Building an LN3 from spare parts plus a Supercharger

[DAVES89]

Interesting evaluation 2seater. As most of the "old timers" know I have always wanted a super charged setup but never did it. However with your [and Ronnie's] advice I did have an engine rebuilt with the '88 cam as well as higher compression pistons [and some porting of the exhaust manifolds which gets me to about 190 HP. No idea of the increased tq though [maybe you have input on that].

 What we should do after you have your car dialed in a bit better is do a "time trial" on a large parking lot to see how we compare. If that isn't a good idea, just you driving my car to do a "seat of the pants comparison".

 I am glad I bought that 5000 mile '88 engine to get the cam and then did the rebuild with the 9 to 1 compression pistons, the car is way more responsive, runs on regular gas, no change to the prom and doesn't overtax the transmission.

 And one last thing, the gas mileage is about the same, which makes me wonder how much HP these transmissions can really take before they blow out. I think the Buick engineers might have been a bit conservative unless they really designed the car to be a touring car with no plans for higher performance.

Edited July 8, 2022 by DAVES89

[2seater]

I drove the car to my cottage today, only a trip of 50miles and mostly highway but another observation as I accumulate some time with this combination:

 

Cold start is still a little rough. It starts fine, but seems to have a bit of trouble finding a good idle at first. It drops low and stays there a bit before recovering. Essentially, open loop needs some attention. I am using all of the items attached to the throttle body as it came on the donor engine. The TPS, MAF and IAC are all as purchased. I did clean things up and examine them before assembly, and they all work just fine in closed loop. It's possible the injectors I installed aren't quite up to par, Bosch 30# Type 3? Will get that sorted eventually.

 

I am warming up to the way it drives and responds. There is no question that a turbocharged engine of this type will make more power but that isn't the end all and be all. It is a smooth and relaxed cruiser and in the gently rolling area I drive through, it grunts its way up small hills without apparent effort. I did disconnect the vacuum from the supercharger bypass to force all air to go through the rotors but in my limited part throttle I noted little benefit. One thing that is maybe related which I described above and that is the vacuum bypass for the s/c. It doesn't shut off air to the actual rotors in the s/c, it just opens an additional passage which routes air to below the s/c, essentially two parallel paths. I applied vacuum to the bypass cannister, and it just starts to open at 5" of vacuum and is fully open at 12". Funny how those levels are right in the range I see when driving normally; 5"Hg and accelerating the bypass is almost completely closed and 10-12" at 65mph cruise is completely open. Almost like GM planned it, imagine that.

 

My code E026c is back, so I believe it probably has to do with the EGR which is non-existent. No other current codes. The A/C works perfectly, the cooling fans do as well. TCC, cannister purge and cruise control all work as designed. One last thing, the exhaust barks a fair amount. I do run a replacement cat but also a straight through muffler, which worked well with the turbocharger taking the edge off, but it is a bit noisy now. I don't know if it is enhanced by the modified rear manifold where cylinders #2 & #4 are mostly isolated from the front cylinders plus #6 exhaust flow. The O2 sensor is located right at the point where the flows merge to exit. Maybe the natural turbulence from the stock interference design would be quieter?

[Ronnie]

1 hour ago, 2seater said:

Cold start is still a little rough. It starts fine, but seems to have a bit of trouble finding a good idle at first. It drops low and stays there a bit before recovering.

What about after it being driven and the engine is warm? Does it do the same thing on a restart if it has been sitting for a while but still warm?

[2seater]

2 hours ago, Ronnie said:

What about after it being driven and the engine is warm? Does it do the same thing on a restart if it has been sitting for a while but still warm?

No issues on a restart. Warm or hot, it seems perfectly happy. Now that I think about it, I should put a gauge on the fuel rail to see if that may have any bearing.

[2seater]

I was curious since I was asked the question. I went out, connected a gauge and tried my normal start. I don't wait for a prime, I simply turn the key and it fired right up and idled normally. It had been sitting for 6 or 7 hours at the time. It is inside but ambient in the parking area is 68deg. Fuel pressure is rock steady at 35psi unless the throttle is blipped where it jumps over 40. It looks normal to me. The one item I did note trying to snap the throttle is it doesn't like it from low rpm or idle. A short jab will bog, even after fairly warm. Jab the throttle and hold it, it will cough somewhere internally and then recover and accelerate. A lean bog, like low float level on a carb?? OR, does it want more timing down low? The same chip that is installed now, using the s/c timing tables, was tried with the previous engine with the turbocharger. The injectors are a different brand, Accel, but are also 30# rating in the turbo engine so the fueling in the chip is correct for both engines. The one item that was noticed, and I posted it previously, was the engine just wouldn't accelerate and simply laid there until it gained a bit of rpm then it would go. The turbo engine had none of those symptoms prior to changing the chip, and the chip was an exact copy save for the timing tables. Something to examine when I get home.

