HISTORY. came in for loss of power. Test drove, seemed "not that bad" but was showing some random misfire. Never had a tune-up so did plugs, wires, cap, and rotor. Test drove, seemed a little better. Engine may have been colder at start out this time. Then, severe loss of power (finally experienced the original complaint) with much misfire, particularly on cylinder 2.
Tried swapping plugs from one position to another, then wires, then inspect new cap and rotor. No change. O2 sensor removal (upstream and downstream) yielded thread removal as well! Determined very high back pressure / plugged catalytic converter. Opened exhaust system before cat. Start and engine runs fine, revs much better, but then starts racking up misfire on 2 again. Both at idle, and when reving. Can hear backfire in exhaust each time it misfires. Remove cat, empty out the meltdown, re-install temporarily for test drive. Start vehicle, no more backpressure measured at O2 sensor. Do thread repair enough to insert a couple used o2 sensors (not correct ones, wires cut off, not connected just used to plug holes!). Test drive yields full power except when misfiring. Still pretty good power during misfire, just rough of course. Suspect possible burnt valve (was forced to run with cat plugging very much), lifter / cam problem, or possible fuel injector problem. Customer NO MONEY or desire to invest deeply into it anyway. Told her OK, drive it like it is, it will at least GO now. Will get her through until next emissions test, which will of course will take some serious money to fix for that! Also told her it needed a new battery, as the old one obviously didn't crank very strongly and failed a battery tester after having a charger on it. She informed me the visor vanity light was broken and the light is on all the time! So I removed the visor and cut the wire. Told her battery may be better now, but it did test as weak.
One week later. It's dead, needs to be towed. She ran it out of gas. Then after AAA added a gallon, battery failed. I put another battery in, add more gas, still would not start. Returned with some more tools, meter, timing light,. hit the starter and it started. Still misfire as before, then while reving it a little, it bogged out and I have never been able to get it started again. Even since hauling it here and all the testing below:
TESTING. much more concise here than the process! Fuel pressure within specs. Cranks and sometimes fires very little. Will sometime backfire through intake. SIGNIFICANTLY kicks back on starter while cranking. Just like old school when timing set too advanced. Spark looks fine. Doesn't seem to be flooding, more like no fuel or lack of fuel. Recheck exhaust backpressure. no problem. muffler not plugged. Compression test. a little low on cylinder 1, slightly low on 2, rest normal. I will get those numbers, but nothing that says this thing shouldn't at least run again even if not very well. Had injector unit out of it and bench tested it (albeit crudely but simply). At pressures significantly below what fuel system is actually delivering, all injectors will still spray fuel when 12v briefly supplied. I even got brave and very briefly cranked engine with injector mounted and plugged in, injectors lying on newspaper. Very briefly, but enough to see wet spots at the end of each injector. Also I had checked injector connector with vantage meter for pulsing. (all of this was weeks ago, so what I'm typing here is not the order I did things!) I have not been able to get it to run on starting fluid. Only much louder ear damaging backfire up the intake. no more with the starting fluid: ) WHAT?? HUH?? At a point when it was firing a little while cranking, propane seemed to increase the firing. As shot of gas poured down the intake also increase firing. 2 shots either eliminated firing, or it was just done for awhile anyway as is sometimes the case. Also, crank sensor and distributor signals appeared present with vantage meter. I tried a new crank sensor temporarily to no avail. Now, I have a
2000 Blazer I can borrow from, might try swapping distributors. Not sure if PCM is the same for swapping, I suspect it is not quite interchangeable?? The most recent thing. with Snap On MODIS looking at pid graghs. I see that while cranking, injector pulse width is ZERO. But vantage meter showed pulse. Test light doesn't flash but dims (it's incandescent) so I just use meter instead of test light for that check.QUESTIONS:
- Should PCM data show injector pulse width during cranking, or does it only read / process that information after it's running? (I guess at some point I can sabotage the Blazer so it doesn't start right up and compare. But I won't know if my sabotage vs. the Jimmy's problem should yield the same result).
- Is PCM interchangeable between 1997 Jimmy and 2000 Blazer? (Distributor? ICM?)
- Does the typical small bottle propane torch deliver enough propane to run a 4.3 v6 engine?? (I have a grill size tank and regulator I could use. : ) )
- What should the ignition timing actually be firing at during cranking? I made a big crayon mark Bottom Dead Center of the crank pulley after finding TDC via cylinder on compression stroke via borescope in the plug hole. BTW, distributor timing dead on, forgot to include that above. It fires at TDC while cranking. I wouldn't think TDC would kick back on starter. Maybe it's starter / ring gear causing that. Shouldn't good spark at TDC start ok?
- I read somewhere about distributors testing fine can still causing crazy problem regarding fuel injection. Vantage meter is very vague regarding only showing what wave-form should be shaped like. Anyone have greater detail testing for this situation?? Has anyone heard of distributor signal (or ignition module or PCM) being being able to cause a persistant misfire on one cylinder?? And/or then ending up as a crank no start problem?? It's a 97, but body and interior clean. It's worth a certain amount to fix, but I don't want to upgrade the fuel injection on an engine with a valve problem. It would be nice if a single problem fixes ALL. Then it still needs a cat and o2 sensors. So without better diagnostic, it's going to end up as parts and scrap!
OK, compression numbers
1 90 2 130 3 155 4 150 5 150 6 148I've seen worse figures on engines that still run perfect. I squirted oil in cylinder 1 and cranked some more. Got up to 105. Cranking (this engine has seen a LOT of that lately). really seems to be lacking fuel. Next time I work on it (may be a while, it's outback now), I think I'll try shorting the coil wire to ground and see if it still kicks back on the starter. Hoping some GURU's out there have some deeper info I can utilize. Be it the 5 questions above, or other suggestions. Thanks all!