connecter a thurough inspection. I removed the torn boot to get a good look at the wires and they all look to be in very good condition as well as the connector. Nothing is in bad condition other than the boot.
I did a couple continuity tests on pins 3 (ground via LH) and pin 4 (ground) while moving the harnes wires and everything maintained connectivity. I still need to test pins 1, 2, and 5. But it was too cold tonight.
I tried to bench test the MAF but the only test I could find was a reference was for testing the resistance of hot wire circuit at the air mass sensor;
“(WSM) Disconnect the plug connection at the air mass sensor. Connect terminals 3 and 5 at the air mass sensor with the ohmmeter. Display: 3.8 - 4.10 ohms”
i did this test and saw infinite resistance. The hot wire looks unbroken. Just wondering if I did it wrong or if my MAF is FUBAR?
{EDIT} Im an idiot. I didnt have the correct lead plugged into the multimeter. You can see the correct red lead plugged in. DOH! Once I figured out my error I did a full complement of tests (see post below)
Are there other bench tests I can preform?
Lastly I verified the MAF was replaced with a refurbished unit in 2010 or 10,000 miles ago. It has the “Bosch refurbished” sticker on it. It was working fine before the intake refresh.
Last edited by Michael Benno; 02-09-2019 at 12:04 AM.
If the MAF was "sorted out" 10 years ago that is a fair amount of time for something in the circuitry to degrade. I see you are in Portland, Oregon- trust you are aware Louie is just down the road from you and I understand he can test your MAF for a small fee assuming he still offers this service as an agent for John Speake..
Chasing down an intermittent problem is really irksome as the conditions that induce such can be difficult to replicate but as variables are eliminated the closer one gets to the root cause. The wiring superficially looks to be in great shape but just remember that does not necessarily mean it is.
As a throwaway query, did you disturb and of the HT connections- specifically the spark plug and distributor cap connectors? A quick check to ensure they are all pushed home firmly will not go amiss.
If you are hooking up with Louie you might also consider checking out your LH. Although some LH failures are predictable some are atypical. Friend of mine had a problem wherein the car for a few minutes and then ground to a halt. I lent him my spare LH unit and the problem immediately disappeared.
01-28-2019, 03:13 AM
All systems are go for touchdown.
