19 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHNegative fuel trims with 1128/1130 codes
Reported or suspected cause
maf ....(
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that report identifying a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Reported cause
Usually when the "negative" limit is reached the culprit is the MAF ....( but not always)
Leading evidence: 'maf ....(' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'maf ....(' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check maf and/or do a' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed
I just replaced the O2 sensors but that didn't help, though they were due to be changed anyway.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed
I just replaced the O2 sensors but that didn't help, though they were due to be changed anyway.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
I'll take a longer ride tomorrow and check the numbers again.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Unsuccessful attempt
I'm experiencing the same P1128/1130 issue in my MY2000 Tip Cab. I just replaced the O2 sensors but that didn't help, though they were due to be changed anyway.
Run tubing through, squeeze bottle and you have smoke machine
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
If you don't want to spend much on smoke machine, you can make one with 1 liter plastic bottle, clear plastic tubing with ID of a cigarette, one cigarette, drill a hole on the bottle cap for a tight fit of the clear tubing, place tubing thru the cap and into the bottle, light cigarette and install into tubing and then install cap on bottle, a nitrile glove over the throttle body, use small finger cut off tip and run tubing through, squeeze bottle and you have smoke machine.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
19 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
2 acknowledgements have no verified action link; they do not establish a repair result.
Outcome without a verified action link
During quick successive transitions between braking and tipping the acceleration pedal (in heavy traffic conditions or going over multiple successive speed bumps), braking sometimes result in RPM dipping down to 600rpm (usual idle rpm is 680), but restores back to normal idle in the next second after dip.
Hello fellow 996ers, I am in a bit of a pickle and would like to seek some help and advice for my
Year 2000, 996.1 C4 Tip, ROW variant
.
Key Symptoms
Persistent LTFT negative bias (
-3%
to
-8%
on both banks across 5 logged drive cycles), with bank 2 always about -1%~-2% more (negative) than bank 1
P1128 and P1130 will be triggered as pending after a couple of drive cycles, followed by confirmed codes - usually following peak hour heavy traffic city driving start/go, with many traffic idle and frequent accelerate/brake transitions in short succession
During quick successive transitions between braking and tipping the acceleration pedal (in heavy traffic conditions or going over multiple successive speed bumps), braking sometimes result in RPM dipping down to 600rpm (usual idle rpm is 680), but restores back to normal idle in the next second after dip. Single transition from accelerate to brake (e.g. stop for traffic lights) do not cause such dips.
Hot restart (~15min after shutting down engine) sometimes result in rpm dipping down to 550-600rpm on first crank and turnover, but DME kicks in 2-3 seconds later to 'auto-blip' the throttle and brings the idle back to normal and stable at 680-700rpm. (used to stall in the past and requires 2nd crank to be successful, but evap system refresh seems to have fixed this).
Other than the above, all other driving conditions feels normal and responsive. Throttle response also feels normal and responsive during highway pulls.
MAF readings logged (@hot idle ranges from 5.25 g/s to 6.25 g/s, sometimes reaching 7.5 g/s). This sounds high to me, not sure if this is out of expected range?
What I have done (part of old age refresh):
Recently done evap system refresh including purge valve, canister etc. (another issue, but fixed now)
New Fuel Pump and Fuel Pressure Regulator and Fuel Pump Relay
New 02 sensors (02 readings in log shows switching normally, no flatline)
MAF is new, but highly suspicious given readings above. Prior to the new MAF, P1128/1130 was also occasionally present during the use of the older MAF.
Questions/Advice I am seeking:
Is it contradictory/strange to have negative fuel trims (which I think is DME reducing fuel and therefore not a sign of vacuum leak) but yet fault codes P1128/1130 that suggests lean operation? Are the 2 issues related/mutually causal?
I have not touched the injectors at all in my 3 years of ownership. Could it be leaky injectors or broken injector o rings?
Is it possible to have vacuum leaks but yet fuel trims consistently running negative? From a driver's perspective, driving feels normal except for the above symptoms and fault codes.
Can a bad (but new) MAF cause the above?
Anyone has similar experiences or ideas? Thank you in advance!
Mine seems to be at 23-25 kg/h after converting from g/s units. But I am not sure if the MAF is reading/reporting an issue somewhere else, or it is just a case of it being faulty in reporting.
Just sharing this for future references, a complete refresh of the injectors and o rings seemed to have solved the negative fuel trims.
MAF readings seemed to also have normalised after the injector refresh (so the MAF was an innocent reporter rather than a perpetrator).
I'm experiencing the same P1128/1130 issue in my MY2000 Tip Cab. I just replaced the O2 sensors but that didn't help, though they were due to be changed anyway. I'm not sure about the MAF as I got readings of 0.6 to 3.5 lb/hr using an ODBII app.I don't know how that compares to normal values. I haven't tried recording with the Durametric but will do that soon. So far I've read that people have solved the P1128/1130 issue by either replacing the MAF, the cats, or the injectors. I'd like to narrow it down before throwing parts at it.
I finally figured out how to record the values (after only 15 years of having the Durametric)
FRA Bank 1: 1.02
RKAT Bank1: 4.5
FRA Bank2: 1.05
RKAT Bank2: 4.5
Do they seem okay or problematic?
Fault Codes 1128/1130 can indicate rich or lean "limits reached" ..
To determine if the rich limit or lean limit has been reached , you need to look at :::
TRA for 1999 C2 with DME 5.2
RKAT for all DME 7.2 or 7.8
Look for "negative" or " positive" ...limit numbers..
For TRA the limit is +- 3.6ms
For RKAT the limit is +- 6%
@wyovino
is your 4.5% a "negative" or "positive"
Usually when the "negative" limit is reached the culprit is the MAF ....( but not always)
When the "positive" limit is reached, it is usually a vacuum leak ....
I'm also learning about the car, but from my limited understanding, your symmetrical positive RKAT is telling you that you have a lean condition and your DME is adding 4.5% on both banks - meaning you have too much air or you are under-fueling.
I would check MAF and/or do a smoke test. But I am sure others here have more experience than I have to chime in.
I poked around and didn't see anything obvious. Do you need special equipment for a smoke test? I did a reset by disconnecting the battery for abut 30 minutes. After a short drive the numbers look a little better but I don't think it was a good enough drive. Too much traffic. I'll take a longer ride tomorrow and check the numbers again. One odd thing I noticed is that when I have the Durametric plugged in and start logging things at idle, the engine seams to stutter a bit. I'm not sure if it's a coincidence or not but it happened twice.
If you don't want to spend much on smoke machine, you can make one with 1 liter plastic bottle, clear plastic tubing with ID of a cigarette, one cigarette, drill a hole on the bottle cap for a tight fit of the clear tubing, place tubing thru the cap and into the bottle, light cigarette and install into tubing and then install cap on bottle, a nitrile glove over the throttle body, use small finger cut off tip and run tubing through, squeeze bottle and you have smoke machine. also have something to hold throttle body plate open.
might be good to know someone that smokes, have no idea what a pack of smokes cost nowadays
