|
An enigma insues...
If y'all haven't gathered by now, after a long difficult surgery, the patient is having trouble in the recovery room!
It fires, but is missing badly at idle, and no change in the missing under some throttle up to 2500 rpm, except some of the missing clears up momentarily. On fire up, there is sometimes some sharp "barking" thru the exhaust - which lead me to thinking ignition. The coils were new two years ago, and FWIW they ohm out between 5.8 to 6.2 across the posts. The plugs were new at the time the coils were installed; platinum with 3k miles - they look "perfect". And, inspecting the plugs after a short run, I find a couple plugs that are wet with fuel, yet the plug on the opposite side of the coil are firing. And, some plugs appear dry, but fouled and a bit cooler to the touch - so I'm guessing they have been firing at least some of the time... My pressure washer and a Honda I owned both suffered gummed ports in the carbs after storage over the winter, so my injectors came into question (reason for the earlier Accel parts# request.) However, I got to remembering that since I run with secondary throttle plates and actuators removed, my secondary injectors come on just off idle (via the Marc Haibeck chip design), but there's no appreciable difference in the missing characteristics when throttle is added: point being it would be highly unlikely both injectors on the cylinders not firing would be equally plugged. Injectors??? The injectors had been replaced at the time I bought the car - friend showed me the receipt for $1200+ at time of purchase. Just to check it, I ohmed them all and they checked out. So, I rigged up a pair of wires from the battery to alligator clips, clipping one clip onto one of the posts on each individual injector in turn, and with the fuel rail pressurized, I momentarily bumped the other alligator clip against the remaining injector post while looking down the IH runner to observe the individual spray pattern. All 16 injectors made a crisp "click-click" sound i.e., they didn't sound gummed up - is my point. And, the spray pattern characteristics appeared identical to the eye: marginalizing injectors as the issue, for now anyway. The one item I changed in the interim before first turning the switch was the knock sensor - as the plastic connector piece was damaged. There are no codes, but the scanner did show only 17* advance at 1500 rpm...THAT seems a tad low, and come to think of it, the engine runs like the timing was waaay retarded (e.g., the "barking" and the sluggishness of throttle response, etc observed over the years fussing with SBCs.) Oh, the O2s readings are a bit wacky, but they haven't had much time to heat up (burn off un-burnt fuel). Besides, it was running in open loop still and so the O2s wouldn't be having an effect in open loop anyway. The left and right integrators are both at 128. So! Some of the plugs are fouled up now, so I'm going to replace them with some fresh ones this morning...AND reinstall the original knock sensor and see what happens to my spark advance...I'm running out of options pretty fast. Have I missed anything? Stay tuned... P. PS: At times like this I am soooo thankful I cut off the coolant ports to the plenum. If I had to drain the coolant and then try to get the air pockets out each time...I'd be a little nutz by now! Now it is about a 20 minute job - if that -to pull it. :thumbsup: |
Re: An enigma insues...
Just a thought, but you said it's unlikely the injectors would both be plugged in a cylinder. I'm not sure that matters, does it? If you supplied 1/2 the fuel needed by the air in the chamber (because one injector was clogged), would it burn? I was of the understanding that past a certain mixture, the fuel would not actually ignite as it's too dispersed (something like 15-16:1)?
But it sounds like you've ruled them out, because you've visually seen them spray properly. Does your scanner show knock events, since you suspect the knock sensor? |
Re: An enigma insues...
Quote:
Yes - I should have elaborated on that - by "no codes" I should have said the knock count was zero as was the knock retard. Hmmmm... Now Bob G had an issue with a replacement knock sensor, the reason I was specific about getting one for a 90, as in 91 the sensor is different. However, the GM guy said the part number I gave him was the old Delco part number and he cross-referenced it to the new AC Delco number. But, in spite of all appearances and scanner readings, I'm dubious as far as the sensor goes. Ain't gonna cost nuttin to put the old one back in and see what happens, is my thinking now. Like I said: Running out of options. P. |
Re: An enigma insues...
Where did you get the Knock Sensor
|
Re: An enigma insues...
Quote:
Glad you chimed in... I got it from the local Chevy dealer. I kept the box and paperwork, "just in case" something weird (like this) happened. P. |
Re: An enigma insues...
