LT1 datafile experts...help needed

[Bartman]

So my car runs pretty good most of the time, but it stumbles sometimes at low RPM's. If you give it a little more gas it eventually get's beyond the probem, and takes off. I've been trying to find vacuum leaks, and I found one and fixed it (still have the problem). I checked all my plugs and regapped them and they all seem fine, so I finally made a recording with DataMaster to see if something shows up. I put the file on PutFile at http://putstuff.putfile.com/82934/6587804

I haven't researched it too much yet, but I have a couple of error codes even though my SES light is not on, MALF 16 - Lo-res fail and MALF 33 - MAP high. My fuel Trim cells are varying a lot and the EGR DC fluctuates sometimes and the CCP DC fluctuates a lot. I don't have an EGR and I don't have a charcoal canister on my install, so maybe these aren't turned off on my computer and they should be.

 

Any help would be appreciated, I will be doing some research as well.

[Bartman]

So after some investigation I've discovered a couple of items of interest. First, the MAP KPa is captured in my datafile and it is a little high; but that may be because of my cam and therefore a non-issue (if this is true, then I can just ignore the 33 error). The 16 error code is still a potential problem that has to do with the Opti not providing the the PCM with the low resolution pulse it expects to be seeing (I just replaced the Opti not to long ago). I will double check my Opti wiring to see if that is the culprit for this issue.

 

The most interesting thing I've found is that when the problem is occuring the left short term counts are low and the right short term counts are high. The O2 sensors are fairly new as well, so I don't know what could be causing this problem. I don't think they are reversed, but I will double check that as well.

[wheelman]

It could be that the low res signal problem throws the injector timing off and one side gets more fuel injected than it should. I'd get the low res problem fixed before doing anything about the counts. It sounds to me like you may have an intermittent connection problem in the opti wiring, especially since you already replaced it once. I remember Tim saying something about a weird stumble he attributed to the opti so maybe the wiring issue has been there right fromt he start.

 

BTW: Not to change the subject but were you able to attend that Auto-X practice session you mentioned?

 

Wheelman

[Bartman]

It could be that the low res signal problem throws the injector timing off and one side gets more fuel injected than it should. I'd get the low res problem fixed before doing anything about the counts. It sounds to me like you may have an intermittent connection problem in the opti wiring, especially since you already replaced it once. I remember Tim saying something about a weird stumble he attributed to the opti so maybe the wiring issue has been there right fromt he start.

 

BTW: Not to change the subject but were you able to attend that Auto-X practice session you mentioned?

 

Wheelman

I will definitely check my wiring tonight.

 

The Auto-X practice session I wanted to attend was full, but I'm signed up for a different one this Sunday. I'd like to figure out this problem first, but I'm going even if the problem isn't resolved.

[wheelman]

Let us know what you eventually find.

 

I'm sure you'll enjoy the practice session even if you have a little bit of a stumble.

 

This last weekend our club did the annual driver's school.

It was split into 2 sessions with a different instructor in each. The morning instructor I was with really didn't help me much, he races front wheel drive cars and didn't drive mine but the afternoon guy was a big help. I drove the first of 5 runs, he drove the second then I did the remaining 3. He scared the $hit out of me, in a good way. I thought I was pushing the car but found just the opposite. I have a much better picture of just what the car will do now and was able to shave 2 seconds off my already pretty fast times. By the end of the day I had the fastest clean time of all the students. The instructor said he wouldn't change a thing about the car other than to install power steering and said he was very impressed.

 

Unfortunately I now have a thumping sound coming from somewhere. I'm not sure what's causing it yet. I've checked the wheel bearings, CV joints, brakes and don't think it's a diff bearing. I'm beginning to think it's just flat spotted tires (both the instuctor and I locked the brakes several times). I'm going to pull my good rims and run the old Enkies to see if the thump goes away. The tires on the Enkies only have 50 miles on them and I've kept them stored laying down so they should be fine.

 

Because of the thump I decided not to run it on Sunday and Monday. I co-drove my Mustang with my daughter on Sunday and a friend's first gen MR2 on Monday. I found out just how much work the Z is to drive. I normally come home from an event totally beat but was barely tired from driving the Mustang and the MR2.

 

Wheelman

[80LS1T]

Well it seems to me that code 33 could be from your cam. Code 16 sounds like its a wiring issue though(hopefully)....

