TOP END REFINISHING
 

2nd ed.:

DEFINITELY read Cliff's - user <Dynomite> - links when he links them. They're not always directly to the pertinent information about what you're on at some point in repair - you'll have to read it ALL to get to the info, but it's ALL there, and you HAVE to go through it. (Thanks a ton for that stuff Cliff). Use your bookmarks tool in your browser for the info when you hit it, and note that sometimes you'll run across info that's IMPORTANT at a LATER point...

edit:
This is continued from the DataMaster thread, for 'hesitation' diagnosis
http://www.zr1.net/forum/showthread.php?t=21259

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Next in the 'Hesitation' troubleshoot is spark plugs and wires check. Meaning access to the distributor to yank the wires.

This is about to become a Plenum Pull.


ed.:
This is now a plenum pull thread.
Link to the best procedure / tips / tricks?

Re: Throttle hesitation diagnostics?
 

I guess if you are going under there it might be wise to check all vac lines, check valves and mechanical/electrical connections too.

Re: Throttle hesitation diagnostics?
 

There is no distributor. You mean the DIS and ignition coil housing.
The biggest PITA for me are the 2 Ignition Module connectors up under the plenum. Other than that it's about a 15-20 min job IF you don't need to drain the coolant.

That TB looks like it hasn't been off for some time. Any obvious signs of torn gasket or vacuum leaks.

Re: Throttle hesitation diagnostics?
 

11 bolts out - she's loose. Something holding it from underneath?

and all the surrounding plumbing unhooked and tagged...

???

Re: Throttle hesitation diagnostics?
 

Great Photos....thanks....:handshak:

Re: Throttle hesitation diagnostics?
 

Not sure what you are asking :confused:

See Removing Plenum (including the 10 minute Plenum Removal)

15. Disconnect two small electrical connectors rear under Plenum (MAP and DIS).
16. Unscrew 1/4 bolt in Main DIS Connector rear of Plenum.

Re: Throttle hesitation diagnostics?
 

That the cam sensor plug. Feel underneath, should be a tang to unlock it. Be careful tho not to break the tang. Pull down and push back plug at the same time. You also unbolted the DIS connector right?

Re: Throttle hesitation diagnostics?
 

Drum roll...

:mrgreen:

Re: Throttle hesitation diagnostics?
 

... and now this message from our sponsor.

Re: Throttle hesitation diagnostics?
 

This is regular heat sink paste? For mounting CPU heatsinks???

http://www.zr1.net/forum/attachment....1&d=1381639984

Re: Throttle hesitation diagnostics?
 

Yep, heat sink grease. Get it at RadioShack. Is that coolant I see on #1 cylinder?

Re: Throttle hesitation diagnostics?
 

Do NOT drop anything in those open Injector Housing Ports. First thing is to tape those ports as quickly as you can.

You are doing extremely good in taking photos....appreciate that :handshak:

Re: Throttle hesitation diagnostics?
 

I missed this here Dominic - it lopes only as it I hit 1.6% throttle. No stumble at all, even on tip-in. I hit 1.6% TO, give it a TINY bit more gas - almost IMPERCEPTIBLE, and it starts to lope if I hold. Then it bounces from 1.6% - 2.4% TO, as shown on Datamaster. Once I get over 2.4%, it's perfect again through RPM range.

Re: Throttle hesitation diagnostics?
 

I noticed in the vid that the TPS% jumps around a bit. By "lope" do you mean a bit of a surge up and down the rpm?

Re: Throttle hesitation diagnostics?
 

I noticed in the vid that TPS voltage was about .61 volt when it hit 1.6% tps then the rpms began rolling between 900 and 1275 rpms at one point. The TPS changed from .61 to .63 volts.

Re: Throttle hesitation diagnostics?
 

Schrade, there is a note in the FSM about cleaning the TB. Page 6e3-c2-16. Good info to know with the throttle valve, IAC and TPS.

Re: Throttle hesitation diagnostics?
 

Uh-oh... I pulled the extension off of the TB first.

