Vacuum line runs cause low reading?

[NC280z]

I forgot to mention that I used a dual-gauge leakdown tester and that all cylinders were less than 20% on the gauge, which I'm told is where a good running or new engine should be at. Is there an easy way to tell if the cam is out of spec, causing my issues? I'm still tempted to put the exhaust back on and drive it a bit, but would driving it with such low vacuum cause any premature wear or damage?

[smoke]

Wouldn't hurt it any. Have you done a compression test? I don't remember if you said you did. The psi you have can tell you a lot.

[NC280z]

Used a Snap-On comp gauge, all cylinders read at around 140psi I believe, and all were within a few psi of each other. I did the compression test cold, however, so that reading might be (should be) higher warm, and probably will get better as I drive since it has exactly 0 road miles on it. The oil is also a bit diluted with gas, as the cold start/coolant temp wires got swapped accidentally, and the engine ran extremely rich for the first few runs.  When I installed the cam I did so per the FSM, lining up the bright links with the proper marks on the crank/cam pulley (#1 spot on the cam pulley) and the v-notch is just right of the cam tower mark at TDC, so I believe the cam is set up properly, although I didn't think to have my local machine shop check the cam to ensure it was ground properly by Delta.

 

Thanks again for all the great ideas, I've had this car and been working on it for 2 years (one of those years was an Afghan deployment), and now that everything is put back together my frustration is growing since I'm missing out on valuable clear-weather driving time, which is rare on the NC coast in spring/summer. BUT, I'm going to be patient, I just need advice from you Datsun gurus' as this is my first time rebuilding an engine. I've pestered my local machinist with a whole plethora of questions, but he's more of a SBC/SBF guy and not an import enthusiast, although I'm certain the principles are all the same or similar.

 

Oh, and to see/hear the engine running go to Youtube and search "280z new engine low vacuum at idle", I tried posting a link but it didn't work out so well. But, here it is anyways (youtu.be/lqEsJE9cKXs)

[smoke]

On the leak down, if it was close to 20%, that is quite a bit, even for a new engine, was ALL the air going past the rings? If so, put it together, take it out and run it hard, it might get a little better (or maybe even a lot). 

 

 

I'm not a Datsun/Nissan expert by any stretch of the imagination. Guys like Mike are however. Engines are just air pumps and operate on the same principles for the most part. That is more my "area".

[NC280z]

So I've reconnected the stock exhaust, set the base timing with the vac-advance disconnected, and attempted to take it for a drive. Right now it won't accelerate past 10mph, and if I press the throttle to accelerate it bucks like crazy. If I try revving the throttle by hand it bogs down real bad at about 1/4-1/2 throttle, and after pulling the plugs I've found that it's running very rich. Vacuum readings are still at around 10in, but no issue at all with starting up and it idles just fine.  Tried the hand over the AFM trick, it killed the motor instantly so I don't believe there's a large vac leak anywhere. Any ideas on the current issue?

[smoke]

You may already know this, but taking the vac advance line off is only to time it really, like in your driveway. It won't go too well when the timing is that retarded.

[smoke]

You can of course take or leave this advice, but I can tell you what I would try as a "just to see" method. I would not use a timing light and I would advance the timing while it was sitting there idling, just by ear to see what happened. I have a strong suspicion your timing is very retarded.

[NC280z]

I've got it set at the factory 7'btdc, and reconnected the vacuum line immediately afterwards, before attempting to drive it. Right now it's ran so rich that the oil smells very gassy, and the plugs will need to be cleaned. I've also noticed that the headers heat up very quick (MSA ceramic coat headers) don't know if this is normal. I'm going to double-check and make sure the thermotime/water temp sensor connections are correct, and investigate the timing further as well. Might try and post another video now that it's a good bit more quiet with the exhaust reconnected.

[smoke]

Hot header equals retarded timing.

[I'm BLUE]

Just offering my thoughts on some of the problem in addition to others replys.

I haven't read through all this thread or responses , so might be redundant on my comments.

For the rich condition , and 10mph max speed condition.

 

*CTS (coolant temperature sensor located in the thermostat housing)

*CTS Connector as these get corroded all to poop all to easy !

