87_LG4

First things first. I have a rebuilt LG4 with the Q-jet and a rebuilt 700R4. Rear end is a 10-bolt with drums and 2.73. L69 intake and Hooker exhaust with no cat.

So I've been having some problems with my car lately. Mainly, it just about won't go up hills, or any sort of gradient for that matter. I thought it might have something to do with the very rich fuel mixture that was discovered during a dyno test. The test showed an AFR that started out at 10:1 at idle and climbed to 11:1 top RPM.

The main symptom is that if I try driving up a slight gradient at part throttle, the car will slow down. I guess I would also have to say that I cannot ever remember this happening in 1st or 2nd gear. So 3rd and OD, with and without lock up. If I try to give it more gas it will not go faster, it will only work harder and be much louder. Like a deep mechanical rumbling, is what I would describe it as. Often when it does this it won't downshift untill it reaches WOT, or close to it. Performance also suffers on flat roads and during WOT operations, but not as bad as up hill.

So I said I thought this had something to do with the AFR. I've tried to tune it on the car as best as I could, but to no avail. Also, I don't really have a way to measure the AFR myself. So I took off the carb to check it out, and I saw a wet fuel spot on the bottom gasket right underneath the main fuel jets, I guess it is called. I had previously tried to JB-weld them as they supposedly are prone to leaking. I saw that the JB-weld was discolored, and soft like rubber. It peeled right off. So I drilled, threaded and screwed shut the wells as per various tech articles. I also set the lean mixture screw using a 1.304" tube, as per shop manual, and the rich mixture screw so that the MCS has 4/32" of travel. The idle mixture screws were set to 4 turns out. TPS set to 0.48V, float set to 14/32". I had throttle shaft bushings inserted to remove play in the shaft and thus vacuum leaks. Also put a minor bend in the secondary lock out mechanism, so that the secondary throttle bades will stay completely shut. Before there was an ever so slight gap between the casting and flaps. The choke operates correctly. The TV-cable was set after reinstallment of carb. I also made sure the fuel return line was unclogged, as with the charcoal canister vapor line. I also installed a new O2 sensor as I think I fried the previous trying to use a voltmeter to check the AFR (signal wire melted on header). With the carb back on the car, I used the idle mixture screws to determine correct dwell (30* on six cylinder scale), which was at 4 3/4 turn out. This also gave me 20" hg. Idles around 700RPM. Timing set to 8* advanced, brand new MSD dist, wires and AC Delco plugs.

I had hoped this would do the trick, as I was about to set of on a 450 mile trip. This is where it gets annoying. I thought I had everyting correctly set, but now it _intermittently_ won't go up hills. Sometimes it will fly up a steep hill in OD with full lock up (ca 800RPM going 50mph) at part throttle, and the engine runs smooth and quiet. Other times I will have to downshift to 3rd and give it half throttle or more to climb even a slight gradient.

The seemingly random and intermittent nature of the problem made me think it might be the charcoal vapor "space station" in front of the carb. Maybe it would open and feed the engine too much gas if the canister was soaked. So I disconnected and plugged all hoses going to and from this apparatus. No difference what so ever. It did not occur to me to try the same thing with the EGR, but AFAIK this should not have that much of an effect on AFR.

Now, the thing is, on this trip I also noticed something wierd. Sometimes, I would have the same problem going down hill. That is to say, it I let off the throttle the car would slow down quite badly going down a hill. Which has caused me to think maybe it could also have something to do with my brakes. Maybe they get stuck while braking? I recently changed the spring in the prop valve as I have C5 brakes in front. Before the new spring the rear wheels wouldn't stop spinning with wheels off the ground and brake pedal floored.
I can't imagine the engine or transmission slowing the car down that much going down hill. Especially when it doesn't do it all the time.

Before setting off on the trip I had the car on jacks, and found that if I turned either rear wheel, the opposite wheel would rotate the same direction. I know the diff isn't in perfect working condition, as I get the classic singing noice from it when coasting or cruising at around 40 mph. But my logic tells me that if the diff is cauing trouble, it would be constant, not intermittent. Thoughts?

