87_LG4

So today I dyno'ed my car, which is something I've wanted to do ever since I rebuilt the engine. I should perhaps add that I got my car dyno'ed by this guy, so I'm pretty confident that the results he found are accurate.

Now I'm just gonna post as many details as I can about my engine so it'll be easier to figure out whats wrong.

It's an LG4. I still have the original Q-jet which has been rebuilt. The engine is a 305 with ported 081 heads. I put a Comp Cam XR258HR-10 in it. I have an L69 dual snorkel intake. I have adjusted the carb according to all the specs I could find here on this site. I've changed the secondary rods/hangers, it now has a G-hanger and either CC, CK or CE rods. I have adjusted the MCS to 30* dwell on the 6-cylinder scale. I have adjusted the float according to the rebuild sheet. TPS is adjusted properly. IAB has been adjusted. I've got Hooker 2055 headers, 3" all the way back to a Hooker Aerochamber muffler, with no cat. All the AIR stuff has been removed and plugged by PO. EGR is still there, alive and kicking. I've installed a heated O2 sensor.

Now on to the dyno results:

87 Camaro DYNOmite.pdf

So apparently, my AF starts at around 10:1 and ends up at around 12:1! According to Paal-Arvid (the dyno guy) the rich mixture costs me an estimated 75 ft lb of torque at the start of the scale. That's a lot!

What could cause this? How do I fix it?
I remember reading something about JB-welding the underside of the Q-jet as it is prone to fuel leakage. Could a potential leak drop my AF that much?

Any and all help is appreciated.

-Dennis

87_LG4

Anyone?

I find it strange that it should be so rich under WOT operation. As far as i know, the secondaries are what provide most of the fuel and air when you punch the throttle, and that part of the carb is not computer controlled. Given that, it would seem logical to me to rule out the IAB, TPS and MCS as culprits. Again, as far as I know (which isn't much I'll admit, so please correct me if I'm wrong) the secondaries are subject to the forces of vacuum. So if there is a vacuum leak, this would affect their performance. I would try to measure the engines vacuum, but I'm not quite sure what to look for. So if any of you could point me in the right direction as to where I should get my readings from and what they should be under normal and WOT conditions I would greatly appreciate it.

Thank you

-Dennis

Ozz1967

iTrader: (4)

NAF or Aperion and Five7kid would be the people I'd send a PM to regarding your issue.

Damon

All those rods you listed are pretty rich for a little 305. Have you considered using a set of DR rods, like came originally in the L69 HO motor instead?

87_LG4

Honestly, I bought the rods that were recommended in the "Tuning for Performance" tech article. It lists CK as a good all around set that are marginally richer then the L69 rods. But now that you mention it, the article does not specify engine size, so for all i know the CK might be better suited for a 350+ engine.

But if you think I should consider going down a size or two in rods then I'll definately have to check that out.

Damon

Certainly worth a shot. I have 3 sets of rods that are my go-to choices for starting a tune. DP (lean), DR (middle-of-the-road) and DA (rich). ALL of them are rich on initial opening, which almost every performance-oriented QJet appreciates, differing almost entirely in tip diameter only.

87_LG4

I'll have to get me some of those rods then

But there is one other thing that I just remembered. The dynotech guy told me that my car was running rich on the primaries as well as the secondaries. How that came to be I do not know and I don't know what more I can adjust to make it run as it should.

paul_huryk

The dyno shows how much power can be left on the table when your a/f ratio is off by a large amount - important data for those who think carb tuning is a 3rd class citizen.

I personally have about 12 sets of rods and just as many hangars to tune q-jet secondaries. Even with a "regular" (non wide band) A/F gauge, I picked up 35hp by changing the rods & hangars to get it dead on - and it wasn't all that far off in actuality.

In the past, I have been witness to motors that should have been 400+hp if tuned right, but put out under 300hp due to tuning, wrong exhaust, and inadequate fuel systems (OEM block pump instead of an electric in/near the tank).

87_LG4

I wrote a long post just now, but my web browser crashed and now it's gone.

Quick recap:

Replaced entire distributor, coil, plugs and wires since last time. Set timing at 0*.
Found out engine might be running too cold, making the ECM richen the fuel mix. (stat stuck open, 165 degree fan switch)
I used to have an EFE valve. Now it's gone, but the vacuum line for it was still plugged in to the carb. I'll be replacing and/or capping ALL vacuum lines.
After this has been done I'll check dwell and all that again.

Hopefully all this will also fix my highway cruise problems. (Intermittent lock up, engine working VERY hard under moderate load, like small hills). I've been told the lock up is controlled by the ECU based on vacuum and temperature. Is this correct?

I'll try to fix all of the above before Wednesday next week, as I'll be driving 500 miles across Norway before winter sets in.

- Dennis

87_LG4

So I bought a vacuum gauge and I just drove a 20 mile stretch of highway. Up a slight hill doing 50 in OD with the torque converter locked up I got as low as 3 inches Hg. At that point I really had to push the throttle to not slow down. At idle it gets between 17 and 18 inches, with a slight fluctuation (park). Even less in drive. So I'm guessing this has gone from being an adjustment problem to being an internal engine problem. Am I correct in saying so?

JaBoT

The low vacuum at part throttle could be more a timing issue. Bigger cams like more timing down low and while cruising, unfortunately you cant really do anything about it with the computer controlled distributor.
I doubt there is an internal engine issue considering it made over 400 lbs of torque at 3200 rpm.