[Ronnie]

44 minutes ago, 2seater said:

A lean bog, like low float level on a carb?? OR, does it want more timing down low?

Or more like a bad or misadjusted spray pump on a carb.

 

I wonder what is responsible for enriching the mixture on the 3800 fuel injection when you hit the throttle quickly? My guess would be the fuel pressure regulator and/or the MAF sensor since the 3800 doesn't have a MAP sensor as far as I know.. Could the regulator or MAF sensor you have on your engine be different from the one used on the SC engines?

[2seater]

All good questions. There are enrichment tables in the chip to mimic accelerator pump action but have never adjusted them before. The throttle body/MAF combination looks exactly like the TPI version from the 91 L27 but is much larger. I have noted in the past that the stock LN3 throttle body that I had modified, bored and larger throttle blade installed, does cause a hesitation when the throttle is cracked. It isn’t a problem but it is there. This throttle is much larger yet. 
There is no MAP sensor on my engine but I do believe there is one on a stock 95 s/c engine. My ECM has no input for this so it must be worked around. It would also be used for boost sensing to control the bypass valve. The factory GN engines used both MAF and a 2bar MAP sensor for similar reasons. 
The MAF sensor is the same style as used on the L27 TPI engine. I haven’t compared its calibration in depth but the flow indications I have seen look pretty much normal. It is something to look at to see if there is a big hole in the flow progression with increased throttle.

The pressure regulator is new and is the same style as used on the L27. When I did the original disassembly I noted the regulator was slightly lower pressure rated, like 2.8bar or something like that, and I installed a 3bar like used on my other engines just because all the different injectors I have are flow rated at 3bar and I didn’t want that variable. 

[2seater]

This has me a bit confused but is another data point to be examined. Car sat overnight, ambient temperature of 52degF. It starts instantly with a somewhat elevated idle, but smooth. No idle issues at all but only waited 15-20seconds and tried blipping the throttle while definitely in open loop and it responds immediately. No bog, hesitation or any other bad behavior. I didn't let it warm up, or try anything else, but it indicated to me that it is capable of snappy response, so the system is capable. Maybe too snappy. That's how you hurt parts 🙄

[Ronnie]

A couple of trial & error things come to mind that I would  try to isolate the cause of the problem.

 

When the engine is warm and bogging when you blip the throttle, disconnect the vacuum line from the regulator so it has max pressure all the time. If that improves the bogging there could be a lag between the engine vacuum dropping and the regulator raising the pressure quickly enough causing a lean condition. If it does improve the bogging you might want to check to make sure you are using the correct vacuum port for a SC engine and make sure you have the correct regulator. for an SC engine.

 

Next, try disconnecting the O2 sensor to put it back in open loop with it operating off the tables. If that improves the bogging it might point to the MAF causing it, or you might need to adjust the tables to eliminate the bogging in closed loop. You don't want to get it so rich that it might wash the cylinder walls but I would rather have a rich mixture than a lean mixture. Lean mixtures can destroy high performance engines.

 

Yeah, I know, this is carport engineering at it's finest but you have to start somewhere. 🙂

[2seater]

I tried the suggestions this morning. Cold start is no problem at all but after 30 sec or so the idle drops to stall speed but it never does stall. It recovers after just a few seconds and then seems to idle normally but the transitions to lower rpm as it warms is not smooth. I think the IAC may need attention. Blipping the throttle is very responsive until it gets a little heat in it, at about 9 o'clock on the gauge, and then the bog occurs. Raising fuel pressure had no effect, ditto for disconnecting the O2 sensor. It takes up to a minute for the ECM to indicate open loop and stop showing cross counts? In any case, it made no difference in the off idle bog. I did try disconnecting the MAF and it immediately quit, it will start momentarily with it disconnected but quits almost immediately. It will not run without the MAF connected? Not sure what to make of that?