A last thing to note, when I did set the timing, my dad rotated the dist slowly while I watched the timing mark. It would increase steady and linear from 0* up to 8*, but turn it slightly up from there and the timing mark would jump off the scale. I did disconnect the EST or ESC or whatever it is called. The single orange wire coming from the battery running along the passenger frame.
Now, I set the timing at 8* where it was steady, but what if while driving it jumps up like I saw when I set it? Would that cause symptoms like that? Or maybe I should set it higher, and the symptoms occur when the timing isn't jumped?

There are just so many thoughts flying through my head about this problem, so sorry if this post seems like a big incoherent rant. I just had to get all the information written down. I would really like to figure this out soon. If not I might have to cancel my Nürburgring road trip this summer. I will not drive the car on the autobahn in its current condition.

Last thing to note, even with all the problems it did average 24 mpg on the trip, but I am sure it can do much better. Just after I rebuilt the engine in 2010 it did 26 mpg.

Thank you for any and all advice.
If you need more information about the car or how I have set it up and/or adjusted things on it, please don't hesitate to ask.
- Dennis

Mayt13

I'm not sure this is an engine issue. If your motor is working harder (making more noise), and there is still no improvement in your power output, it may be that your driveline is not doing its job getting that power to the ground. Maybe your torque converter is slipping? I can Imagine how that might cause the Trans to shift to inappropriatly high gears on gradients .

Disclaimer: I don't work on carburetors or automatics

Edit: in a given gear, do your RPMs rise or fall when this issue occurs.
Rise=>Trans issue
Fall=> Air/Fuel/Spark/Timing issue

87_LG4

RPM is the same when the issue occurs as when it operates normally. Then, as the speed drops, the RPMs naturally drops as well. Thing is, when the problem is in effect, it hardly matters what RPMs im getting. If I drive up a hill at 50 mph in OD with lock up, my RPMs will be around 800. If I then change to 3rd gear, they will rise to about 1500, but the engine will still struggle. If I didn't know better (which obviously I don't) I woud say it sounds and/or acts like it isn't firing on all cylinders.

I tried to get some gopro footage on the trip to document the issue, but you can't really hear anything on the video as the mic is peaking all the time, so I only got distorted sounds. But if I can get my hands on an external mic, I will mount the camera back up and get some better footage. Maybe that will help.

Oh, I just thought of something else. Sometimes, the car will stumble and bog down when I'm at a stand still and give it a little gas to get going. Just when I put my foot down it almost stalls and then it goes. Not sure if its related or not, but it is intermittent as well.

87_LG4

So I'm pretty sure now that my in-tank fuel pump is no longer working. As far as I can tell it doesn't prime when I turn on the ignition. I tried shorting the fuel pump oil pressure sensor. Still nothing. I also checked all the fuses, but they were good. I didn't get as far as checking the fuel pump relay, as it is getting late (also, I'm not quite sure which it is and which wires to short/ground).

So if it turns out that my pump is dead, which part number would be correct for my 87 LG4? I think I've managed to narrow it down to either the EP86 or EP386 part number.

As far as I can tell, the only difference is the electrical connector. The EP86 seems to have two of the old push-on connectors, where as the EP386 has a two-pin click-type connector. I've seen some of the EP386 pumps come with a female connector that you splice with the existing wires.

Does anyone know which one I need? I don't want to start splicing wires if I don't have to.



Also, on an unrelated note (well, unrelated to the fuel pump at least) there is a noticable valve train noice coming from the rear cylinders, mostly on the passenger side. I guess it must be the rocker arms that need adjusting. I'm guessing this won't have much to say on the intermittent problem, as they usually don't fall in and out of adjustment. But in what way, if any, does it affect my engines performance and/or mileage?

87_LG4

Or how about this?
Looks like it's got it all

87_LG4

While waiting for the electric pump to arrive, I changed the mechanical pump as well. Now the engine starts quicker than it did before. I used to have to crank it for at least 15 seconds, and it would stall the first two or three times I put it in drive, before it would go.

When I was changing it, I noticed that one of the bolt holes in the front of the engine is open. I belive I have read somewhere that this hole goes through, into the space where the fuel pump lever is, which connects to the crank house. Obviously this isn't good, but how bad is it?

eseibel67

That hole is very bad because it goes into the crankcase where the PCV will be sucking dirt into that hole. Get a bolt into it right away. Put some thread sealer on it as well. The surprising thing is that it doesn't look like it's been leaking oil. Make sure that the bolt you put in it is short so it won't interfere with the fuel pump rod.

