FiTech 30003 exhaust pop at idle
Hi there,
Been diagnosing a problem along with FiTech support email, but would like more opinions.
Platform:
Small Block Chevy stroked 350->383. Stock compression. Mild 'lopey' cam. Pertronix Flamethrower HEI ignition. FiTech 30003 Injection kit without timing control, single wire from tach signal. No fan control, mechanical fan.
Problem:
Ran well with carburetor, but with extended cold start crank. Replaced Holley 4850 w/ FiTech unit. Starts and idles smoothly and easily. IAC Steps hover around 6, all OK there. Vacuum hovers between -13.8 and -14.9.
Near constant low exhaust popping at idle. Pop is new after having installed FiTech unit. Pop occurs whenever 'AFR' overshoots 'Target AFR' and corrects, even by small margins.
Pop is not heard at engine or carburetor, only behind car or near mufflers. This occurs at operating temperature (170+), as well as during cold warm-up.
Pop does not occur during the first 10-14 seconds of idling during cold-crank/start mode, but begins occurring constantly once idle drops down to normal levels. Vacuum values are normal and do not appear to be stuck.
Solutions / Steps tried:
As suggested by FiTech support :
- Replaced plugs & wires
- Installed additional grounding wire from FiTech mounting tabs directly to negative terminal of battery
- Re-adjusted IAC steps. Within parameters.
- Re-assessed exhaust and hunted down leaks. Small leak found near down pipe from right bank header -- corrected and changed nothing.
- Re-adjusted ignition timing. No matter if advanced, retarded, or near neutral -- constant popping at idle still.
- Defaulted to base V8 map using hand controller
- Reset all learning parameters (repeatedly)
- Capped all vacuum outlets to eliminate possibility of seeing symptoms of an accessory vacuum leak (this popping occurs with or without distributor vacuum advance)
- Checked possibility of bad tach signal -- RPM value is honest and steady.
- Tried different cam settings. 1 seems to act the nicest.
If the 30003 unit allows, I can take a log of the data later this week -- but before I do
- is there anything left for me to check over?
- is there a way to know whether or not I am using an old revision of ECM firmware?
Thanks for all the help.
Just a thought. When I had popping out the exhaust it was due to fouling of plugs. How did your plugs look when you replaced them? When the popping starts, try using timing light to see which cylinder it is and check the condition of that plug. It's either running too lean or too rich, hopefully just too rich.
The previous plugs were ran only for a few seconds with the injection kit -- the car was having them replaced, anyway.
The new plugs, when pulled, appear OK. No overboard smell of fuel or wetness on the plug tip. Pretty normal looking.
I took some log files for FiTech support today, if anyone cares to look them over. Here's the link , since the forum doesn't seem to accept zips.
https://drive.google.com/file/d/1Y5ixZC-6Hlm2SFxsy3AeKlyDB-cmlcc7/view?usp=sharing
Only the most recent logs in the archive are relevant, others were taken either during cold-start or without IAC being adjusted in.
Thanks
FiTech Support got back to me, they say that the logs look fairly normal.
They suggest that it must be an ignition timing problem, or a secondary ignition problem such as cap/coil/wires/plugs etc.
I have ordered a new coil, and will re-set ignition timing using a light to a known good point.
Will update the forum if I make any progress.
Any wisdom is appreciated.
Thanks
Simple mechanics, if it's not firing on the plugs consistently it will pop through the exhaust. It's either too much fuel, not enough fuel, or ignition problem. Hope you narrow it down.
Simple mechanics, if it's not firing on the plugs consistently it will pop through the exhaust.
Absolutely, I agree -- what has me dumbfounded is why switching from a carburetor to a fuel injection kit created a pop that I'm chasing by changing ignition components.
The only thing that has changed is the injection kit -- and the car ran fine before the install with a carburetor.
Nothing changed, ignition wise -- My only guess would be that the carburetor AFRs were so out-of-tune that the fuel simply wasn't present to create a pop in the exhaust system regardless of the true culprit that may be present in the ignition/timing?
We've tried a new HEI coil. plugs, wires, and toying with the ignition advance adjustment available by twisting the distributor. No notable changes.
My next step is to re-time the engine from TDC with a new distributor -- I didn't install the present distributor myself, so i'm relying on the previous install having been done right; would rather re-do it myself and witness how it goes.
Will update this post with any news.
Thanks.
Hi there,
New update and good news.
Pulled distributor cap on the way to retime it and rotor had broken into a few pieces.
Replaced the rotor -- still typical pop.
Removed distributor and re-timed by physically checking valve closure without valve-covers; timing was off a few teeth.
re-timed to #1 TDC. Still tuning for maximum vacuum, but seems to run without pops.
Amazed that the car run at all with the rotor in pieces when the carb was installed -- I imagine the dead cylinders were intermittent and random, so the owner of the car didn't seem to notice the performance problem.
Thanks for all the input -- the help is really appreciated.
Simple mechanics, even if they boggle the mind sometimes.