Just replaced a carbon fouled NB O2 that I thought was causing fueling issues. (383 Xfire, EBL, 80# TBI Injectors...) It appears to be giving me correct readings. Still having issues though..

1. Rich at idle (op temp) ... AFR in high 12's
2. Rich on cruise/ 0%TPS...high 11's
3. Smelling what I believe is un-burnt gas with sustained 50%+ throttle under load

Progressively learned leaned VE tables do not improve running condition.

Some questions -

I pulled the EGR. Are there EBL bin Scalers I need to fix?

Will bad IAC's impact performance/AFR readings at 50%+ throttle and 0% throttle cruising?

Can IAC count readings ID bad IACs? What do I look for?

Plugs could be fouled by carbon... assume bad plugs can cause poor AFR readings??? Un-burnt gas odor?

Vacuum leak? I did test a while ago... Good thread for vacuum leak test?

Jump in with suggestions... Thanks.

 

Nothing jumping out? Well, back to basics... plug, fuel pump, wires, modules, vacuum leaks, distributor... ?? most parts under 3k miles. Thinking vacuum issue or fuel pressure... What else would cause rich running with poor results when VE's are reduced? Will post if solved...

 

OK guys, need some input here. Anyone who has done the cigar smoke test looking for engine vacuum leaks... Plugged IAC and TBI ports and blew as much smoke as I could into the primary manifold vacuum port... the only smoke leaks I could find where at the two TBI throttle butterflies shafts... BUT ... it was minimal.. AND... I could not feel any play in the shafts.

Thinking shafts can not be air tight and these TBIs were rebuilt by Dynamic CFI (Renegade folks) less than 3000 miles ago. So I shouldn't worry about that - right or wrong?

Um, Swisher Sweets, yep I'm ready to barf. ��

 

Follow up - Well kids, I'm feeling some pulsating air although a slight amount when I put my hand near the exhaust at the block. Both sides... reading this could play havoc with your tune. Could this be my problem? Rich running, crap acceleration, louder than normal engine... Wondering if the last shop I had this at knows I have a FOID.... Anyway, continuing on this. Will post results.

 

What are the fuel trims doing?

Get enough air into the exhaust and the O2 sensor will react to it.

RBob.

 

At idle (875 RPMs) in open loop INT & BMT read 128 & AFR reads 11.4, about 15 seconds into closed loop INT/BLM drop to 109/108 where AFR reads ~stoich. A second or so later I'm getting 127/118 readings with AFRs in the low 12's --- that an indication of too much air?

Observed - trims at idle struggle to lean things out but 11's and 12's pop back in and for the most part it runs rich. Can smell it too.

At light cruise INT/BLM 121/108 with near stoich AFRs.

With 30-50% TPS and some load is where it runs erratically, INT reads ~115 (when AE kicks in) ~123 if no AE, the BLM tends to reads ~108 regardless of AE and AFR's are all over the map ranging from 12's to as a single line read 19.4.

 

OK, fuel trims dropping like a rock. Which means that the ECM is pulling fuel out due to feedback from the O2 sensor.

Did you set up the BPC - BPC vs VAC table for the engine displacement and injector flow? What fuel pressure are you running?

RBob.

 

Thanks. I did the set the BPC. FP is at 24 Lbs (VRVFPR). So something looks wrong... Could it be VE tables are still too rich and more learns are required? I could reduce the VE tables by a factor. I have not tried this with the new NB sensor in yet. Was getting corrections of 10 (%?) across the board 1st two learns. Also , could the SA table have an influence on this? Thinking my plugs could be carbon fouled based on what the old NB O2 looked like - I'll evaluate "em - could be contributing to why it misses under load.

BTW - it doesn't look like an air leak is messing with the O2's , does it?

 

Double check the BPC vs VAC table. It should be 84 at 0 KPa and 116 at 80 KPa.

As for the manifold leaks, at this time it doesn't appear to be affecting the O2 sensor.

RBob.

 

Thanks, just back from a short trip... Yes, those two points agree with above.

 

Could be my tuning issue....

Plug eval shows driver bank running rich (carbon) much richer than the other bank. TBI patterns look Ok, running parallel plumbing, VRFPR, 80# flow matched injectors..

Bad IACs? Other causes??

Pic #2 and #1 plugs, respectively. Other opposite bank plugs compare similarly.

 

I believe the TBI that fuels the driver bank has a wider "in" line than the other TBI. Could that be the issue causing unbalanced fueling? Pressure should be the same - no?

 

Folks on FB are telling me I need to use the 3001 offset since I'm running 80# injectors... looking at that. Will post...

 

Put the iridium plugs on the shelf and get some plain orange box copper core AutoLite #24 plugs. I usually gap them at .035"

See what kind of difference it makes.

RBob.

 

Thanks - next fix... It is running better... BTW I was looking for direction on that but in the meantime cleaned the old one's up and tossed "em back in. They seem to be running OK>

 

Well, well, well.... Captured the injector correction deltas, replaced the injectors with an older set of 80's I had and it has never run better... AND... when I capture a learned bin it runs even better... AND... it's not missing under load.... AND... it is one quick car!!!! BTW thanks for all the help guys. Especially RBob and the guys at FB CFI Modified for the tweaked Bins that set me on the right track! Still has a way to go but I never felt more positive about being on the right track.