*Fuel pressure regulator (located on the fuel rail , and you can rent a tool at some auto-parts houses with a deposit down)

*O2 sensor (it's like an an off-switch since it's a narrow band). You can test with a multi-meter *carefully* , but they don't cost that much money.

*AFM rubber boots between the AFM and the throttle body are FAMOUS for tearing/ripping tiny tears or creating random vacuum leaks (easily cause grief) = shoe glue. You have to peel/fold it back to look for the tears I'm talking about (have it off the car sometimes.

*TPS - Check your throttle position sensor. They do need to be re-calibrated here or there or the switches cleaned at the least.

*AFM is out of spec. It could need to be redialed in. Sometimes they can't be repaired , but won't know until you look.

*Short or corrosion somewhere in your engine wiring harness back to the ECM. Yes they get corroded. I've split open a few to repair.

*Vacuum hoses ... every single 280z and 280zx I've ever owned has had some kind of leak or potential vacuum leak here or there. Go to NAPA they are best with the help.

*I've personally never seen a 280z or 280zx N/A ECM go bad. 280zxt ECM's are more likely to go bad by far over the last two. Owned quite a handful of these. I suppose they can go bad like anything , but it's towards-ish  the last thing to look at really.

*If you pull the oil filler cap or oil dipstick .... while the engine is running .... it should bog down/idle down or miss , and if it doesn't = you have a vacuum leak.

*Make absolute sure your muffler isn't clogged/blocked/partially blocked/fallen apart. People can put on whatever muffler new or used they wish to. I don't believe your year of s30/280z/1975 car has a catalytic converter from factory BUT if it does for some reason I would be very suspicious of it. Too much back pressure is a bitch. I've cut off quite a few clogged mufflers , and catalytic converters that made the rigs run mucho better. For being a hobby at least since I'm not a mechanic. It's bad enough that an engine can't breathe when running perferctly.

 

When I first got my 280zx L28et (relatively the same system as the L28e with a few different parts/injectors/AFM/computer) I jossled a vacuum hose accidently while looking things over to start it up (it wasn't running). It finished splitting , and the car would idle "ok" once started , but wouldn't go over 10mph like you're stating. I measured , and replaced EVERY single vacuum hose with replacement SAE hose from NAPA. Most of it fit good , and one size fit "fine" enough.

 

140psi on an engine that's not fully broken in... isn't really to shabby for the lower compression dished piston L28e engine.

My rebuilt L28e ran around 150-155psi on all 6-cylinders for years pretty well.

 

Wouldn't use the brake booster hose to check vacuum.

Use a nipple off the intake manifold itself there's usually a free one or one you can rob.

Clean your throttle body carefully as well , and check your

 

Here is the FSM I'm sure you've already found the link = http://www.xenons30.com/reference.html

[NC280z]

I appreciate the insight, in order to help others who might post assistance I'll put what all I've done below:

 

-new injectors, new injector connectors (old were corroded badly)

-new vacuum hoses for all vac-components

-new PCV valve/hose

-new coolant temp sens/switch/thermotime, with new connectors

-new AFM and TPS

-new distributor

 

As for the vacuum gauge connection, it's not hooked up in-line with the booster, it's just off of the port itself. I've tried other ports on the manifold and the readings were the same. Also, the engine I built uses the late-model l28e flat-top pistons, rather than the dished stockers. The head gasket is a Fel-Pro gasket, no clue offhand as to what the thickness is and how it would compare to the OEM gasket in relation to compression. 

 

Thanks again for the input, I do appreciate any help you guys offer!

[datzenmike]

20% leakdown is way past bad. Try again, but listen at the exhaust pipe and then the intake for air sounds on each cylinder. Are the valves properly set? Tight clearance will leak vacuum on the intakes. Worn valves also.

[NC280z]

The engine is well below 20%, I had mentioned that it was less than that because 20% is the benchmark for gauging if an engine needs a rebuild. The head has also had a 5 angle valve job conducted, and I've triple-checked the valve lash after running the engine (to include rocker arm wipe pattern) I'm betting on Smoke's theory of late ignition timing, although there may be more causing these issues.

