Sorting out multiple problems with different techniques
I hadn't planned on turning this job into a case study but it got interesting along the way so I am piecing all my info together for posting. This vehicle had multiple driveability symptoms despite previous repair attempts and lots of money thrown at it.
This vehicle and customer came to me on a referral from one of my regular customers. It had been around the block already and had the parts cannon fired at it, including a transmission. I had to sort out several problems and thought it might be interesting to post some different techniques I used to identify problems and confirm the fixes.
The customer said it was running and shifting poorly and would hesitate badly when starting off from a stop sometimes. It also had many warning lights on including, MIL, ABS and VSA. First thing I did was road test it and scan it. It definitely had some misfiring going on. It had an intermittent miss at idle and had at least a couple cylinders that would miss hard under load. It had a P0300 as well as a P0303.
My first test was a relative compression test to rule in or rule out compression early on. Relative compression looked good so I moved on. This thing had all new spark plugs and coils but I wanted to look at ignition anyway to see what it could tell me.
I didn't see any ignition faults but the ignition patterns indicated lean cylinders. There is no easy way to do an injector flow test on this car. No bidirectional and half the injectors are covered by the intake but, it does have a vacuum pressure regulator. I decided to try a seldom used technique to get an injector flow pattern. The setup (sorry no picture) is to pull the vacuum hose off the fuel pressure regulator and attach a vacuum pulse sensor to the regulator nipple. When the injectors open they cause a momentary drop in fuel pressure which cause the regulator diaphragm to move and pulsate. The idea is to compare the pattern each injector makes to identify differences in flow.
If you have never done this on a V engine it's normal to see 3 pulses that are bigger and 3 smaller pulses. This is due to the fact that one rail is further away from the regulator so the effect of the injector drop is less. The idea is to compare the injectors on one side with each other and look for uniformity, or the odd man out.
You can see that there is some variation in the pulses so I recommended to the customer that we try an on car injector cleaning.
As I performed the cleaning the engine seemed to run worse and after I was done the engine now had a dead miss on cylinder 3. I did another injector drop test to see what changed. As you can see, cylinder 3 looks much worse.
At this point I suggested we send the injectors out for ultrasonic cleaning but the customer opted to have me put a set of new injectors in instead. So the injectors were installed. The engine now ran smooth and strong with no breakdown under load, so I took another injector drop capture. It shows an obvious improvement. So that problem was addressed. I drove the car about 15 miles and it ran good, but that was not the end of it.
The customer took the car but came back in a few minutes and said it did the bad hesitation thing again and right now it's making a weird popping noise from the engine. I had them leave it again so I could recheck it. The noise appeared to be iac related, like it was bouncing of it's limit so I checked some pids. The warm idle iac counts seemed high at 27 so I did a throttle cleaning and idle relearn.
After cleaning and relearn the iac count was 6. That looked good and so far the weird noise has not returned.
We're still not done as I need to find out what is going on with the hesitation. The car has always accelerated fine for me but I believe the customer is experiencing something intermittently. Now the engine is running great and the only other symptom I notice is some driveline shudder after the trans shifts to second gear. It feels like a TCC shudder. But the customer said the car wouldn't accelerate and fortunately, the check engine light came on while it was occurring.
I now see a code P0132 Primary O2 sensor "High Voltage". Ok, now I have something to work with. I pull up datastream on my scanner and go for a ride. After a couple miles of driving with some starts and stops I suddenly experience the loss of power. I'm pushing the throttle but I'm losing power. I also noticed that if I held the throttle steady it would lose power, then accelerate for a second then lose power again, over and over.
I see an O2 sensor fault in the datastream that coincides with the loss of power. The O2 voltage suddenly goes high and stays there. The ECM is reducing injector pulse width and the rear O2 confirms that the ECM has driven the system very lean. I'm losing power because the ECM is taking away fuel. If you look at the injector pid you can see why it would lurch at times. The ECM would suddenly give max fuel and then cut it off. The car acted just as you would expect by looking at that data.
Back at the shop I inspected the O2 sensor harness wiring. I didn't find any wiring faults so I replaced the sensor and cleared codes. I drove the car again 2 different times for at least 20 miles. The car ran great and I never saw any more anomaly's in the O2 signal. I gave the car back to the customer.
4 days later I get another call. The check engine and ABS lights came on again but they didn't experience the lack of power issue. I checked it yet again and found an EVAP leak code. I replaced the rusted and leaking canister shut valve. I cleared the code and ran the EVAP monitor test. The test ran and passed.
It has now been 2 weeks since the evap repair with no further phone calls so I'm confident that was the end of it. This one definitely required some perseverance and an understanding customer. They were just happy that the problems were finally getting resolved. Hopefully next time I see it, it will just be for an oil change.
Sorry no, I don't own a gas analyzer at this time.
Good work Bob and thank you for the excellent presentation! Ray
thanks for sharing Bob , very good case study
Thanks for taking the time to write that up as I enjoyed it. Really impressed on the difference the new injectors made on the wave form !
I used to use that technique a lot years ago but not many cars have vacuum regulators anymore. There is always this option but I haven't bought one yet. Pressure pulse tester
Bob great write up. Your screen shots of the pulses at the regulator reinforce that you need to know what known good looks like to know what bad looks like. You can clearly see how bad the pattern is when you see the known good with the new injectors. Maybe a simpler way of saying it would be, if you don’t know what good looks like, how do you know what bad looks like? Good example of different
I bought the 'FirstLook Diagnostic Injector Sensor" years ago but I would not recommend it. Instead, connect a WPS500 to the fuel rail, bleed the air out of the pressure sensor and use the scanner to cycle each injector. Put lots of time on the scope to compare the pressure drop for each injector. But it won't tell you if you have a bad injector spray pattern. I like to diagnose lean or
Ray, you could absolutely find very restricted injectors with that method but I don't think I want to expose my transducers to fuel. It might make sense to buy a cheaper transducer for things like this where pinpoint accuracy is not as critical.
Great write-up. Do you think scoping the current ramps of the injectors would have shown anything or have you found the pressure regulator pattern to be more reliable?
The pintle hump will tell you that the injector winding is able to lift the pintle off of it's seat. But it won't tell you if the injector's screen is plugged or if the spray pattern is bad. Many engines don't have a fuel pressure regulator with a vacuum hose.
It's possible the pintle humps might have shown something but it was hard to get a good clean current pattern. I tried from the fuse box but there were other things on that fuse so the pattern was messy. There may have been another way to grab current but I saw the low hanging fruit of the regulator diaphragm so I went there instead.
Again Bob, excellent diagnosing and presentation! Ray
Awsome bob, this info will help me better my diagnostics thanks. Man what a head ache with this vehicle. you fix one issue then another arises and then another. I hope your customer was understanding of the situation. Not to turn this into a scope debate but how much do you like the escope? whats been your pros and cons?
Thanks Tom. As far as the scope goes, I have owned the ATS scopes from the beginning and I like them. They have some innovative features and were designed with automotive testing in mind. The main thing I would like to see changed is the screen real estate limitation. I would like to fill the entire screen with the scope window but right now a lot of space is taken up by the controls. Maybe in a