Paul ohm both the KS (knock sensor)
If plastic was broken is the reason for replacing KS i would think still good. Also not too tight. Good luck Pete |
Re: An enigma insues...
Quote:
Together we've scoured the wiring issue, but nothing seems out of place - including the grounds. I'm going to check the low voltage connections on the coil packs again tonight, record a time-lapse record scan and graph it on the computer, monitor fuel pressure, and see what clues that brings. Oh, but I have this feeling something is being overlooked and how stupid I'm gonna feel when the culprit is finally found. But, at least the symptoms will be well documented - and posted here soze somebody else might benefit from "all this fun".:o OH! The damn thing has 3/4 of a tank of gas in it...A bit much to siphon, but I'm going to give that a try too, if all else fails. Then onto swapping ECMs? Just a thought. P. |
Re: An enigma insues...
With no knock counts and no knock retard, why would you suspect knock sensor? I'd ask Marc what timing curve looks like at that RPM/MAP? BTW, what
MAP/TPS readings are you getting on the scanner? |
Re: An enigma insues...
Paul is it possible that you got your plug wires crossed. I know you know what your doing but sometimes the simplest things can bite us in the azz. Just a thought my friend.
|
Re: An enigma insues...
Quote:
|
Re: An enigma insues...
Cam Timing?
|
Re: An enigma insues...
Quote:
Since we know who did it, an impossibility! |
Re: An enigma insues...
Quote:
|
Re: An enigma insues...
We will fix her or my name isn't Pete:)
Pete |
Re: An enigma insues...
Quote:
It "could be this and it could be that"...I'd rather not speculate until we have the issue "to ground". Once she' running again, at that time we'll write it up: what happened, how to check for it, how to fix it - before going back in the car!:rolleyes: Let's just say it isn't wiring - at least not at the moment. (But! I can now pull my intake plenum in under 15 minutes - and I have the coil-pack wiring memorized!) Hotrodding SBCs was all I knew before the ZR-1. The unfamiliarity with the LT5 engine, coupled with the computer aspect of it - was (for me) intimidating, initially. It still has its mysteries, and I'll be on the learning curve for some time yet. But, as anyone that has followed his wrenches (no, I didn't say "wenches"...Pete) knows, the "shadows" give way to the comfort of familiar territory. At 7:45AM yesterday morning I took a wrench to my 100% assembled Z. By myself, working off of jack stands (no lift) and cardboard, and all the tools I collected on the first go-round, I had the engine out just after 5PM. The exhaust is up against the wall, trans on a floor jack under the car, clutch over here, plenum over there...looks like a disaster again. Hopefully, once back together, it will be the last time for a while. But, if I have to pull the motor again for some reason, other than the time to do it, it falls into the "no big deal" category; and that's a good thing. I feel like I'm learning about this one of a kind Corvette, and in spite of the setbacks, each has been a learning experience, and it would be a lie to say I wasn't enjoying the learning part at least. However, I wanna drive it so bad I can taste it! So there's that aspect burning in me as well! Stay "tuned"... P. |
Re: An enigma insues...
J. C. on crutches! I'm hopeful that it is something minor Paul. I can't read this thread and not think...." jez if it can happen to the FBI brain trust...what would I do by myself!??!"
Man I do feel for you....wish I knew the answer as I'd fork it over in a skinny minute. I hope this is not as serious as I think it sounds.:pray That has got to be some kind of record for pulling an LT5 solo, no?:worship: Here's to this bad dream coming to a speedy conclusion! :cheers: Tom |
Re: An enigma insues...
With freinds like Pete not far away you'll have it fixed soon. Even if you have to pull the engine again. Hahaha! That would be F'ed up dude. I sorry! I know it's not funny. I'd have to do the same thing and I don't have a guy like Pete to guide me through it like Yoda.
http://i301.photobucket.com/albums/n...0/Yoda-ep2.jpg Id have to figure it out as I went along. And Call Corey for help when I needed it. |
Re: An enigma insues...
Paul, think of it this way - with all the experience, you could probably become a new mechanic for Marc:mrgreen:....more power to ya buddy!!:worship:
get 'er running..:thumbsup: |
Re: An enigma insues...
The down side to that is Mechanics don't make squat unless your a Ferrari/Porsche mechanic. Unless you think $20 an hour is good money.
|
Re: An enigma insues...