 

How much (in theory) could a leak at the oil filler cap/dipstick/pan gasket affect vacuum, as Blue stated? I thought that the positive pressure of the crankcase didn't  affect intake vacuum. 

[smoke]

Should not be any change from that.

 

Sorry if you mentioned this earlier, but is it just a standard timing light you are using (no dial)?

[NC280z]

It's a standard timing light from Autozone. I didn't think the crankcase system would have an effect on the vacuum readings.

[smoke]

Yeah, I say advance it just to see, it won't hurt anything.

[datzenmike]

The intake vacuum shouldn't be affected by when the fire is lit. Both valves are closed and the intake doesn't open for another almost 360 degrees.

 

Valve timing can though. The intake opens about 50 degrees after BDC. Too retarded and the piston rises too far up the cylinder with the intake still open pushing some of the charge back into the port. Basically taking a bight and spitting some back out.

[smoke]

It will have 'some' affect. my thinking is that his cam may have some kinda heavy overlap, which can make a funky mixture at idle, if he lit that mixture a bit sooner, it would give it a better burn. What rpm is it idling at anyway?

[NC280z]

I've got it set to idle at around 750/800rpms. I've used a formula posted online to calculate overlap at 41' (intake+exhaust duration/4=x. x-LSA=y. yx2=overlap)

[smoke]

Not measured at .050 is it?

[I'm BLUE]

How much (in theory) could a leak at the oil filler cap/dipstick/pan gasket affect vacuum, as Blue stated? I thought that the positive pressure of the crankcase didn't  affect intake vacuum. 

 

Well what you just stated was exactly what I thought as well until I found reading about it then trying it on my cars. It was one of the ways to test for a vacuum leak on these engines quickly :)  . My 280zx's all would have a vacuum leak at idle when the oil fill cap was pulled if all was well , and depending if I fixed the vacuum leaks first before conducting the crude test .. lol. I would call it significant BUT I only primarily used to test for leaks in other parts/hoses/evap system/etc of the system were sealed up + ready to go at idle. Any leak on these systems is significant with our flappy door AFM's lol. Every now in a blue moon one of the dipsticks are bent just right or the caps crusty/dry enough on ocassion that they need to be replaced. Granted keepng in mind any oil filler cap can seal when tight enough lol.

 

It's something I didn't think about or realize on my own.

 

I appreciate the insight, in order to help others who might post assistance I'll put what all I've done below:

 

-new injectors, new injector connectors (old were corroded badly)

-new vacuum hoses for all vac-components

-new PCV valve/hose

-new coolant temp sens/switch/thermotime, with new connectors

-new AFM and TPS

-new distributor

 

As for the vacuum gauge connection, it's not hooked up in-line with the booster, it's just off of the port itself. I've tried other ports on the manifold and the readings were the same. Also, the engine I built uses the late-model l28e flat-top pistons, rather than the dished stockers. The head gasket is a Fel-Pro gasket, no clue offhand as to what the thickness is and how it would compare to the OEM gasket in relation to compression. 

 

Thanks again for the input, I do appreciate any help you guys offer!

 

Ahhh sounds like been pretty hard in your work and research to me !

Honestly those compression numbers arn't that great for a flat-top piston 280z/x engine granted it probably hasn't had the chance to break in yet :) as we know. Def don't give up on it. My 82' 280zx flat-top org engine internals w/128,000 when put in = 170-180psi across the board (years ago)

EDIT: Looking at what head you're using exactly as well. (will thumb through).

Fel-Pro is closer to the thinnest gasket we can use

 

One thing you might consider is that the keyways in the crank (front) get "wallowed out" or work looser over-time.a

Harmonic balancer's can seperate = cause false sense of timing as well (The MSA ones need to be machined a bit more before being installed).

If your oil pressure was down I "suppose" that could cause some issues with the timing tensioner/chain slack. (just a far reaching thought not likely , and I'm not really sure how much if at all since their is a spring in the tensioner that exists as well).

If your head was shaved a bit too-much ... and the cam towers not shimmed up in combination with some other issues could easily cause "some" problems but I truly don't know how much "exactly" in combinations with other exact systms involved on your exact s30 car.