 

So just a concluding comment - I believe defective injectors were causing all my problems.Running imbalanced and so rich my sensors and plugs were fouling. I'm sure the fueling corrections helped some but the values were not that far off. Made the mistake of purchasing these bad injectors on ebay. Seller had excellent ratings and claimed they were flow matched. Noticed there were no part number markings on them so who knows what they really were. If you buy injectors get them from a trusted recommended source (that could be an ebay seller but get references) and pay the premium price - well worth the potential frustration it will save you.

 

Good advice. Thanks for reporting back on the final solution to the issue.


Did you ever switch to the plugs Rbob recommended? I know when I worked in a Chevy dealer in the '80s, I was a huge Bosch Platinum fan. They cured a specific condition on a non-GM vehicle I owned. But our top techs, while they appreciated that fix for that car, said for GM vehicles, to stick with a stock style copper core plug, with preference for AC. They had just had the best luck with them, having cured many "mystery" misfires by pulling Champions, etc., and installing ACs.

 

Not yet but I plan to. Will post results... Thanks for advice.

 

Plugs ... Need a set of shorties due to header clearance. Not finding any AutoLites. Some folks recommend NGK UR5's as an alt - Any Comments? Also, 383 build shop put in .460" reach plugs, someone recommended plugs with a 3/4" reach. There a way I can determine if 3/4" reach will work?

 

What heads are on the engine? That will determine which plugs to use.

RBob.

 

Must confess, the only two things I know about "em are aluminum and 64 CC chambers. Bit off topic but my digital dash instant and average mileage are frozen at 0 and 12.8 yet your EBL displays these values correctly . Is that an indication the ECM serial output should be OK or is the EBL calculation independent of the ECM?

 

Most aluminum heads use a 3/4" reach spark plug. Which are going to be a bear getting them installed. The threads will be filled with carbon.

But you really should try to find out which heads they are first. Check the front face of a head. If nothing there then pull a valve cover. They should be marked by either a machined in or cast in identifier.

As for the digital dash, that is updated via the ALDL link. Make sure this flag is set:

Option Word 3 - Bit 7 - DglDh

RBob.

 

Carbon on the threads - dang you're right. Maybe not too bad engine has probably < 4k miles on it. I measured the depth (mating surface to inside wall of head) it is 3/4", so I assume there will not be piston interference if I go to a plug with a 3/4" reach. Still need shorties for clearance in two areas. Thanks for ECM info...

 

It's already "set" as DglDh... Anything else I can look at?

 

If a HAM board is installed check that strap JP3 is jumped between 1 & 2.

If a re-terminal and newer connectors are installed, check that position A8 (ORN?) is OK.

RBob.

 

HAM board not jumped. Assume that will do the trick. Much appreciated...

 

Well, too optimistic... Instant not working (stuck at 0) but the reset appears to be doing something with the average mileage - I now get one of three numbers when I hit the reset 99, 25.6, 12.8... Ha! Not something I can't live with... Reading issues with this display are not uncommon.

 

There is a BIN parameter for the injector flow rate, can use it to calibrate the dash:

DGD - Injector Flow Scalar

RBob.

 

I'm not getting an instant MPG so I'm thinking there is a signal reading issue/possible short somewhere. The average MPG doesn't seem to calculate either (after half hour+ driving) it just displays one of three numbers 99, 25.6 or 12.8 depending on it's mood. I'm closing up the dash and ECM - gave up and am concentrating on the tune. Thanks for your input...

 

Follow-up - I opted to buy NGK equivalents of the Autolite 24's (NGK R5724-8/7317 - Summit $2 a pop) . NGK is a shorter plug and I have header clearance issues. These are copper cores with identical reach and heat range. I gapped "em at .035. Also, very carefully checked head depth including a visual with an endoscope. This cuz my old plugs had a .46 reach and I was very concerned about mechanical interference. OK to the punch line - Took it out for a couple of short spins - Significant improvement in acceleration and idle. Definitely on the the right path.... back to some serious tuning soon. Thanks for your recommendations, folks.

 

So many little variables. I'm glad those worked for you.

 

Thanks, back to the tune and I'm getting confusing results. VE's lean mix and when captured it knocks. Playing with SA and i can eliminate knocks by reducing SA but it runs poorer. Something is still not right...

 

Appeared to be on the right tuning path but it looks like I still have some issues to resolve. In a nut shell - VE learns are leaning the mix but when I capture the learned bin I get knocks. Seems I can eliminate knocking by reducing SA but it runs poorer. Below is an analysis snapshot - note at WOT it's leaning itself/starving for fuel. Need to find the cause. AFRs are way too lean for WOT should be reading in 12's. Right?
Comments on what I should start to trouble shoot welcomed.

 

Frustrating but after reading up more it sounds like I should move to WB learns once NB learns result in a civil ride. Believe I'm past that. So it's on to WB open loop learns... will post...

 

Went to WB Open Loop Learns - leaning like crazy but even as I'm using the original SA table I'm no longer getting knocks. Appears I'm back on the right path. NB BLMs were really working against me - not sure why but for those who might be following this thread someone should explain where and why you jump off NB BLMs. EDIT - Wrong it's still leaning things out. I'm confused. It is running better but knocks are coming back - not as many as before though. Someday I'll figure this schtick out.... Maybe the fuel pump can't hold up under heavy throttle.