Quote:
Last winter (while you were still on on Pete's garage probation;)) therein was a discussion about the KS. At one time, Bob G bought a new knock sensor, suppose to be for a '90. However, when firing it up, the engine would hardly run. The ECM was taking out (I think he said) 20* of advance, and it turned out that the knock sensor for the 90 is different from those of later MY LT5s. The key distinction was the ohms to ground: The 90 knock sensor is approx 98-101kΩ, whereas the KS resistance used on the newer cars is considerably lower (Pete and I measured 3.8kΩ on one such KS). When I bought my new one, I gave the GM dealer the AC Delco part number that Jerry posted. However, when the parts guy says, "Oh, this is the old AC Delco number. I'll cross-reference it to the "new" number", I became dubious... So, when my LT5 was running like a box of rocks, and there was no apparent reason for the change, I remembered that conversation about the KS. However, in spite of no knock counts or retard values, I put the old KS back in. But, it made zero difference in the way it ran, and the knock counts and retard values were still zero. Shoulda 'splained my reasoning better, Dom. Sorry for the cornfuzion! P. |
Re: An enigma insues...
Quote:
P. |
Re: An enigma insues...
Quote:
Right. The ECM wasn't commanding any Spark Retard so "not likely" it was the issue. |
Re: An enigma insues...
Paul, now that it's running again, can you share what was the problem? Would help the rest of us sleep easier if we know what to double, triple, check.
Todd |
Re: An enigma insues...
I think there was an old pull tab off of a Falstaff Beer lodged in the valve seat.:fahne:
|
Re: An enigma insues...
I'll let Pete fill in the technical dimensions, were it not for his expertise I would have been in a "world of hurt". But, in a nut shell the machine shop entrusted to do the valve job, omitted checking the resulting valve height. Apparently, they don't do many/any DOHC engines - mostly LSx motors.
The unloaded lash (my word) within the LT5 lifter is about 120 thousandths. Preloading takes up about 75, leaving about 45 for expansion...and most first-time valve jobs are accommodated OK. However, we've reason to believe this wasn't the first time the valves had been worked on - after the fact - and all of the lash was gone on several valves. The result was that those valves never fully seated/sealed: NO COMPRESSION! Furthermore, apparently there were several seats that were less than perfectly perpendicular to the valve - to the point lapping would not rectify it: they had to be re-touched. Once all that was done, Pete did a leak-down test to determine sealing integrity, and I did a baseline compression check of my own before bolting it all back together. Perhaps Pete will answer specific questions regarding measurements and tolerances, but I'll say this: It doesn't matter how good this or that machine shop is, one would be well advised to fully understand the process being done to the point of knowing what to ask for and what to expect from any process, regardless. To that end, I think it is high time some sort of book be compiled with exactly this and so many more examples of what to do, questions to ask, and measurement procedures, be compiled. Hmmmm...I promise more on that later! P. |
Re: An enigma insues...
Lifters have .120 fully loaded anything above that the lifter is totally plunged and will hang valves open,cams take up .075 from base circle.
It's .075 above the main journals so when you bolt down the cam it will push the lifter down .075 plus the factory has the lifter above the journal another .015 so a stock motor takes up .090 of the .120 you have .030 left in the lifter. If you do one valve job should be ok if you do a second or third valve or even a crappy valve job the valve will sink into the hole which will bring the valve higher into the lifter bore,which means you will have to cut the tops of the valves to bring them withen tolerance. So if the valve sinks in/comes higher into the lifter bore .035 your valves will hang open and will have very low compression #'s. A leak down test will tell you if it's exhaust valves or intake valves. If hieght checks good then i would say it's a bad valve job. All of the above is an easy fix by just cutting the tops of the valves besides doing the job all over again. Also be carefull when taking/cutting the tops of the valves you now have to make sure you don't take off too much you still need the valve stem to be above the retainer at least .020-.025 otherwise the lifter will knock the keepers out then you will have bigger iisues. Most have worked on SBC,the LT5 is a finicky/different beast,not that it's hard just different. LT5 is like a woman you have to work on them for a while till you find her sweet spot after that she will take good care of you and keep you very happy for a very long time. LOL Hope i explained it all ok,if not ask away. Pete |
Re: An enigma insues...
Quote:
Pete |
Re: An enigma insues...
Pete, Its all Greek to me;)
|
Re: An enigma insues...