Didn't NOTICE any problem... :confused:

MEK for CLEANING? MEK is hardener for fiberglass resin. TPS wasn't immersed. IAC WAS liberally coated with WD and paint thinner mix (mostly kerosene in WD, and I pull excess off with a Shop-Vac).




Yep...


and thanks to Darryl for changin' thread name here.

Re: Throttle hesitation diagnostics?
 

Blow out the bolt holes with some lube til they run clean...

http://www.zr1.net/forum/attachment....1&d=1381700103

little spray on the bolts

http://www.zr1.net/forum/attachment....1&d=1381700442

Re: Throttle hesitation diagnostics?
 

I wouldn't try to take it out as I believe it is a tight press fit and you may not be able to re-seat it again. Its aluminum and is 23 years in there. Those hoses are crushed pretty good at the connections. I replaced mine with premium fuel line hose. Are you going to repaint anything while it's off?

From Marc Haibecks ZR-1 info (quote) "As far as I know GM has never documented any information about the use of Dag as a sealing and anti-friction method on the LT5 throttle body.
Dag is a general purpose material that is graphite based and is applied like paint. It's used in various industrial applications that need properties like a thick material buildup, low friction and high temperature range. DAG is a trademark of the Verick, Acheson Colloids company. It is easy to mistake the Dag for dirt. Dirt builds up on the Dag in the normal operation of the engine. These throttle bodies were cleaned so as to preserve the Dag. They were simply gently wiped with a soft dry cloth. The use of a solvent will remove the Dag.

The Dag was used to improve the seal of the secondary throttles. There are problems with the Dag coating. It wears off or chips off quite easily. It will come off if it is wiped hard. It will come off very easily if a solvent is used. It's easy for an uniformed maintenance person to remove it unintentionally. At a glance it looks like dirt.

Loss of the Dag coating can cause excess air leakage past the throttle plates and loss of idle speed control range for the engine control system.

I recommend that the LT5 throttle body bores should never be cleaned. In my experience a normally dirty throttle bore causes no problem. In fact a little oily grime around the throttle plates helps seal the throttles to minimize air leakage. It also lubricates the edges of the plates to avoid sticking. If the bore is extremely dirty or you just can't resist the urge to clean it, do it gently with a soft dry cloth.

I have tried to reseal throttle plates with little success. The problem has been with poor adhesion to the bore with the sealing material.

When the Dag is no longer effective I improve the fit of the throttle plates to the bores with a polishing process." (End quote)

Re: Throttle hesitation diagnostics?
 

Thanks again for the info there Franke...

Now's a good time to do another fuel pressure test, with some hardware out of the way here.

Where do I jump the pump circuit? How about the 2 second shut-off for this test?

And how to cap the line in front of the FPR???

Re: Throttle hesitation diagnostics?
 

IM is worth it's weight in gold. Think about where it has to survive and what function it performs. Like a number f other systems on the LT-5, the IM is a
Co-processor to the ECM performing functions the base code didn't do.

Re: Throttle hesitation diagnostics?
 

I would follow chart A7 in FSM to check fuel system on pages 6e3-A-29 thru 31. Your work looks good so far.

Re: Throttle hesitation diagnostics?
 

Didn't you convert this car to an automatic? It is a good possibility the calibration needs more "accelerator pump shot".

Re: Throttle hesitation diagnostics?
 

Didn't you first pull the clip holding the injector onto the rail?

Re: Throttle hesitation diagnostics?
 

Those seals always come off- forget about it if you can't see it anymore. Just find any Bosch style injector on a junkyard car and pocket a few extras.

Re: Throttle hesitation diagnostics?
 

I noticed the hesitation when I got it... Wouldn't vac supply to the FPR do that anyway? Or just not enough?

And I've always pulled the injector & rail assembly (and re-installed) as a whole - LT1's anyway. Is it easier to remove the rails withOUT them in place?

Re: Throttle hesitation diagnostics?
 

Should I pull the IH's next? Or DIS?

Re: Throttle hesitation diagnostics?
 

Injector looms - will they come up off of the back of the IH's? How?