As far as your main problem, you very nice job of explaining it clearly. Hopefully the fuel pump fixes it.

87_LG4

The bolt hole at the front of the block doesn't seem to go anywhere. I tried to get my camera down there, but it was too cramped. So I took a q-tip and probed around in there. It felt to me like it bottomed out about half an inch or so in, and there was no oil or anything on the cotton. I guess maybe they plugged that hole on roller blocks.



Regarding my actual problem, I have now replaced the front and rear fuel pump. The new electric pump works when I jump the fuel pump oil pressure switch, or the relay. But when I turn the ignition on, the signal voltage to the relay is in the millivolt range. In other words, the electric pump will only run if the oil pressure switch actually works. As it stands right now, the new pumps have not resolved my problem. This would all be so much easier if I could monitor every last little thing on my car at all times, like throttle position, transmission pressure, fuel pressure, duty cycle, brake temperature, O2 readings, spark control, etc etc...

Question now is, why is the signal voltage to the fuel pump relay so low? Where do the two wires come from?

87_LG4

Short update. Drove the car back home again. 450 miles. Best measured fuel consuption was a little over 27 mpg. Also, it threw a code 44, aka lean mixture. Me thinks the problem is not air/fuel related, as the symptom has been present before, when the mixture was measured at 11:1, and now, when apparently it is lean. Which leaves me with, what, timing? It is set at 8* advanced, which was a bit better than the previous 0* and subsequent 4* and 6*. I might just keep advancing it and see where it goes. I don't remember if I have mentioned this before, but when cruising the rpms (7-800) are only a little bit more than when idling (~600), which would mean that the timing is what, maybe 10* advanced when cruising (not adjusted for spark control). But can my car benefit from a more advanced timing when I crusie at such low rpms? Also, there is the problem that i mentioned before where the timing will jump a fair leap on the timing scale when I advance it just beyond 8*. Don't know what that is all about.

naf

iTrader: (7)

Setting timing: The Ignition Control Module has a built in timing step increase that will bump the timing up at around 1000 rpm. Keeps it driveable if the ECM fails to control timing. This is likely what you're seeing when advancing it and is perfectly normal.

Increasing the base timing above 4 or 6 can be counter productive. The Knock Sensor can over compensate and pull more timing back out. Best to experiment with different timing settings and compare mileage.

Intermittent loss of power like you describe can sometimes be caused by a failing catalytic converter. The converter guts rust out and blow around in there occasionally causing a restriction. A restricted exhaust can still allow good mileage at cruise when demand is light. Try disconnecting the cat.

I'd look for a vacuum leak in response to the lean mixture code. Potentially unrelated to your original problem.

Oh. If you're getting 24+ miles per gallon and your dwell readings are good, your mixture is NOT at 10/11:1. MPG is the best indicator of an efficiently tuned motor/vehicle combo.

87_LG4

I'll try to experiment a bit with timing.

Regarding the cat, I don't have one anymore. I've got the Hooker 2055 and the Aerochamber cat back to go with it. Shouldn't be any restrictions there

I'll see if I can't hook up a vacuum gauge somewhere in or on my dash. I've got a GoPro as well now, so I'm gonna see if I can't get some footage of it all.

Regarding the mixture, I got those numbers from my dyno sheet last August. I asked the guy if that might be caused by my secondary rods and hanger (CK/G I think), but he told me that it was running rich at part throttle as well. Now I have done pretty much all I can do to tune the carb according to the books, as per my first post. Only thing I haven't replaced is the MCS, but it clicks at IGN, and the ohm measured was 20, so all signs point to that being good.

I have attached the dyno sheet, and I'll post a link to a video of the dyno run as soon as they are uploaded. Note the black and blue smoke while at WOT.

87 Camaro DYNOmite.pdf

naf

iTrader: (7)

A member had an issue with running rich with correct dwell in the past and chased it down to a vacuum leak within the accessory system coming off of the port on the manifold behind the carb. We surmised that the leak may have been affecting one bank of cylinders more than the other and although the O2 was happy the opposite bank may have been rich. You can use a 'mityvac' or similar device to apply vacuum to this system and check.

As the secondaries kick in the ECM loses control over the mixture, as you're aware.

If you've done the work to the carb since the dyno, I'd expect that you're good now though. Especially considering your excellent mileage (US gallon, I assume?).

naf

iTrader: (7)

It may also be prudent to have your transmission checked by a professional.