Thats a Pete joke, he is Greek.....ok pretty lame, but had to do it
|
Re: An enigma insues...
Quote:
I guess gone are the days when you could just check the installed height of the spring assembled on to the valve stem with the valve in it's port/seat?:cry: |
Re: An enigma insues...
Quote:
Yes,and that is on the lowest point/base circle of the cam lobe. Lee it was all Greek to me but thank god i'm Greek and i understood it :-) This is why we need a tech session with a motor/heads all apart it's easier to understand it when you see it. Pete . . . . . . . . . . |
Re: An enigma insues...
|
Re: An enigma insues...
Pete proposed a public autopsy of my 90 motor at his place, if there is interest and I can get someone to haul the body over, I would be fine with a tear down at petes.
|
Re: An enigma insues...
When Pete told me about this, I pulled out the GVD heads I have to check. Basically the top of the 2 lifters on either side of the cam bearing surface and the bearing surface should be nearly one continuous plane. Should be able to slide fingernail from
lifter to bearing and then back onto next lifter with hardly a hangup. |
Re: An enigma insues...
If you recall I picked up a motor cheap from 8upZR1 who pulled the LT-5 after the car would not run properly. I am guessing the afore mentioned issue was his problem.....along with cutting the intake gasket surface too thin.
We will know in the next month or so if this was the issue. |
Re: An enigma insues...
Couple of things that need mentioning here. 1. You can use 90-92 lifters in all years without modifications HOWEVER you cannot use 93-95 lifters in 90-92 without cutting the valve stem slightly. The later lifters are taller than the earlier lifters. So if you do a valve job on an early engine and replace the lifters with the later design you have just created a nightmare for yourself. 2. When you do the leakdown test time will effect the compression and leakdown. JL long ago told me a leakdown test on a LT-5 is a crapshoot because you can get one set of figures with an engine with lifters that have bled down and another set for one with pumped up lifters so they never depended on leakdown info on LT-5s.
Tyler |
Re: An enigma insues...
Tyler, i don't think there is a differance in the lifters.
There is a differance in valve lengths. http://www.zr1netregistry.com/ZR1_specs.htm#9 Yes,your are right about leak down this is why i say she is a finicky girl there is alot of things one needs to know/check. Once you crank her a bunch or run her for a few minutes lifters will bleed down. What stinks is if one screws up it can cost some real $$$$ which will make taking it to a tuner in the first place a bargain. Pete Quote:
|
Re: An enigma insues...
Hey PETE
Did ya ever know about that Gyro Stand on Ashland? Have you ever been by it? I did a "Pete the Greek" google and found it -- right here in Chicago of all things. Guess it just proves that Chi-Town has at least one of everything. You should get a photo of you and da Z in front of it someday. That would be KOOL. ======================= A giant picture of pressed lamb on Pete the Greek's sign lets you know where the joint's specialty lies. The gyros here win the award for succulence, teeming with onions, tomatoes and cucumber sauce, the meat cooked to perfection. Pete also makes a mean cheeseburger, complete with home-cut fries. The hot dogs do a Chicagoan proud, with a perfectly steamed bun, all the trimmings and no ketchup to be found near the dog. Breakfast at this Greek-owned spot (like you didn't know that) includes the staples: sausage, eggs, breakfast sandwiches and omelets served fast with loads of hot coffee. None of these options exceed $10. This newer brick-and-glass storefront, located next to a gas station, provides ample seating for folks who want to have a seat and savor their breakfast or lunch, with counter seating surrounding the main dining room?perfect for gazing out onto the street while eating. =================== This place has the best gyro. We learned about it from working nearby and we come whenever we get the gyros craving. I don't care much for fast food or gyros, but this place makes it worth it. The owners have friendly service and are attentive to customers' needs. =================== 312-243-6199 >> I called there and they still go by the same name. However Pete sold to the present owner many years ago so no Pete anymore. =================== BTW Paul congrats on getting the Z going again -- sorry about all the "Pete stuff" not trying to hijack your thread here. LOL -- Glad to see the symphony of the LT-5 is rumbling once again south of the I-80 line.:cheers: |
Re: An enigma insues...
Quote:
P. |
Re: An enigma insues...
Quote:
Tyler |
| All times are GMT -4. The time now is 06:19 AM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2025, vBulletin Solutions Inc.
Copyright ZR-1 Net Registry 2025