87_LG4

So where should I set my timing when it held 800rpm@50mph? Right now it is 6º advanced. Honestly didnt think the cam was that big. And it hasnt always been like this.

JaBoT

No idea. The computer controls it. I guess you can try bumping it up till it knocks at wot then take a few degrees back out. That's about all you can do to get the most timing everywhere else without programing a new chip.
If it hasn't always been like this, then when did it start?

Yenipenny

I may have missed something in this thread, but if your car still has enough originality to be computer controlled, the stuck T-stat is a significant factor in the car running rich. During those years, the engine HAD to reach 186° in order to go into closed loop. If the engine temp is less than that, the computer thinks the car is still cold and will add more fuel.

87_LG4

That is quite high temp to reach before open loop. I put a 220 stat in it yesterday and it seems a bit better. I'm on the road now (pulled over as we speak, obviously) with around 400 miles to go. I'll try bumping the timing some, if only for the duration of the trip. I won't be doing any wot runs on it, so total advance won't be a factor. Have hardly reached 2000 rpm thus far on the trip at leadt

Yenipenny

Just to make sure our terminology is the same...the car stays in OPEN loop until it is warmed up to 186° F, then it goes into closed loop. There are some vehicles that go into closed loop at lower temps, but all GM V8s that I'm aware of go at 186.

Yikes! I didn't even know that they made a 220° tstat. The car came from the factory with a 195° tstat. None of the parts stores in this part of the country list a 220.

FWIW, during those years I was the Fixed Operations Director at a Chevy dealership. Although I was responsible for Body, Parts and Service, I spent most of my time directly involved with service issues.

87_LG4

Ok, so closed loop after it hits operating temperature. Got it might very well be 195ºF. I ordered a stock replacement for my year and it said something like 90ºC on it. Did the conversion in my head. I tried advancing the timing and that eeally helped I'll try fine tuning it along the way.

Yenipenny

Again, to be sure we are on the same page, the closed loop temp is NOT the same thing as the temp that opens the thermostat.

JaBoT

Just keep advancing the timing like I said untill it knocks at wot then back it off. It's the only way you can get any extra timing at low and part throttle with out reprogramming the chip or going to a non computer controlled carb and distributor.

Damon

The ECM can put the engine in closed loop at any temp over 100*F. Not sure where the higher numbers come from that I keep hear being thrown about.

The other thing that needs to happen is that the O2 sensor needs to start reading a certain number of "cross counts" so the ECM knows it's up to temp and it's reading can be relied on. This can be more problematic with a single wire non-heated O2 sensor like these cars came with from the factory. Often they will drop out of closed loop at idle (or never enter it if you just start it in the driveway and let it run a while).

There's a bunch of other little things that can prevent closed loop operation as well- most of which will show up with a "check engine" light on the dash.

Yenipenny

I'll have to respectfully disagree on the temp that the ECM goes in to closed loop on these cars. I've watched a few hundred GM vehicles, including Camaros, go into close loop at 186° on the CAMS machine and Sun Diagnostic Machine. I don't ever recall seeing the CL temp vary more than one degree either way. The 186° is why you can't use a 160° thermostat unless you get a custom flashed prom. The vehicle most likely would rarely ever go into closed loop.

Many later model vehicles will go into closed loop at lower temps by design, but I'm talking about 80s/early 90s. You are correct about flipping in/out of closed loop when idling due to the lower voltage of the O2 sensor as well a some other factors that affect going into closed loop.

Damon

Well, that's not the case with a factory prom. Not sure what I can tell you beyond that. I've put 160* stats in many 3rd gens (and other 80s-vintage GM cars) and driven around with the scan tool attached. They all go into closed loop if they are in good working condition.

If you read in the Doug Roe book about QJet carbs (the "bible" of QJets) under the computer controlled section it says that the ECM is capable of going into closed loop as low as 68*F. I've never seen it kick in below 100* myself personally, but it definitely doesn't need to be 186.

JaBoT

yea these cars go into closed loop way before 186. I think you may be confused as to why you had to get the matching chip for the 160 stat and fan switch. It has nothing to do with closed loop. It has to do with the coolant temp vs fuel enrichment table. Basically like a choke. At 160 it is still adding extra fuel because it thinks the car isn't fully warmed up, but it is still in closed loop. All the chip did is lower the temp it was still adding coolant based enrichment.

Fast355

iTrader: (2)

Agreed!!! My old G20 would not run hotter than 170°F in cool weather without blocking off the radiator with cardboard.

My 97 Express is in closed loop almost immediately regardless of coolant temps.

Yenipenny

Reading Chapter 6 of the 92 Camaro Factory Service Manual will help to understand this open/closed loop business on these cars. Especially read the info on Code 13 and a few pages past that.

QUOTE: My 97 Express is in closed loop almost immediately regardless of coolant temps.[/QUOTE/ I specifically addressed later model vehicles going into closed loop much sooner.

I'm done. Thanks for the discussion.

JaBoT

There is actually very easy to prove when it goes into closed loop without all this crazy discussion. Hook a scan tool up and drive the car. You will see that it will go into closed loop much earlier than 186 as long as the other sensors are working correctly.

Fast355

iTrader: (2)

Yes they will. My 83 G20 started life with an E4ME Q-Jet and had both TBI and TPI. With TPI it was in closed loop well under 100°F coolant temp. Heated 02 sensor really help the delay going into closed loop.

Fast355

iTrader: (2)

I have been datalogging and tuning these systems since 2002, no need to read the manual. I can open ANY STOCK calibration file and prove you wrong.