 

CIRCUIT DESCRIPTION

The distributor ignition system supplies two timing inputs to the Powertrain Control Module (PCM) , a high resolution signal (180 pulses per one crankshaft revolution) and a low resolution signal (4 pulses per one crankshaft revolution). The PCM can determine if one of the timing inputs is not being received by comparing the two inputs. If the PCM detects the high resolution timing pulse without detecting the low resolution timing pulse, this Diagnostic Trouble Code (DTC) will set.

 

The reference signals toggle between 0 and 5 volts as the camshaft turns. Therefore, an open, a short to voltage, a short to ground, or a defective sensor inside the distributor can prevent the voltage from pulsing at the PCM.

 

DTC 16 WILL SET WHEN

The PCM detects 720 high resolution timing pulses before any low resolution pulses are detected.

 

ACTION TAKEN (PCM WILL DEFAULT TO)

DTC 16 will be stored in the PCM memory, but will not turn "ON" the Malfunction Indicator Lamp (MIL) . Fuel pump and injector operation will be disabled.

 

DTC CHART TEST DESCRIPTION

Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the engine starts at this point, DTC 16 is intermittent.
   
2. This test will determine if the PCM is sending out a signal to the distributor for processing. If this signal is not available or is shorted to ground or voltage, the distributor cannot ground it to produce reference pulses.
   
3. If a DTC 41 and/or 42 is also set with a DTC 16, and no external fault can be found, replace the PCM. If only DTC 16 is set and distributor connections are OK, replace the distributor.

DIAGNOSTIC AIDS

DTC 16 will set if the high and low resolution signal circuits are shorted to each other. Before replacing any components, make sure these circuits are not shorted together. If DTC 16 does not reset and the vehicle still does not start, refer to Diagnostic Charts/A Charts/Chart A-3.

 

NOTE: When equipped with Opti-Spark distributor, if components must be replaced, check distributor vent system. Refer to Diagnostic Charts/C Charts/Chart C-4C.

 

When an intermittent DTC 16 occurs, a misfire may be apparent. To locate an intermittent, use the Tech 1 scanner's Snapshot feature and try to duplicate the conditions under which the misfire is present. When reviewing the captured data, watch for any abnormal high and low resolution timing pulses. Refer to Diagnosis by Symptom/Cuts Out and Misses. See: Symptom Related Diagnostic ProceduresCuts Out/Misses

 

 

 

Hopefully you don't have a faulty PCM or a bad NEW opti....

 

Guy

[Bartman]

Let us know what you eventually find.

 

I'm sure you'll enjoy the practice session even if you have a little bit of a stumble.

 

This last weekend our club did the annual driver's school.

It was split into 2 sessions with a different instructor in each. The morning instructor I was with really didn't help me much, he races front wheel drive cars and didn't drive mine but the afternoon guy was a big help. I drove the first of 5 runs, he drove the second then I did the remaining 3. He scared the $hit out of me, in a good way. I thought I was pushing the car but found just the opposite. I have a much better picture of just what the car will do now and was able to shave 2 seconds off my already pretty fast times. By the end of the day I had the fastest clean time of all the students. The instructor said he wouldn't change a thing about the car other than to install power steering and said he was very impressed.

 

Unfortunately I now have a thumping sound coming from somewhere. I'm not sure what's causing it yet. I've checked the wheel bearings, CV joints, brakes and don't think it's a diff bearing. I'm beginning to think it's just flat spotted tires (both the instuctor and I locked the brakes several times). I'm going to pull my good rims and run the old Enkies to see if the thump goes away. The tires on the Enkies only have 50 miles on them and I've kept them stored laying down so they should be fine.

 

Because of the thump I decided not to run it on Sunday and Monday. I co-drove my Mustang with my daughter on Sunday and a friend's first gen MR2 on Monday. I found out just how much work the Z is to drive. I normally come home from an event totally beat but was barely tired from driving the Mustang and the MR2.

 

Wheelman

Sounds like the driver's school is a good event to attend. A friend of mine had the flat spotted tire problem and it sounds exactly how you describe. Hope it something that simple and not a bigger problem.

Well it seems to me that code 33 could be from your cam. Code 16 sounds like its a wiring issue though(hopefully)....

 

Hopefully you don't have a faulty PCM or a bad NEW opti....

 

Guy

Guy, thanks for posting all the information. I have the FSM and should be able to find it all myself, but I guess I haven't figured out how to use it properly.

 

According to the info you posted, my problem must be intermittent because the engine starts. I'll try and run some more tests tonight.

