ThorOtheBIG

Hey all,

First I am working on my friends '92 RS 3.1L I myself have a '94 Z28 LT1. I did a compression test on all cylinders and they were all 100-120. That seems fairly low but not too bad for these motors. What is the typical compression numbers?

Also, I'm no expert, but I would wager that the following pictures show a totally wasted distributor..

Six_Shooter

iTrader: (2)

Compression test seems to be ok, as long as they are all about the same.

The dizzy doesn't look too bad, are you having problems with spark?

Maverick H1L

iTrader: (8)

That dizzy looks better than my original (or the one that is original to my engine, can't say for certain which parts were swapped or not as I didn't change out the 2.8), which still works (or would if it was in one piece and I still had a factory setup).

As for the compression test, I'd check the valve lash. Only time I had a compression test on my 3.1 test in the 130s PSI range was when the head gasket had gone bad between cylinders 3 and 5. Otherwise, it tested on all six (except cylinder 6 which was high due to oil control problems) in the 160 PSI range (stock 3.1, not now). Even my dying 2.8, with a bad rod bearing, tested in the 140s. Generally, low compression in all six is an indicator that the valves are too tight, for one, or other internal problems... Has the engine been worked on recently (head gaskets, valve stem seals/guides, etc)?

ThorOtheBIG

The vehicle has been sitting for a year or two. We replaced the plugs (each had tons of crap on the ends). We tired starting fluid and it would pop pop for the first crank then just crank. The distributor cover only had one bolt holding it on. Although when I unplugged the #4 wire and held it I did get a shock every once in a while. Not quickly enough, personally. When I did the compression test I swear that the injectors were working, at least some of them lol. Also, the plug wires were all over the place, not in the right order at all. The owner of the car is paying my friend to fix it up (he is a body and paint guy) and I'm mainly just working on the engine side of things for fun.

So it cranks, barely a fire. I'm thinking replace the distributor, especially after seeing how it looks (btw, two of those metal arms are hitting eachother when the dist spins). Anyone know the ohm specs for the wires? And I swear for the life of me I cant find a schrader valve or anything on this fuel system to test it.

As a side note I did check the three main relays on the upper righthand side of the engine bay, all test fine. I don't think VATS is an issue b/c the vehicle does crank.

Thanks for the replies guys!

EDIT

Maverick H1L

iTrader: (8)

The low compression isn't helping to start the engine, for starters... Do double check your readings as I know I've occasionally had issues getting the pressure test port into the spark plug hole tight enough. If there was assorted crap on the plugs, the valves may be getting held slightly open.

None of the plug wires should have more than 20K ohms resistance, or 10K per foot (general rule for plug wires!).

Fuel pressure test port is in the back of the plenum under where the brake booster vacuum hose connects.

If he's got the money, then do replace the dizzy... The replacements are put together with better pickup coil assemblies. If not, look into replacing the pole piece and possibly the ignition module and/or the pickup coil.

ThorOtheBIG

Yeah he has money for it. We will be replacing it.

Cylinders 3-6 where all 120. 1-2 where like 105-110. I thought about retesting those b/c I wasn't too sure if I had it screwed into the plug hole tightly. Both 1 and 2 gave me some problems.

I'll check the resistance on the wires next time I'm over there.

Seems like a very convenient place for the fuel test port lol.

Well I sincerely hope that we can get it running without having to do any headwork. I don't think my friend wants to take it that far.

Anyone think bad fuel? My friend does but I would've figured that we could've gotten it started with starting fluid if fuel was the issue.

Maverick H1L

iTrader: (8)

Double check the compression in all 6 first before you dive into the fuel system... Next thing would be to take the valve covers off and check the valve settings if the compression is indeed THAT low. Good news there is that you can make sure the fuel injectors' resistance is within specs (11.8 ohms minimum per injector) and refresh the top end gaskets.

Yes, the fuel pressure test port is a pain on these cars.

Six_Shooter

iTrader: (2)

Since the engine has been sitting, and not fired for an extended period of time, first thing to do is a complete tune up, including cap, rotor, plug wires, fuel filter, would also be a good idea to drain old fuel and replace with fresh, air filter, oil and filter.

Since you say you are getting spark, that would indicate to me that the dizzy is not faulty, or at least not bad enough to worry about right now.

ThorOtheBIG

You two guys, thank you for your replies, quick too. I'm glad I have a two dudes who have posted once or twice before lol.

Not to be rude. But could yall possibly re-read the #4 post again? It seems some of that info was crucial and might have been missed? I only say because your responses seem to have missed some minor (but major) details in post #4. But, I will continue on with replies to your new posts.

Maverick:
I will double the 1 and 2 next time I am there. Although I am sure of the others, especially since all read exactly 120. I am not diving into the fuel system until I can get the engine to fire when using starting fluid. Is the compression so low that it wont run? I don't think 120 is all that low. If it were in double digits then yes. BUT if we cannot get it to fire and our last resort is head work you are saying to adjust the valves first? Thank you for the ohm numbers for the wires and injectors. ....(Maverick, I just re-read your post about the head gaskets bad and you were at 130psi. I'm assuming it would still fire, yes?)

