Need ECM guidance
 

My car has a stalling problem that's been driving me nuts for far too long now. Turn the car on after it's been sitting and it runs perfectly. No backfires, full power, flawless idle, and it will stay like that sometimes for hours. Then randomly the engine light will come on, the car will lose all power and start bucking and backfiring, then eventually stall. Only code showing is a code 44 which means it's running lean. There is no build up to the stalling though, it just randomly happens. Sometimes I'll stop for gas, or stop at a store where I only turn the car off for a minute, and when I start it again it runs like trash. Or I'll drive it for 8 hours and never have a hint of an issue.

The car has high km, and last summer I had a full tune up done, all sensors changed, as well as all intake gaskets. I'm 99.9% sure there are no vacuum leaks and as I said, it runs perfectly until it goes to s***. All of this started immediately after I did all of that work so l'm thinking that from a combination of age, sitting for a few years, and the big tune up, maybe the ECM is calling it quits. Now I need some guidance in regards to ordering a new ECM as I'm not very familiar with them. My car's a 91 LB9 GTA with a 5 speed and no modifications. Do I just order any LB9 ECM and keep the chip from my current one and swap it in to the new one? Or do I need to order the full shebang? Rookie questions I know, but I want to confirm before wasting money on the wrong part. Also, what's the best place to order from? Hawks seems to only have a used one.

Re: Need ECM guidance
 

Fuel pump could be going out, or the fuel filter is clogging.

As for an ECM, order the proper one (1227730) and swap the MEMCAL and small cover over to it.

RBob.

Re: Need ECM guidance
 

Both were replaced fairly recently, and if the pump were going, wouldn't it be more consistent? I drove the car one day for hours without a single sign of anything, then turned it off for maybe 2 minutes at a store, then when I started it again it instantly ran like trash. Had to let it sit for a few hours then it started back up and drove perfectly again. Also where would you suggest ordering from? I don't really want a cheap junk one, nor do I want a used one

Re: Need ECM guidance
 

Back in the summer of 2000 mine would inconsistently sputter and loose power. In the spring of 2001, before bringing it out of storage, I replaced the fuel filter and thought that the problem was fixed; however, it began to sputter occasionally a few weeks later. In spite of no codes being thrown (!), I checked vacuum lines, hoses, plenum for leaks around gaskets: anything and everything. I'll never forget the day that I replaced the fuel pump. (My wife was due with our second and he was born just after midnight: Sep 12, 2001.) I couldn't make it up the hill right by our house, so I limped it back into the garage and listened watched the news all day.

It was the fuel pump. It was inconsistent.

Re: Need ECM guidance
 

Is there a way to test it without dropping the tank? It's a Delco and it isn't even 2 years old, it's also odd that it would start doing this nonsense directly after I did a bunch of work as I don't see how anything could have been a trigger

Re: Need ECM guidance
 

ECM's can fail. It happens. I had a MAF ECM (7165) die on my car. You could tap in it and the engine ran differently - sometimes wouldn't even run. Smack it again and back to normal. Cracked circuit board I assume. Swapped it out and problem resolved.

You could install a wideband so you can see the actual AFR's. They are relatively cheap these days. I just put in the AEM x-series for my EBL tuning and it was less than $150.

Have the injectors been replaced? Sounds like they might be heat soaking when you stop the engine and possibly having coil failure. Check the resistance on them cold and hot. It shouldn't change. If it does they are shorting out when hot.

GD

Re: Need ECM guidance
 

I checked them the last time that I had an issue and they all seemed perfect. They were all replaced last summer from Southbay so I was hoping they weren't toast already haha. As for the ECM, I figured I'd replace it anyways because if it hasn't given up yet, at it's age it's only a matter of time. Where did you get you replacement from?

Re: Need ECM guidance
 

Re: Need ECM guidance
 

That's a good price too, I'm going to order it. Thank you! I haven't removed the ECM nor am I at the car so I can't see for myself, but is it literally just unplug/re-plug and go with the chip?

Re: Need ECM guidance
 

Re: Need ECM guidance
 

Ah yes if you have new injectors from SouthBay then I would doubt that is your problem. It is starting to sound a lot like the ECU may be at fault. You would really have to catch it acting badly and then try to hookup a scope to various inputs and outputs to see if you could narrow it down but being intermittent, and being the ECM is fairly inexpensive - I would just swap it and see what happens. Or go to something like the EBL system from RBob's DynamicEFI (that's what I'm running and it's excellent):

https://www.dynamicefi.com/

GD

Re: Need ECM guidance
 

Are you using that on a stock motor?? More out of curiosity. It would be a nice upgrade but probably something I'll leave for down the road a bit

Re: Need ECM guidance
 

It's a stock LB9 at the moment. The new 450 HP 350 is built but awaiting an intake from First Performance and injectors prior to installation. I upgraded the ECM in anticipation of the engine upgrade so that I might remove one more variable from the new engine startup. The stock ECM setup (mine was MAF) was really unsuitable for the new engine - the MAF was going to be a bottleneck so one way or another it had to be removed from the equation. The EBL was the most direct plug and play unit at the most affordable price. Time to setup and have it running was literally about 2 hours. Yours would be faster.

Also with SouthBay Bosch III's you will benefit from tuning even on a stock engine. With EBL this is very simple.

GD

Re: Need ECM guidance
 

You can test your fuel pump by taping the FPG gauge to the windshield, facing in the car and drive around the block. If you could do this while it is acting up it will help eliminate this from the equation.The pressure should be At 33psi @ idle and 43 at WOT give or take a couple pounds.

You said you did a full tune up. Did this include the ICM in the bottom of the dizzy? I only say this because I had a similar problem with similar issues, backfire, sputter and die, the inconsistency to be the big one. It ended up being the ICM. It took me a few weeks and a whole thread to finally find the culprit, I was sure it was fuel related and that turned out to not be the case..