87_LG4

Could be a vaccum leak there. I know that my HVAC unit has the classic hissing sound indicating a leak. I'll try to plug as many vacuum ports as I can from the carb and manifold, and then reconnecting the one at a time.

As far as MPG conversion, I'll just go ahead and call it Google gallons I just used Google to convert it for me, but I forgot to check if it did US or UK or whichever. In metric consuption it did 8.61 liters per 100km (if anyone wants to double check that number).

87_LG4

The transmission was completely rebuilt in 2012 by a company (the only company as far as I know) around here that does automatic transmissions. Prices around here for a job like that are insane. I paid around 30000 NOK for it, which is around 4800 USD. This is the list of upgrades he sent me:

3-4 clutchpackage z-pack.
Corvette 1-2 servo.
The Beast 2\4 shell.
13-winged oilpump.
Re-enforced converter.
New 4l65e planetgear including needlebearings.
BorgWarner clutches.
Steel pistons in forward\coast\3\4clutch.
Transgo shiftkit.
472" boostvalve.
286" boostvalve revers.
New bearings\seals\etc.

He figured it should be good for up to 400 horses

Also, they put on a transmission cooler

naf

iTrader: (7)

27 MPG

For what you paid for the transmission work, they should be willing to put it on a lift and have a look at the line pressures. I'm leaning towards transmission, especially after re-reading and noting the lack of downshift.

87_LG4

It propably should be said that even with the carb rebuilt by the book, I do still get hesitation when I give it a little gas from a stand still, like at intersections and what not. It sputters for a second before it goes. Is this relevant? Also, in any case, how do I fix it?

87_LG4

I had a long post going on about what happened when my tranny got rebuilt, but my browser decided to crash. Long story short, they botched it the first time around, and spent a total of two months on it, partly because they didn't realize that my tranny was from a truck.

It probably is the transmission. I will call them first thing in the morning about the line pressure, but I do not trust them to take out the tranny and have it fixed before I'm going to Germany in two weeks.

87_LG4

I've decided I can't deal with the transmission people right now. Mainly because I'm about to install a TrueTrac in my rear end, so I have enough on my mind. Pluss, I can't exactly drive out there now, with the rear end pulled off the car

I've got the rear end out of the car, and the old carrier out of the diff. Now here is something to note. First off, the pinion nut was not tight, like at all. Secondly, after I removed the carrier and started cleaning in there i discovered a hole in the rear end. Looks factory, but what do I know. There was nothing to plug this hole with! Anyone seen this before? What and/or why?

naf

iTrader: (7)

Can't help on the rear end.

On your trans issue though, I'd recommend checking the condition of your TV cable. A stretched or failing cable may cause some issues similar to yours. It may seem to be adjusted but may not be moving the valve properly.

87_LG4

I did read up on that a while back. Can't remember it all, but at the time I had a clear image of how it worked, and how to set it properly, which I believe I did. But I also recall something about needing the valve itself to be set properly by the installer (in this case the transmission people) before the cable adjustment could be made. ****, now that I think about it, he did mention something about a kick down wire being out of adjustment when I first got it back (took two more tries for them to get it to where it is now). I hope that guy didn't actually think it was just a kick down wire.

Man, I'm getting all worked up over this. Can't stress out when I'm about to install a fresh new LSD and gears. I don't want to rush this job to say the least.

So, if anyone else knows anything about the hole in the differential, please let me know.
Thank you

naf

iTrader: (7)

Peruse:

www.tvmadeez.com

87_LG4

That's it! Couldn't for the life of me remember where I had read about it. Thanks, I'll have a look see, maybe I missed something last time.

But back to the rear end. Up untill now, I was pretty sure I had an open diff, as it would spin one tire, never grip etc. But mine has a bunch of springs holding plates together between the spider gears. Does that mean I actually had (obvoiusly not working anymore) a posi diff?

naf

iTrader: (7)

Yes. I'm told the parts needed to rebuild it are not available though.

sofakingdom

iTrader: (1)

Yes, that is an Auburn posi; probably stock; probably not doing anything anymore. Those aren't known for durability or longevity. And naf is right, they are not repairable. Time to chunk it and get something good.

The hole in the diff pumpkin is the vent. There's supposed to be a ... vent ... stuck in it.