Six_shooter:
The entire distributor is being replaced. I am going to ohm the wires and see if they are in-spec. Air filter is good. It has a K&N! WHOO!! lol. I will do oil and oil filter once it gets running. Oil is at proper level and not too black lol
. I am thinking about the fuel but I am still concerned because starting fluid didn't help. I just don't feel like draining the tank, yet.

I think we need to get a new dizzy on there. Make sure the wires ohm in-spec. Make sure the ignition timing is correct. Then crank. If no start, use starting fluid. If starts, check fuel pressure, then ohm injectors, etc. If no start using starter fluid... Start looking at ecu, vats, crank/cam sensors?? Again, really trying everything before pulling valve covers. Dude doesn't want me to pull the top of the intake so I can get to the fuel, so I am trying EVERYTHING before needing major investigation.

Thank you guys!

Maverick H1L

iTrader: (8)

Ok, first, the firing order is 1-6, in that order, the #1 being the front PASSENGER'S side, not the driver's side (it's not based off of a V8 and it's not a Buick engine).

Second, you already said that the engine wasn't firing on starting fluid, and since you've already said that the compression is in the range for lawnmowers, I would tend to think you're losing compression through the valves. It only takes about half a turn too many on the rocker nuts to lose a LOT of compression. Keep in mind that my 3.1 had 4 other cylinders with proper compression while losing compression in 3 and 5 and you could tell it was weak (weaker than usual). It may run if/when you get the firing order and ignition timing straightened out, but it is going to run like garbage.

Third, tell the guy that any number of the intake gaskets may need to be replaced. If you're not sure the injectors are even working, you WILL need to pull the upper intake at the bare minimum to get at them. You can test the injector resistance without pulling the upper intake, but it's highly likely that if the injectors are factory, a couple are shorted out internally. To do this, locate the 6-pin connector by the air conditioning compressor and unplug it. Test the resistance between the pink and blue and green wires (power is pink or pink/black and the ECM ground is either green or blue depending on the bank). If the resistance is any higher than 4 ohms per bank, you have a shorted injector. (will come out at 6 ohms or higher depending on how many are bad). Also, the valve cover gaskets may have dried out by now and are leaking oil and engine vacuum (thanks to the PCV system). :edit: Also, while you have the injector harness disconnected from the main harness, connect a test light between battery POSITIVE and both the blue and green wires while the engine is being cranked. The test light SHOULD flash as the ECM provides switched ground to try to fire the injectors.

There are no crank and cam sensors. The only sensor of that type is the pickup coil in the dizzy. The ECM reads off of the ignition module to find out if the engine is cranking or not.

ThorOtheBIG

Lol, yes I know which cylinder is which. Yeah I told him the only way to get into the fuel system would be removing that intake top. I will do the tests on that terminal for injector resistance, thank you.

Oh.. yeah, and one other thing I just remembered. When I FIRST cranked the car the vacuum line from the brake booster flew off. It didn't do it again that day. The next day I went to crank it (for the first time that day) it did the same thing. But I can put it back on and crank again, it wont blow off. I haven't seen anything like that before.

Maverick H1L

iTrader: (8)

Is it firing through the intake, if you can tell? Sounds like the hose is somewhat loose and the backfiring (if present) is blowing it off due to increased manifold pressure with the throttle closed...

project89

iTrader: (1)

those compression numbers are fine, when u did the compression test did u have all 6 spark plugs out and have the throttle held wide open??? if not that will affect the readings

btw my brand new 3.1 motor that i assembled myself only had 125 psi cranking presure

make sure the balncer on the front of the motor didnt spin the outer hub this will throw the timming marks way off and the motor will run like crap/ or not at all if this has happened and ur trying to set intial spark timing off of it.

rotate the motor so its at tdc on the compression stroke on #1 and verify the timing marks line up if they do then drop the dizzy back in
and proced to set the timming to 10* btdc with the est wire unpluged

if the plugs happen to be fuel or oil fouled no amount of tinkering will get it to fire and plugs are so cheap i would start with a set of new plugs

acdelco r43tsk's r what u need for the motor

ThorOtheBIG

Maverick:
Is it firing thru the intake.... like a backfire? No. Not enough combustion has taken place to determine that. ANY firing was just a couple of little pop pops but then silence (minus the car cranking). I don't think any backfire has taken place, otherwise I would've stated it so. As far as that brake booster hose who knows.. It only happens the FIRST time you crank it on any given day. Notice: I've only worked on it two days lol.

project:
Not all six plugs were out. By the end of the tests they were. I have never done a compression test with the throttle open. Not only in this forum but also another I just recently found out you 'should' have the throttle at WOT when doing the test. I have NEVER done a comp test with it open (were talking dozens) so I am curious as to if it is needed. What is the logic of having it open (I have a few thoughts but I can come up with reasons why it wouldn't matter except to show 'healthier' numbers)? God, I hope that balancer question was just one of those "i've seen it before" and not so much "it often happens." The plugs were replaced and they are Acdelcos. As far as timing goes we are waiting for the dizzy to show up.