[Bartman]

So I was able to find all the information like guy posted in my FSM. I went through all the tests and couldn't find any problems, so I went ahead and put everything back together and made another DataMaster recording. The 16 error went away and the 33 error code changed to a 34! I tried it a couple of times to make sure and the 16 never came back, but I always got the 34. Maybe a bad connection where I neeed to disconnect to run the tests.

 

I'm thinking of replacing the MAP Sensor to see if that takes care of the 34 error. The FSM talks about comparing values to those of another car and using a vacuum pump, so it just seems easier to replace it.

 

Regardless, I still have the stumbling problem. I can pretty much make it happen at will by giving it a small amount of throttle when the engine is running at low RPMs, so maybe this is a load related issue. I just checked my plugs and gaps last week and everything seems to be fine (I gapped them at .045). Maybe I have a problem with my ignition wires. I'm running them underneath to make for a cleaner look, and maybe that's causing a problem somewhere. My O2 sensors are quite a way down my exhaust, maybe that could be a problem as well.

 

I'm not sure what the problem is at this point, so any suggestions would be appreciated.

 

When the problem is occuring it actually goes into open loop for very small intervals, the BPW mS jumps around and the short term counts for the left and right side are completely out of whack...the right side goes up while the left side goes down. The problem area is between 335 and 399 seconds in the DataMaster file and it goes into open loop at least four times during this interval.

[80LS1T]

Well the MAP sensor is kind of like a load sensor for the PCM, so this could cause some serious drivablity issues if its going bad.

 

CIRCUIT DESCRIPTION

The Manifold Absolute Pressure(MAP) sensor responds to changes in manifold pressure (vacuum). The Powertrain Control Module (PCM) receives this information as a signal voltage that will vary from about 1.0 - 1.5 volts at idle to 4.0 - 4.8 volts at Wide Open Throttle (WOT).

 

The scan tool displays manifold pressure in kPa of pressure and voltage Low pressure (high vacuum) indicates a low voltage while a high pressure (low vacuum) indicates a high voltage.

 

DIAGNOSTIC TROUBLE CODE (DTC) 34 WILL SET WHEN

MAP is less than 16 kPa, and RPM is less than 700 RPM, DTC 21 not set or MAP less than 16 kPa, RPM greater than 700 RPM, TP sensor angle greater than 26% and DTC 21 not set and all conditions met for 1 second.

 

ACTION TAKEN (PCM WILL DEFAULT TO)

If the MAP sensor fails, the PCM will calculate a MAP value based on throttle position and engine speed (RPM). The Malfunction Indicator Lamp (MIL) will illuminate.

 

CHART TEST DESCRIPTION

Number(s) below refer to circled number(s) on the diagnostic chart.

 

1. If the PCM recognizes the high MAP signal, the PCM and wiring are OK.
   
2. The Tech 1 scanner will not display 12 volts. The important thing is that the PCM recognizes the voltage as more than 4 volts, indicating that the PCM and CKT 432 are OK.
   
3. An intermittent open in CKT 432 or CKT 416 will result in a DTC 34.

 

 

Another thing to do is a voltage drop test your your ground wire on the MAP sensor. While its plugged in and engine running, take your voltmeter on DC voltage and connect one lead to the negative battery and then back probe the ground wire on the MAP sensor connector. If you have anything more than .2V then you have a poor ground and this can cause bad signals back to the PCM. This test works much better than ohming the wire because its like a load test on the wire and not just testing continuity.

 

Guy

[bodie]

what are you long term fuel trim?

is that the cam you have in you sig?

are you still runnig stock programming?

both code could be none issue and you have another prob

 

if you have one

try running you can with out the maf plugged in

[78zlt1]

Found this on the LT1 Fiero site http://www.fierolt1.com/faq.htm, Have no idea if its what you are experiencing just thought I'd throw it out here.

 

 

 

Why does my car have a slight stumble upon slow acceleration?

 

If it usually occurs from idle when then engine is warm and you get a short backfiring just before shifts, then it's probably the coil wire or the coil itself. If you notice the headlights flicker or flash at night when the car stumbles, it's almost assured the coil and/or coil wire need replacement.

[Bartman]

My problem only occurs after the car is warmed up and in closed loop. It happens at low RPM's when you give it a small amount of gas. If you hit the gas hard enough, there isn't any problem. I just ran it at an Autocross event yesterday without any problems (since I'm constantly on the throttle fairly hard). The most confusing thing to me is the difference between the left bank and the right bank in my data recordings.

 

I still need to check and resolve the MAP Sensor errors, 33 previously and now 34.

 

The data in my signature is current.

[bodie]

only in closed loop, you may possible have a bad o2

check long term fuel trim and see which is furter off of center

unplug o2, reset fuel trim and drive to see if it fix it temporality.

