I'm thinking that the full throttle shift point test is a bit severe (almost 5000 rpm) and also difficult to catch the absolute max air flow if scan rate is slow (since rpms are climbing) I'm thinking that dual-plotting or a log of rpm vs air flow would be useful. Also would be cool to throw in vacuum and throttle position if scanner is fast enough to do 4 pids with decent frequency. Yes of course it is a rule out test!!

 

Looks like I'm not the only person who has this idea!! Found a really nice write-up here with a link to a quick and dirty VE calculator at OTC web site. https://ricksfreeautorepairadvice.co...ficiency-test/ What do you think George, is this sticky material? If so, I'll write something up that includes this link as well as a not-so-quick-and-dirty (but more exact) way of calculating VE using numbers from a density altitude calculator that accounts for elevation, barometric pressure, and humidity, as well as air temperature. https://airdensityonline.com/us-track-list/ Probably overkill, but it's all interesting to me. My Blazer came out 83.5% VE (88% by quick and dirty method) at 4000 rpm this morning, which is well within the 70-90% range given in the first link. It has the original catalytic converter and 120,000 miles. In reality, this really does many of the same things as the running compression test, but is a heck of a lot easier to do.

Going to have to find my little bluetooth OBD2 adapter. Had to use the Vident scanner this morning and it only read out 2 significant figures for the MAF (0.30 lb/sec). g/sec would be better accuracy as this converts to 136, plus I'm able to log and plot with the phone apps.

 

Les

yes, I think this is definitely worth the effort, more advanced members should find this useful and less experience members will learn something interesting.

George

 

Hello everyone, sorry I haven’t been working on my vehicle lately I’ve been so busy. I put a bottle of Techron fuel system cleaner in and it is running a lot better. Also, I’ve already have run a couple of tanks of gas and the acceleration is staying consistent and I have more power. Also I’m seeing the typical normal flame burn pattern on the plugs on number 1 and 2 cylinders.

 

Hello everyone, I spoke too soon I’m now getting a reoccurring p301 code. I’m sorry I forgot to mention when I got the truck I did have a p301 code for several months that I chased and could not figure out. Compared to then I do have a lot more punch in my acceleration and my hot restarts are good since using the Techron cleaner. I’m nearing my emission inspection time and I have to get this fixed by the end of the month. Also I noticed the following below:

1) Before when I cleared the codes the p301 code would stay off for several weeks of 10 to 15 miles of commuting

2) Now the code will come back within 5 miles of driving of mixed highway after repeatedly clearing the codes. I do notice that the p420 code has not been coming back several times, I just can’t get the p301 code to stay off.

3) I still have to do the exhaust back pressure test, can I just use my vacuum gauge with a threaded in bung after the catalytic converter.

4) Also, could this be caused by the factory recommend 5w30 oil that I am using is somehow breaking down when the engine is warming up and causing a compression loss. I am using Mobil 1 and I do have to add a little oil like every once in a while. I can’t tell if it’s leaking or burning because I did do the valve cover gaskets like 3 months ago. Also I did the oil pan gasket and oil pressure sending unit when I got the truck 2 years ago. There is no smoke and I have to approximate it to be like a 1/2 qt every 1000 miles.

5) I was thinking about going to a thicker oil like 5w40 Mobil 1 European Car Formula. I have almost 200k miles and have had good luck with this oil in my 1988 305 tbi engine that has about the same mileage. I’m just worried about spunned bearings due to the thicker 40wt and the additive package for this oil which is for oil burning German cars to possibly harm the catalytic convertor. I don’t mind adding oil once a while and the car doesn’t knock or tick.

6) Also could the knock sensor be picking up some vibrations from worn motor mounts or maybe a worn harmonic balancer and are the misfires reported to the computer by the crank sensor ? There is no shake at all when cold which is when the most fuel is demanded so when it warms up into closed loop less fuel is demanded

I will definitely finish the instructions you guys provided for compression and coolant pressure test, I just have been so busy. I would greatly appreciate your thoughts

 

I was looking into the dynamic compression test and it mentions that you must disable fuel and spark to that one cylinder in question. This would be not possible I'm guessing because of the spider injector pod plug connects to all injectors at once and not like a fuel rail with individual Bosch style injectors.

Couldn’t I just use a leak down test?? I’m having some second thoughts, I honestly think it could be a lower or upper intake manifold gasket. It has a lot of power in cold damp weather even with the engine shaking a little bit. I do recall over the summer that the acceleration was a little weaker when hot and dry. I’m not losing any coolant and the exhaust back pressure gauges available on the market are only within 0-3 psi of measurement range. 3psi being the most restrictive and 0 psi being a perfect running engine. How could you have such resolution with a cheap amazon pressure gauge. I’m definitely not going to buy an expensive Ashcroft gauge with more resolution below
https://www.jegs.com/i/OTC-Tools/717...hoCiGIQAvD_BwE



Wouldn’t a vacuum gauge connected to manifold vacuum be a better test for exhaust back pressure. In closing is there a definite test for leaking intake gaskets other than spraying water or carb cleaner on the manifold
Here is a link on YouTube from Eric the car guy

Here is also some graph pics from my scanner of the MAP sensor at idle and the MAF sensor at idle along with just revving the throttle. I think the graphs look a little weird or maybe I’m not interpreting them correctly.





I would greatly appreciate some thoughts.

 

The vacuum test is OK. The definitive test is an exhaust back pressure gauge in a front O2 port. A shade tree test is remove a front O2 sensor and see if it runs better.

If you want to get good MAF numbers. Record at idle and either the full throttle 1-2 shift or Les' brake torque method (not in front of the garage door).

Compare your MAP reading at key on to the local weather report.

George

 

I went ahead and did some more research and converted the values for MAP and MAF and they are about right where they should be at idle. I also hear that it could very well be a lower intake manifold gasket as opposed to a plenum gasket leak which would make a more general vacuum leak that would hiss loud at idle. I was thinking about smoke testing the engine. I don’t want to buy a an expensive pressurized smoke machine, I heard about using a cigar. Also, I might even be tempted to pull the heads and redo the valve stem seals and hand lap the valves. As I recall when I did a 350 vortec it wasn’t much more to pull the heads and it might already have the horrible abs plastic intake manifold gaskets that like to fail and mix oil with antifreeze. I will be using the Felpro steel and rubber Permadry plus intake gaskets.

 

If you are considering pulling the heads, have you at least performed a std compression test on all cylinders?

George

 

Here is what I got on a cold engine with no accelerator pedal pushed down, I believe this is the correct way??
1)180
2)180
3)182
4)182
5) 182
6)183