So I suppose we are all done until I get that new dizzy on there and do the ignition timing huh? Which that wont be for at least a week or two but I am taking notes of all the "small" things to check and look for.

project89

iTrader: (1)

u need to do the test with all 6 plugs out, or as u progress threw the test the starter will turn the motor over faster as u go skewing ur readings

its the best way to get acurate readings

and the throttle should be wide open as when ur spinning the motor over it can create vacum in the intake which will produce lower numbers.

doing those just elimiates the variables that u can have with the test do they have to be done that way no, but it is the best way to get the best results cause after all u are lookng for numbers across all cyls that are within a certian percentage of each other +/- 10%

as far as the balancer its a common thing to happen on oem balancers that have some age to them the rubber in between the center hub and out ring starts to dry out after time and shrinks or starts to push out allowing the outer hub to move from were it should be in relation to the center hub which then throws the timing marks way out of wack

edit


also do not do another compression test till u have a dizzy back in the motor, the dizzy also drives the oil pump drive shaft and it is possible to beat up the bearings in the motor just by cranking the motor over with the starter if u have no oil presure

ThorOtheBIG

Okay he is supposed to have the distributor tmo.
How can I check if that balancer is bad?

Plan for tmo is to install dizzy set timing to what is THOUGHT to be correct and see if can get some fire. If not, I'll set to TDC with the balancer and time off of that. Worst case pull #1 plug and get to TDC then set ign timing off of that. Each time, if not starting on its own we will try starter fluid.

Anything else I should try? Sounds like a busy day if we dont get lucky

project89

iTrader: (1)

dont even mess with it just pull the number1 plug and and the valve cover so u can be sure its comming up on compression stroke and set it to tdc that way.

then line up the dizzy with the #1 plug terminal when u install it

this will also let u check the timing mark on the balancer at the same time , just see if the timing mark on the balancer lines up with the timing tab

ThorOtheBIG

OKAY so.... (NOTE THIS IS ALL WITH STARTING FLUID)

They had a new dizzy waiting for me BUT no new cap or rotor. Remember the cap was missing one out of TWO mounting screws.. SO.. Long story short, I installed the new dizzy and set timing to what was THOUGHT to be correct. We got a couple POPS but that was it (much louder pops now with the new dizzy). I pulled #1 plug and set it to TDC. Timing mark on pulley was in it 'correct' spot. The rotor was pointing to the front left of the motor (front left from motor's perspective). I read in a post that that is normally where it points. I realized later that I think the rotor was off by about 45 degrees because it was in-between posts and not touching one. Tried to crank it and we got no pops at all. The sun was down by then so I'll pull the dizzy and set the rotor so it is pointing at the post next time. He will also have a new cap, rotor, and plug wires for me. I will also have a fuel pressure test gauge.

SO... Thats where we are. Next time I will re-adjust the dizzy so the rotor points to the #1 post (set TDC again if nesc, but I think I just need to 'advance' it 45 degrees). We will have a dizzy cap that doesn't wobble around, new wires.
QUESTION: Say the wires and rotor/cap are all set perfectly, what does rotating the dizzy do? Advance/retard ign timing?

P.S. since we ONLY get any sort of POP with starting fluid that would clearly mean the fuel system has some issues too huh?

project89

iTrader: (1)

just be sure that when u set it to number 1 that is is on the compression stroke, if its on the ex stroke it will pop but never run

turning the distributor is what sets the timming, u can always rotate the dizzy till the #1 terminal is inline with the rotor instead of pulling the dizzy out and reseting it back in

ThorOtheBIG

Oh okay. I figured I could rotate it to a cap point, I'll look into that. Yeah i really couldnt tell if it was on the exhaust or compression stroke. I figured it was comp because the balancer had a 'slit' cut into it pointing towards where the timing marks would be. Well, I wont be able to get over there till this coming saturday, so we'll see then.

project89

iTrader: (1)

u have a 50/50 shot of getting it on the compression stroke, the mark on the balncer will be in the right place wether the motor is tdc on the compression stroke or tdc on the ex stroke

stick ur finger over the spark plug hole while rotating the motor over with a wrench or racthet and as its comming up on the compression stroke u will feel the presure building up under ur finger . once u feel that just slowly turn the motor over with the wrench/ratchet till the timming mark lines back up on the balancer

ThorOtheBIG

Okay, so I''m fairly sure its timed right now. I went over there and they had a new rotor and cap for me. Long story short, we got a lot more pops this time. I had misplaced my volt meter but that day I bought a real nice one from autozone. I checked the ohms on the #1 wire. No good readings. Switched to continuity. Nada. I pulled the coil wire (because obviously it worked if we got ANY spark) and ran the same test. Readings didn't cause the audible to go off but it did give me a reading. Waiting for new wires.......

ThorOtheBIG

Thought I would update:

Still waiting.

My response:

WTF IS GOING ON AT THE PARTS DEPOT?!?!?!?!?!?!!?!?!?!

ThorOtheBIG

Okay so he got new PLUG wires but they didnt come with a coil wire. Wtf.. More waiting. Good news is I move in there this weekend so I'll be with the car a lot more.