[Ronnie]

The IAC might be causing the erratic idle. You are over my head on the bogging situation. In the video below you can see it is possible for the SC engine to respond quickly to blipping the throttle when you get it dialed in. I wish my 3800 would rev like that. I don't see what I was expecting when I look at the throttle body where the MAF should be. Looks like there is some kind of rod sticking up. Is the MAF different on a SC engine?

 

 

[2seater]

Nice looking car from a few years ago. I think that car was recently on Facebook with a blown trans? Mine does sound like that also. When it is “on”, it is super snappy, the calling card of a supercharger. I am not sure what rod you might be seeing except for what looks like an air temperature sensor in front of the t/b? The throttle body and MAF is in a single casting, very much like the L27 tuned port style, but larger.

I am back home so I looked through the programming of the chip. There is a spark advance modifier vs temperature but it is at either very low or very high temperatures, so that is unlikely the cause. I did find, two tables for quasi accelerator pump action, one in park/neutral and one in drive, and they are similar but different. I hadn’t mentioned it earlier, but the bog is not as bad under load in drive, where you would think it would be worse. To cut to the chase, the temperature where the “shot” drops in half is at 37degC in park. I increased and extended the pump shot in both park and drive, drive being larger to begin with. I will burn a chip when I get the chance. 

[Ronnie]

What am I seeing that the red arrow is pointing to?  Maybe something to do with the throttle cable bracket and it just appears to me like it comes from the MAF sensor? Will be interesting to see what the changes to the chip programming will make. Keep notes on what you do. 🙂 

 

[2seater]

It is part of the casting that is tapped for the screw that holds the cable bracket at the forward end.

[2seater]

Well, something happened in the last 16hrs. I burned the new chip, the car started and ran pretty rough. A little black smoke from the exhaust and I think, maybe I screwed something up in the new chip. I switch back and it runs the same, rough, cooling fans are on and I notice there is no rpm or temperature indications, hmmm. I am pretty sure it is running in limp made. I try diagnostics and it says "no E data". I go to disconnect the battery to hopefully start everything over and there is a mouse sitting on my battery😖 I pulled the panel under the passenger's side dash but no evidence of a nest or chewed wires. The cover is on the ALDL. I don't know if all the engine data comes through the ecm or quite what to think. I do have another ecm or my other thought might be the special socket that was installed for replaceable chips has maybe lost a connection? It is warm and humid, plus I have many other things to do, but I could use suggestions when I do get back to it. I will also consult the FSM when I get time as well. 

[Ronnie]

36 minutes ago, 2seater said:

I don't know if all the engine data comes through the ecm or quite what to think.

I think the BCM is responsible for sending information from the ECM to the IPC. But, I don't think the BCM would effect how the engine is running. I would change the ECM and try again to see if it clears up the problem. I know nothing about the special socket you speak of. Could it have got damaged during the chip swap?

[2seater]

I believe you are correct about the display of data but it seems more is going on?

 

This is a Zero Insertion Force, or ZIF socket. The silver thing in the upper left is a lever. Lift the lever and the spaces open up for the pins of a chip, which is of the 28 pin variety, a 256k in our case. Ryan at GM Tuners modified a memcal with a similar socket so I can just change and modify easily obtained chips rather than doing so to the memcal over and over. Once determined that the changes are what you want, burn in into a memcal and install that. There is essentially no force involved but maybe a solder joint or something let go??

[Ronnie]

Do all the other BCM controlled things work, like the climate controls and interior lights?

[2seater]

Well, it appears something in the modified Memcal has gone astray. I swapped in my spare ECM including a stock type Memcal that had a turbo program in it from Ryan. This was mostly a test to see if the communications problem went away, and it did. Tach, coolant temperature, normal idle, no cooling fans, etc....all good. No "E" codes in diagnostics either. Yay! I left the ECM in place and transferred the modified socket Memcal back in place and the tach and coolant temperature did not display. I didn't look for other things, I just shut down, and swapped the stock type back in, and everything came back. Now I am in a bit of a conundrum; do I see about having another Memcal modified for the switchable chip, or reprogram one of the two previously tuned Memcals I have? At least I know where problem lies👍

[Ronnie]

Glad you found it. That proved the BCM isn't the problem. Don't have any advice on what to do about it. It's a little bit over my head.