Or does each wire have to come out of the loom first?

Re: Throttle hesitation diagnostics?
 

Do not remove those clips from the injector wire harness (just push on them and they will release)...if you remove them just something more that can fall where you do not want it.

Re: Throttle hesitation diagnostics?
 

yes

Re: Throttle hesitation diagnostics?
 

I would get a new PCV Connector from Jerry that fits tight and you do not have to concern yourself with it popping off again. That PCV connector you are cleaning has had its day :D

Oh....and when you get everything out of the valley......I started with a scraper........then degreaser....then HOT high pressure washer......then steel wool :D.....then more degreaser and then a final HOT high pressure washer.....and blow on that valley drain with compressed air after first squirting degreaser from the top down.

I put just a tad of anti-sieze on the plug threads and torque with 1/4 inch socket and spark plug adapter by feel (snug tight but not too tight) :D

Re: Throttle hesitation diagnostics?
 

Ignition coils I believe. Looks like they were replaced at some time. Measure them ohm wise. I agree with Dyno. I bought new rubber fitting from Jerry and it is nice and tight. Be sure to check the rubber pipe for cracks by flexing it. I had 5 holes in mine.

Re: Throttle hesitation diagnostics?
 

OK....have to ask.....who in their right mind would work on an LT5 during initial restoration wearing a nice White Sweat Shirt.....:sign10:

Re: Throttle hesitation diagnostics?
 

Dyno, notice the fingernails too--- no dirt. He must be a surgeon. White sweat shirt, no dirt.

Re: Throttle hesitation diagnostics?
 

Right mind? Me? :sign10: That's a good one! And you'll know who's NOT right mind when you see it dry-fit all together, and then UN-plugged AGAIN.

No dirt? That's FILTHY. Cliff's is clean http://i17.photobucket.com/albums/b7...lpacdetail.jpg

Clean as you go. Schrade's rule of :thumbsup: . Sterile Spic n Span clean. Probably get it all perfect, and never find out what made the 'Hesitation'. WAH. :-({|=

Makin' a list for Jerry's (and checkin' it twice)...

No di-electric grease on the Coil Pac prongs?

Photos
 

Keep up the great photo coverage.......

Where are your photos stored and you have thumbnail as well as larger photo (both....how does that work)?
My photos are stored on photobucket and I recently had to upgrade to Photobucket Pro because of a bandwidth issue. But then again I have over a thousand photos viewed on a couple Forums :D

I have three photos (total) of a Semi Truck and Grain Cart in a corn field stored on this web site (in my public profile) which someone complained that was poor use of bandwidth one time but you know how that goes. I used those photos to show that alternative of using this Forum as a photo host vice Photobucket and to also show photo sizing (those three photos I have stored here (Public Profile) are of three different sizes if you click on them).

That is ZR1Vette photo....here are my photos :)
I think I destroyed about three red sweat shirts along the way with oil stains I could not remove :D
I buy Simple Green in BULK (for clothes as well as hands).

1990 LT5
http://i287.photobucket.com/albums/l...b1ba5026d5.jpg

1991 LT5
http://i287.photobucket.com/albums/l...510aaf14f2.jpg

1990 L98
http://i287.photobucket.com/albums/l...631b879eb6.jpg

Re: Throttle hesitation diagnostics?
 

Nice engine bay pics dyno. Did you do all of the work?
Schrade, do you remember if your engine hesitation also occurs on open loop 1.6% - 2.4% TPS (cold engine) as well as closed loop (hot engine)?

Re: Throttle hesitation diagnostics?
 

Yep......and have the destroyed clothes to prove it now used as rags :D

Re: Throttle hesitation diagnostics?
 

The dielectric grease wont hurt anything and is not a bad idea. Any thoughts of spraying the plenum since you spent all that time cleaning it? I know your chasing another problem but you will hate yourself for not doing it while you are there. D

Re: Throttle hesitation diagnostics?
 

Schrade, do you know if those are the original injectors? Reason I ask is mine looked just like those before I replaced them with SS.