2002 S-15 Sonoma with the V6, truck stumbles and stalls on brake application, much worse at night when the headlamps are on. Have replaced tge TPS, AIC, Fuel Filter, Plugs and wires, ignition coil MAP sensor and the fuel pump. On nice days she runs great as long as I set the idle high, now when warm runs fine till throttle application in gear and truck moves and engine dies like shut off. Any assistance or ideas appreciated.

 

Welcome to the forum.

Do you have any codes?

The first thing that comes to mind is a vacuum leak since your brakes are vacuum assisted. Have you done any work on the vacuum system or checked for vacuum leaks? Have the LIM gaskets been replaced on this motor? How do the brakes function?

Worse with headlights on suggests system voltage. What is your resting battery voltage, voltage during charging, and voltage when it dies?

George

 

Brake function is fine as long as the engine supplies vacume, I went over the vacume lines and blocked off the non brake ones as a test and things were better until it entered the night. When it went back to the same thing. I am waiting on a voltage tester from Amazon (Baffin Island you understand) but I will run a recording on the voltage via the OBD and post them this afternoon. It only does the brake apllicatiob stumbles in gear when moving, when stopped its happy as a clam even in gear.

 

Wow, you are in a really remote location. Probably not too many Blazer owners where you live. LOL. I lived in Ontario for a while as a young boy but your area is an entirely different thing all together.

Does your scanner have live data capability? Do you have any ODBII trouble codes?

Do you have a vacuum gauge?

George

 

The scanner does a live run of data points but it his hard to interpret. It looks like everything is operating correctly and then there is a sudden drop out of everthing. I do not have a vacume gauge but I may be able to acquire one.

 

What do you mean that there is a sudden drop out of everything on the scanner live data?

Run your truck in park until the fuel control system enters closed loop as shown in live data on your scanner. This means that the engine has warmed up enough that the PCM is now using the O2 sensor data to determine the fuel injector pulse width and hence the fuel delivery amount. Write down your fuel trims at idle and again at 2500 rpm. This will help us determine if you have a vacuum leak without using a vacuum gauge. At each rpm you need 4 numbers, so 8 numbers in total. ST and LT fuel trims for each of 2 banks, showing the +/- sign for each. Example:

idle 2500rpm
STFTB1 +8.0 -1.5
LTFTB1 +4.0 +3.5
STFTB2 +7.0 -1.1
LTFTB2 +5.5 +5.0

We will discuss what the numbers mean after you report them.

George

 

I forgot to mention to watch this fuel trim data during an event where pushing the brakes causes engine problems, in park of course.

George

 

Ok Attached is what I get from my Logging software, I know the GPS stuff is all out and of course it ran great while I was driving it, Although I did get the flashing Misfire light on Cylinder 2, as that is the one behind the steering that plug was clearly not replaced by the local mechanic when he charged me, I will replace it later. FYI the highest speed limit here is 50 kph and the truck averages 30kph around town. I had until this test never had it at 2500rpm long enough for there to be recorded missfires and even that was not enough to turn on the light, just the flashing warning. The STFB average the scanner shows on the display wanders all over tho. I am using torquelite on my phone for my scanning, should I go to a different program for the data interpert?

I did find running it at 2500rpm made it feel "Happier" no sign of the usual braking issues.

 

There is a lot going on here so I need some clarification:

1) So braking causes the engine to stumble or die but only if your moving? If you apply the brake in park or at idle in gear there is no problem?

2) The problem is worse when the headlights are on (day or night) or the problem is worse at night?

3) When its warm it stalls or dies when you try to accelerate in gear from a standstill?

4) You are registering misfires in the live misfire counter? How many misfires do you have? Is it only #2?

5) Do you have any ODBII fault codes stored? What are they?

6) What do you mean that your live data suddenly quits? Its a phone/software problem or the ODBII computer interface stops transmitting data?

6) Why did you replace all of those components?


George

 

Clarification (And thank you so much for the help)

1) Braking causes a drop of rpm on initial sudden application, causing a stall, often with light application the rpms do not dive as far and the stall can be prevented. This only happens in gear and in motion. When stopped truck seems fine and idles well.

2) The problem is worse at night, but on dark days it happens leading me to look at the Lighting system

3) When it is warm it had been fine until the last few days when warm or cold it will randomly refuse to move more than a few feet under power without stalling. but in idle sitting it is happy

4) When the missfires came up today the engine light flashed and the scanner reported misfires on #2 exclusively. when I visually checked it it was clearly older than the other new plugs and was probably skipped by the local shop who I have found to be crooked.

5) No codes stored the "RPM Higher than expected at idle" comes up occassionally as I have increased the standing idle to give it a better chance to not stall which seems to have worked somewhat.

6) The data to the scanner just stops, I think it may be an issue with the scanner used as the scanner seems tempremental about operation.

7) As far as component replacement, it takes 2 week+ to get parts here and I have been reading up to try and get it running regular. As shipping here is always very high I tried to package things together that could be possible causes and have been applying them as things continue. The MAP Sensor solved it for about a week and a few days to a week with any of the others. My feeling is there has been issues with these components (The MAP for example was clearly leaking due to a torn up gasket) There is some broader issue still in the background.I have new battery cables (Positive and Negative) as my next "Planned" step but I feel like they may have been misrouted by the previous owner and I am trying to locate a solid diagram of placement online as my Haynes is not illuminating me as I would like. As there are a large number of these trucks in town finding a home for parts I do not use should not be an issue.