Mark_ZZ3

Odd thing ... looking for some ideas.

Engine started to have a rougher idle. Decided to check it out with Tunerpro and discovered my BLM was at 160!!!

Now this is an older setup I haven't done much with in years. Back in the day I put in 24lb injectors and adjusted the fuel pressure to get the BLM's closer to 120.

Given nothing has changed with the engine in years ... what would make the engine go lean?

- I checked the plugs and for sure it's lean.
- I checked fuel pressure and it was 37 at idle and 45 with vac removed on regulator.
- I checked for obvious vac leaks ... found one plug was missing on the port at the bottom of the TB on the driver's side. I plugged it.
- nothing else is odd.

Tunerpro still shows 158-160 BLM.

Am I looking at a bad MAF? Vac leak?

Any ideas welcome.

Mark.

Mark_ZZ3

Sharing data ...

Did some troubleshooting.

- Check for Vac leaks. nothing major but tightened up what I could. At worst case ... slight vac leak. No big holes.
- Ran a test without the MAF ... seemed to run better. Noticed the MAF air value is higher than what my MAF reads at idle (uses a table I assume). In that case ,it would add fuel to the idle which is what it does with the MAF connected.
- verified MAF burn off works. Tested without the air cleaner on.

Here is what I discovered as possible cause. My battery voltage was sitting at 11.xx with the key on, door open, waiting to start. I start the car and watch the data ... O2 starts richs, drops fast to lean. Then the INT and BLM go up up to 150-160. During this time my voltage is still under 12 volts.

My Alt won't charge until your rev it up a bit to create the difference needed to excite the Alt. I must have missed that wire when I did the V8 swap.

In another test, I started it, reved it up quickly to get the battery in the 12.xx range at idle. And the INT and BLM settled in the 130's.

So my issue is voltage. Alt doesn't kick in right away and may not be providing enough charge at idle.

Weird. Would not have guessed.

Next steps ... check wiring for culprits. Also to look into PROM and adjust the fuel for lower voltage.

Battery is on the charger at the moment ... seemed to run it out. it would crank by not fire. Which suggest I need to check the wiring at the distribution block and coil. It should spark if it can crank.

Mark.

Mark_ZZ3

Quick update.

The sense wire on the Alternator showed the same voltage at at the battery. I rewired the sense wire to be along the main power wire that goes into the IGN. Now I see a 0.02v drop. I only had time for one start ... the alternator did not start charging right away as I hoped, but a quick rev saw the alternator charging HIGHER than ever. The only change is the sense wire.

I've struggled for years on this vehicle with alternator charging issues ... turns out it was most likely a mistake on my part with the wiring.

Need to get out for some test runs and see if the lean condition is gone.

Mark.

Reid Fleming

iTrader: (2)

I went through 2 batteries and 2 alternators within 2 years of each other. Once I went with the battery and alternator cable kit from Innovative Wiring, it's been smooth sailing ever since. Their kits are nicely built with oversized everything.

Mark_ZZ3

Well ... crap.

After additional testing ... my setup ran lean again.

The data suggest I am seeing a MAF reading of 6.80 or so at 600rpm idle. That is too low in my opinion. My son's 305TPI sees 7.4 or more. I think my MAF is lazy somehow OR was always out of calibration. I could not find any leaks in the air flow.

I'll have to swap MAF and see if the numbers change. Or worst case ... I'll adjust the MAF table at idle to bring it back into spec (so to speak).

Mark.

Mark_ZZ3

Well I am stumped.

Engine barely started today. When I did get it running, the data stream started out at .900mv for the O2 ... quickly goes down to 0.100 and lower. BLMs go up to 160. Engine stumbles. At one point BLM is at 160 and INT is 150 and the O2 starts bouncing up and down again.

- No error codes.
- TPS at 0.53 at idle.
- battery charging at 14.5-14.7. (It was 13.5 before ... fixed that).
- Tried a different MAF. Same results. Tried with it unplugged ... similar results, but still tries to adds fuel.
- Tried no o2. ran bad.
- Fuel pressure when engine running is 42.5 (vac connected). I had upped this a bit to see if that made a difference. nope. Fuel pressure is stable during idle. No change in idle when I disconnect vac from regulator. Still lean.

Best I can figure ... there isn't enough fuel for the amount of air drawn in. MAF seems ok. So maybe an air leak. I checked all the usual culprits. Nothing. I have no EGR (Edelbrock heads have no crossover). I checked all the bolts. Air intake tubes.

Feels like the fuel pump or fuel filter.
Or maybe my injectors all got dirty from a bad fuel fill up? (I filled up the tank the day before).

Looking for some suggestions. This just showed up. No changes to the engine or engine bay in years!

Thanks for letting me think outloud.

Mark.

Reid Fleming

iTrader: (2)

Do you have a vacuum gauge? If so, what reading are you getting?