87_LG4

Guess I need to find a new vent then.

I allready have a brand new Detroit TrueTrac with 3.42 gears from Yukon waiting to go in.
Thanks for the quick reply

87_LG4

PO must have changed it at some point. My RPO sheet does not list G80, only GU2 (2.73 ratio), which is correct according to the 41:15 numbers stamped on the ring and pinion.

Regarding the vent, I found some pictures of it while looking up the original part number (GM 1236317). Looks to me like its just a sort of breather with a cap on it to prevent foreign materials from entering. Suppose I could replace that with anything suitable. Or is it more sophisticated than it looks?



EDIT: Forgot to mention, the reason I am fairly certain that the PO installed an Auburn posi, as opposed to replaced the entire rear end with a factory installed posi, is bacause of the fact that I pulled the inner pinion bearing off with my hands! No tools required! That can't be normal and/or good.

The mechanical state of this car never ceases to amaze me...

EDIT 2: Apparently, only G80 rear ends came with a factory magnet installed, which mine has. So, maybe PO did swap the entire rear end. My RPO sheet does not list G80 and the chassis number on that sheet matches the car.

sofakingdom

iTrader: (1)

That looks exactly right; nothing real elaborate.

I'd suggest putting the right thing back in there though. Can't cost much, or alternatively, snag one at yer local buzzard nest. That'd be a lot smarter than something that might fail and let the fluid all get flung out again. The inside of a rear is a pretty violent environment after all.

87_LG4

Quick update:

Got the Truetrac in, and set it up to where I think it might be close. What do you think? The installation instruction that came with the Yukon stuff tells me that this is an acceptable pattern, but the examples that they deem acceptable vary quite a bit.

Backlash is at 0.007". All the preloads are set as well.







I hope this is a good pattern, but this is my first rear end rebuild so I have no idea what is within range and what can improved.

87_LG4

Long time since last post.

Since then I've driven the car with the new rear to Germany and back. That was a great trip, apart from the fact that I didn't have time to change the speedo gears before I set off, so my speedo was useless, and my odometer added a few extra miles so to speak.

The symptoms were still there, but they were less noticable what with the engine working at higher revs.

I am however completely convinced now that it is the transmission that is the culprit. After the summer holiday I drove back north to where I go to college. Half way there the speedo stops working. And what does the speedo have to do with the transmission you ask? The torque converter lock up is the answer. VSS tells ECM how fast we are going, ECM tells lock up to engage/disengage at a certain speed (Please correct me if this is wrong). No VSS signal, no lock up. None of theru old symptoms are present now.
When I first noticed it, it was like driving an entirely different car. The engine revved smooth, and when I tried to accelerate it actually would, and without the heavy work noice and rumbling and overall fstration that came with it. Smooth acceleration and no problem going up hills.

Now, thing is, this is obviously not how the car is supposed to work. It should work fine even with a functional lock up. So what is wrong with my transmission that would put such a heavy load on the engine with lock up engaged?
Another thing that I am not sure about: Is the lock up supposed disengage going up hill as soon as i give it a little throttle? Or will it stay engaged untill speed drops below a certain point no matter what?

naf

iTrader: (7)

The lock up will engage when the ECM sees a constant speed, load and throttle position. It is normal for it to unlock when load increases and subsequently the throttle increases when going up hill. It should, however, be able to accept some light throttle and increased load before unlocking.

If small changes in throttle cause it to unlock immediately, I'd check the TPS. A common failure of the TPS is to send erratic changes in voltage to the ECM with small changes in throttle position. A bad TPS can also send a near constant voltage to the ECM under different throttle positions which can delay normal converter unlock under load. In my experience problems with the lock up, when it works but not correctly, have usually been traced to a bad TPS.

You can backprobe the B and C (middle and lower) pins on the TPS connector with a voltmeter and with the engine 'on' (doesn't have to be running), you should be able to measure around 0.40 volts at idle and around 4.0 volts at WOT AND it should vary somewhat linearly between the two extremes.


Before whipping out the meter double check that the little pushrod is in place beneath the lever arm for the booster pump and that the booster pump is actuating correctly with throttle.

I don't expect this is the final answer but you should rule it out. Sounds like a large part of your problem may be a lock up that doesn't want to disengage. It may be worthwhile to run it with a scanner hooked up and see what the ECM sees.