[Bartman]

only in closed loop, you may possible have a bad o2

check long term fuel trim and see which is furter off of center

unplug o2, reset fuel trim and drive to see if it fix it temporality.

The long term counts are off when the problem occurs, but not as far off as the short term counts. I just replaced the O2 sensors, but they are quite a distance down stream. Since their heated it shouldn't be a problem, but I still wonder if I should move them closer to the header.

 

If I unplug the O2s, how do I reset the fuel trim? Then I can make a test run with them disconnected?

[bodie]

the long term is what you have to worry about, short term go off the long term adjust to try to bring short term back to center

you can run with the o2 unplugged it will stay in open loop, and wont adjust for that side

unpluged one at a time and observie 02 and trim readings

 

depeing on year of you pcm you can either unpluged the battery for 30 min , disconnected the ecm fuse for 10 min or use a tech 2

 

as long a your 02 are not at the rear wheels and are between the 9 12 to 3 o clock position you shouldnt have a problem.

[Bartman]

I'm still experiencing this problem, and it's really got me frustrated. I replaced the MAP Sensor and the ignition wires as well as rerouted the ignition wires to eliminate potential problems with the headers, all to no avial. I need to generate another DataMaster file to see if I still have any codes being set (the MIL light is not on).

 

It still seems strange to me that this is only a problem after the engine is warmed up and in closed loop. To some extent the problem is worse at some times than others, and I thought for a while that it was solved when I replaced the ignition wires.

 

A couple of items:

I noticed last night that the alternator light would flash every once in a while, so I don't know what can cause that and if that can be a factor as well.

 

It runs without the maf plugged in...but not very well.

 

I saw the item 78zlt1 posted from the LT1 Fiero web site, but my car doesn't backfire before shifts.

 

I do get the sense that it is an electrical problem, as it seems to be worse when I'm running my AC...of course, that adds load as well.

[80LS1T]

Did you ever figure out if you actually have the EGR and canister are turned off in you PCM?

 

I just downloaed Datamaster and I was looking at your file, it seems to me that you PCM thinks the charcoal canister is purging but its really not and your short term fuel trim is going rich causing it to stumble?

 

It's been quite a while since I used Tunercat so I don't remember how to turn that stuff off. I just remember how to turn off the codes, which I don't believe is the same as turning off the function of the EGR and CC. I think you have to make the parameters that it needs to turn on so far off the chart that it will never see them that it will never turn on. Is that what you did?

 

 

Oh and how do you have your O2's mounted? They should not be mounted in anything lower than the "9 oclock to 3 o'clock range because water could rest on them and burn them out when they initially heat up when first started.

 

Guy

[Bartman]

So I made another recording last night, and I don't have any codes whatsoever...but I still have the problem. It seems to not be as severe, but it's there nonetheless.

 

The EGR and canister values are still jumping around, so I need to figure out how to turn that off if possible, but I don't know if this can have anything to do with my problem.

 

When I have the problem I'm still seeing one bank going lean while the other goes rich. This seems to be the key, but I haven't figured out why and what I can do about it.

 

Guy,

Thanks for looking at the datafile for me, I think we're both seeing the same thing. The O2 sensors are mounted horizontally, one at 3:00 and one at 9:00.

[80LS1T]

Upload the new file tonight if you can. I'll take a look at it when I get home tonight.

 

I would make sure you have all the emissions stuff off that your not using and then clear all the codes and unplug the battery to reset the PCM. Then take it for a ride and see if it still happens. If the PCM thinks it's purging the canister or EGR I could easily see it richening or leaning out the mixture to compensate for the extra air that it thinks its going to get. Neither of those things(EGR or canister) will purge unless the car is warmed up and under a light load.

 

 

Guy

[Bartman]

I think my problem is mostly or completely resolved!

 

I only drove it for a very short distance the other night when I thought I still had the problem, but I took it out for a longer drive last night after I changed the oil and filter and it seemed much better. The problem was almost nonexistent especially after I put together a couple of full throttle runs. Maybe the PCM had to go back in learning mode after all the problems were resolved.

 

I think there were mutliple issues as the problem became less severe after the iginiton wires and then seemed to go away after installing a new MAP sensor and connector.

 

I think the EGR is disabled because the 'EGR Enable, Min RPM' and the 'EGR Enable, Max RPM' are both set to 6375 RPM, but I haven't found a setting that would turn the CCP off.

 

I'll put some more miles on her this weekend and see how it does.