How old are the injectors? How long since you cleaned them? How many miles on the car? How many ohms are the injectors reading?

I don't think it's a fuel pump. You'd be seeing low pressure.

Mark_ZZ3

Yes I have a vac guage ... will check readings this evening.

Injectors are 10-12 years old or so. Have not cleaned them.

Ohms are 15.6 for all.

I may have put 5000 miles are the engine in the last 10 years. Mainly shows and cruises.

Mark.

Mark_ZZ3

Dumb question ... Tank of Bad Gas???

I recently filled up. Drove for a day. Thought idle was rougher than usual. That's when I started scanning the data.

The gas I drained out of the fuel pressure gauge when testing wasn't as "smelly" as it usually is. typically the garage smells like gas for a day or two. This time ... it's ok.

I'll have to pick up some basic additive and maybe top up the tank from a different company.

Mark.

Mark_ZZ3

More testing today. Some success.

Connected Vac gauage. Was around 15 at idle. Maybe 14 when warming up and 15.5 when warm. No real jumps. I am running a ZZ3 cam.

During the first test it ran like crap crap. Vac was at 5 and barely running. I noticed the PCV hose was out. I must of dislodged it when I measured the O2. So put that back and it idled better. Engine was still lean, BLM's in the 140's. Better than yesterday. (maybe PCV was part of that issue).

I noticed a slight exhaust sound. The driver's side pipe was loose! Tighten that up and it seemed to run better. BLM's lower, but still lean.

So now ... I tweaked the MAF 1 table and made the idle values larger so the it would add more fuel. I got the BLM and INT to sit around 128!!! Plus or minus 2.

When for a run ... seemed good. Did a WOT test ... O2 was in the 900 range for the duration. Felt strong. spark was good. No retard.


Sooooooo ... what I have learned.

- Bat volt was an long standing issue. Made for a poor idle.
- PROM was too lean at idle. This was a 1987 stock PROM with a modified engine.
- Driver's exhaust was loose. May have caused an incorrect o2 reading.
- Vac leaks ... nothing major anywhere, but may have been some slight ones.

I think I may have created more issues as I tried to solve them ... but they would have shown up at some point.

I hope some of this triage helps someone else down the road.

Cheers!
Mark.

Fast355

iTrader: (2)

With lower than expected MAF values I would still be looking for a vacuum or meter air leak. Don't overlook the intake boot between the throttle body and MAF and the PCV vent piping. Also something as simple as a missing seal on the oil cap can cause a metered air leak and lean running. I would use carb cleaner to hit the vairous o-rings and gaskets that seal the intake. I have seen fuel injector o-rings cause vacuum leaks more than once.

Reid Fleming

iTrader: (2)

You beat me to it. I was just going to say that high BLM at idle with no vac leaks would suggest an exhaust leak.

Getting the INT and BLM to settle around 128 sure does feel good. Engine just purrs when you do that.

Mark_ZZ3

My radar is super sensitive now ... so it still feels like it isn't idling as smooth as it should. I got side tracked on another project, so I will have to get back to my ride shortly.

But yes ... when it's neat 128, it does seem smooth!

Mark.

89FormulaDan

I know this is an old thread but...
maybe since you said the gas didn't smell as bad/strong as usual...
could the last fill up been contaminated with E85?
If bad gas is suspected you have to drain the tank and fill with fuel from another reputable gas station.
Contamination could have been through an error at station or at fuel depot, but E85 is cheaper that real gas so maybe someone is trying to increase profits!

Mark_ZZ3

I've swapped the intake setup on this engine over the winter to a Superam with 36lb injectors. Now tuning with a wideband O2.

Found out my MAF was acting up. Had one value at one startup, and something different on another. Swapped in a spare ... and it is now consistent.

Now on to more tuning. Wideband is a new tool.

Mark.

89FormulaDan

Hey Mark,
Didn't really expect a response! Just wanted to put another possibility out there. Glad you found it, so the MAF "lies" to the computer so it under-fuels causing the lean readings at O2 sensor and poor running issues. Yeah, a flaky sensor is hard to pinpoint. Did you ever here the one about tapping the MAF while the motor is running... if it's good no change in idle, but a bad one would cause fluctuations?

I once lucked out in buying a car that wasn't running right. No noises from the engine but idle was up and down and when you put it in drive it would stall unless you feathered the pedal. Made a deal with seller but had to come back with a driver to get it home. Returned next day, paid him, and he says 'hope you make it home'! I was going to wait until I left his place but...
I took out a spare MAF I had and quickly swapped it out. Started the car and it ran perfect. You should have seen the look on his face!

The SR is a nice intake, but with a 350 all you need is 30 lb injectors. If the capacity is not needed I think the possible loss in atomization of the fuel is a detriment. Now a 383 or 406 is another story!