Re: Need ECM guidance
 

I replaced the ICM as well but maybe it's faulty? I had it fail a while back and the symptoms were similar but not exact. With this current issue, I have a code 44 too which means lean exhaust, and I don't think that would come from an ICM issue. I plan on replacing the 02 sensor as well as I don't know if it's ever been changed. Maybe if it's faulty, it's sending the ECM totally wrong and random signals resulting in the lean issue? I would do your FPG suggestion but I can't drive the car for at least a few more months (Canada things) so I'm trying to narrow as much as possible ahead of time

Re: Need ECM guidance
 

Re: Need ECM guidance
 

Injectors are new and have been tested to not be the issue when the car acts up, I can't check until spring but I doubt it's the issue, not bad gas. I do have an exhaust leak at the bottom of the manifold (not where it meets the block) but I've had it for a long time and never had this issue so I can't imagine it's the culprit. Once that code has been triggered, will it ever reset on its own? I can start the car and pull that code even when it's running totally perfectly. The check engine light only comes on when the car starts to get sketchy

Re: Need ECM guidance
 

I can't check fuel pressure until the spring***

Re: Need ECM guidance
 

I had a somewhat different situation that turned out to be the ECM in my ‘89 TPI IROC which began to run very rich, surging, zero power, blowing smoke, stalling, fouling plugs and basically running like crap. The code I pulled was #45-o2 sensor RICH exhaust. The shop started out by checking fuel pressure which was good, injector leak down test was good, maf sensor good, o2 sensor good, injector ohm test good. (BTW the cts sensor was replaced due to corrosion by a different shop and also took apart the tank pressure valve and cleaned it) The shop also replaced the ignition module, but it didn’t remedy my problem. The shop manager called me one day and said he believed he had narrowed it down to the ECM and ordered an ECM for delivery. The replacement ECM turned out to be bad, so he ordered a second unit, installed it and problem solved. Apparently my faulty ECM was misreading a lean condition and responding by having the injectors pump more gas. A bad ECM can often lead you on a wild goose chase. HTH

Re: Need ECM guidance
 

That's exactly what brought me to originally assume ECM. Your situation sounds like it's exactly mine but rich instead of lean, though I imagine it can go either way. I'm excited to get the new ECM in and see how the car runs. In the few years I've owned it, it's given me so many issues that I have yet to drive it at it's peak potential. I really hope this gets me there haha

Re: Need ECM guidance
 

Have you checked the BLM's?

GD

Re: Need ECM guidance
 

What does that stand for??

Re: Need ECM guidance
 

Re: Need ECM guidance
 

I wasn't familiar with that but it seems that if it's showing wrong readings, it still points back to likely the 02 Sensor or the ECM no?

Re: Need ECM guidance
 

You should be watching the O2 voltage and the BLM's from the ALDL live data so you can determine if the ECM is at fault or it's recieving bad input data, or there is a mechanical reason for the issue.

GD

Re: Need ECM guidance
 

Re: Need ECM guidance
 

Maybe. It's not that simple actually. For example - a misfire condition drives the sensor lean (excessive unburned oxygen causes the sensor to go lean - the assumption is that insufficient fuel was delivered to combust all the oxygen), and this will cause the O2 sensor's voltage to drop, the ECM adds more fuel... but if the misfire is not resolved it doesn't change anything and you get a lean code eventually as the ECM is unable to bring the BLM's within an appropriate range.

GD

Re: Need ECM guidance
 

I want to tackle this so badly but unfortunately I'm still limited to what I can do in the garage until spring. I've never had the car act up without hours of driving so I doubt a reader would pick up anything conclusive with just a few minutes of idling

Re: Need ECM guidance
 

No - you need to have a reader with you at all times so you can whip it out when the trouble begins. But it would be useful to know where the BLM's are now with the Bosch III's. They tend to throw off the calibration quite a bit so it's probably already adding tons of fuel and I bet the BLM's are high. Many people report that without tuning for injector size and especially for injector latency and short pulse width values the Bosch III's run lean with BLM's up around 160 so the ECM is adding fuel all the time. It may be borderline till something else pushes it over the edge. You really need a custom chip or an actual tuning solution like the EBL if you are going to run them properly. People get away with it, but it's absolutely not correct to just throw them in and turn the key.

GD

Re: Need ECM guidance
 

I ordered the 19lb ones though, not the 24 as I wanted to avoid having to do any tuning. Do I need to get a tune even with the 19's?

Re: Need ECM guidance
 

Re: Need ECM guidance
 

Right - unfortunately it has been found through a lot of board member experience (including my own) that the 19's will run without tuning, though they act like a 17.5 lb injector, and the offsets are wrong.... like I said they run and the ECM doesn't generally complain, but it's far from optimal. South Bay is good people, but they are not tuners, and though the injectors do flow 19lb on a bench, due to the 1980's programming they don't *run* like the original 19's did. So for purposes of the TPI system you must set it to 17.5 for correct BLM's. Similarly, the 24's (which I currently have) run like a 22.5 injector.

The 19 Bosch III's are good injectors and run really well when properly tuned. But, like all injectors that are not EXACTLY like the originals, there is a LOT more to an injector than it's size - injector voltage offsets, short PW corrections, upper and lower non-linear flow areas.... to name just a few. And all that must be taken into account by the software. If it's not, the results will not be like stock operation.

GD

Re: Need ECM guidance
 

Well there's at least one answer to some of my issues. Under heavy load, the car doesn't feel very smooth and can sometimes backfire if I'm on it hard enough. I got the bosch 19's from Southbay and literally put them in and started driving, no tuning at all as I assumed they would just be plug and play