Decked block on top of that as well although I've never done it to an L-series.

I didn't read yet if you have a stock cam or a re-grind as well. (I'll try to read later when time).

 

Remember you can advance your Cam dowel pin 2-more positions until maxed to help with timing chain wear/slack. (I'm pretty sure you know this though) :)

 

If for some reason or whatever reason you remove your cam-towers w/the cam in it down the line or solving your problem.

Mark them first with steel punches or numbered steel punches "very lightly".

Keep them in order obviously , and make sure you don't accidentally lose any of the dowel pin guides.

The cam-towers will line back up if every single one of them are presenet and accounted for = 12ft lbs at the very most. Torque in 3-4 stages , and spin the cam as you're torqueing.

 

I have a set of Federal Mogul Chrome rings I'm saving for an excellent bore (the least) or re-bore engine.

I've been hesistant to use them as I've had a couple of friends have a harder time getting them to seat properly.

 

Of course all of this is extra or directly related , and in addition to what others are replying with :).

Sorry if redundant again. I just got done eating and have a broken car I have to get back on.

Please note that I'm not a mechanic , technician , so take it all with some thought + a grain of salt lol.

[NC280z]

Also, I may have forgotten to mention that I installed the cam normally, that is, as though it were stock (without using a degree wheel). Delta Cams sent the regrind back to me without a cam card, and I didn't think to have the cam mic'd before installing it to double-check it. Should I go through the process of degreeing the cam?

 

I'm going to start today by checking the ignition timing, and ensuring that the coolant temp sens/switch and thermotime are all up to par. Once I've verified that I might get down to the nitty-gritty of removing the front cover, and making sure that the cam isn't retarded. I've had the dizzy rebuilt by MSA, do I need to make any adjustments to the phase difference after a rebuild?

[datzenmike]

You don't need to remove the timing cover to check the cam timing. Provision has been made for moving the timing advance or retard to correct for chain stretch.

 

Assuming that the timing may need adjusting it easier to loosen (but not remove!) the cam retaining bolt now. Then...

 

Set accurately to TDC by turning the engine clockwise and lining the timing mark on the pulley with the saw tooth timing scale. The engine must be brought up to TDC in a clockwise direction only! If you overshoot and back up you will introduce slack into the chain and the reading will be meaningless. If you ober shoot back up well before TDC and do again as many times as needed to get it right.

 

No look down at the back of the cam sprocket through the top hole. Some after market sprockets don't have the proper holes located so find some way to look down there with a flashlight.

 

The backside of the sprocket will have a V or U shaped notch.

Just above and behind it on the cam thrust plate will be a small horizontal etch mark.

If the cam is properly timed the V will be just below the etch mark or just slightly to the right.

The cam below is perfectly timed...

 

 

 

If the V is to the left, the sprocket can be removed and turned counter clockwise to the next cam dowel hole on the back. This will add about 4 degrees advance to the cam. If it is far to the right of the mark then the sprocket will need to be moved clockwise to the next dowel hole to retard it.

 

Under no conditions remove the cam sprocket without blocking the chain tensioner. If you don't know about this find out

[NC280z]

Just got done for today. Started the engine, verified that the ignition timing was at 7'BTDC, bumped it up to about 12-13'BTDC and saw a slight increase in intake vacuum. Engine is still running rich, and I tried removing the oil-filler cap while running (as was previously suggested), doing so immediately bogged the engine down tremendously.

 

Removed the front cover to verify timing marks for the cam, I've got 42 link-pins from the  #1 cam dowel mark to the crankshaft gear mark. Using the #1 cam gear position, the cam gear V-notch is just right of the cam tower notch at TDC. Anyone have ideas on what to do next? I've been told that the cam gear notch should be just right of the tower notch, so if that's true the cam is timed correctly. Should I advance the cam further? I'm half-tempted to find a stock camshaft and ditch the dual-pattern cam I have now, since some people have said that Delta doesn't always grind cams the best.

[ggzilla]

Summary:

 

* advancing timing did not restore the lost vacuum

* removing oil-filler cap has a large effect on running, which suggests it is sealing well

* you haven't tried the alternative cam timings yet

 

Good work so far. Don't stop now.