another hard starting thread! Sorry.

[Subzilla]

Vehicle: '83 6.2 Sub, 262k miles, at least 140k miles on injectors, 30k miles on IP

Symptoms: Use to start in a second or 2 but starting a month ago all at once, 3 to 5 cranks are required to start the engine after sitting for 8 hours or so. Not very dependent on outside temps. The engine will fire then run for a short second (or rather the rpm's suddenly burst up) then die, almost like fuel starvation problems or air in lines. Once started, it runs perfectly fine and will easily restart. No other symptoms once running.

Diagnosis items performed:
1) GP's checked good with test light. Pulled about 4, connected to harness, hit the switch and they glow orange.
2) Changed both fuel filters
3) Put clear tubing on IP at return. No air bubbles while running.
4) Cracked 4 injectors, turned over engine till fuel weeping. Closed and engine still took extended start time.
5) Pulled line off of electric fuel pump (installation per Doc Lee's design), hit switch and it pumped lots of fuel into container.
6) Replace all injector return lines with Viton including end caps. Replaced other fuel lines in engine compartment with fresh ones.
7) Visually checked fuel lines on top of fuel tank for leaks. Don't see any
8) I do run biodiesel but I ran the tank almost out and added 10 gallons of petro just to make sure. No change in starting.

I keep thinking air in the lines but the tests seem to eliminate that. Could it be more complex or internal with the injector pump or injectors? Thanks!

[DmaxMaverick]

......Could it be more complex or internal with the injector pump or injectors? Thanks!

Yes, but....

Injectors or the pump can drain back while sitting. This usually requires some vacuum on the system. Check your filler cap. If it's retaining vacuum (not venting), the vacuum on the system can/will allow air to be sucked into the system. If it's a fuel system vacuum problem, it will usually be worse with less fuel in the tank.

As a diagnostic process, try loosening the fuel cap at the next shutdown. If the problem goes away, replace the cap. If the problem is reduced, you could have injectors too worn, allowing gravity to syphon down, and pull air into the injectors. Again, this can be worse with less fuel in the tank.

[Subzilla]

Still testing your theory on the gas cap. Each test takes a day as I have to try something then wait for cool down & time! I tried the gas cap on the last run and I think it started quicker yesterday. I'm trying it without loosening the cap, again. I think I may also have my injectors tested after reading your post and Robyn's injector explanation over on the 6.5 section http://72.22.76.69/tdpforum/showthread.php?t=27245

Good reading.

I'll post my results.

[Subzilla]

Update: My hard starting issues were because of the high percentage of biodiesel plus maybe some high mileage engine wear and old injectors. I reduced the percentage to about 70% biodiesel and the crank times in both vehicles went from 4 to 5 ten-second cranks to one good 3 to 6 second crank. Still not quite as good as when running petro diesel but I'm happy! The $pg is much better but I do realize that biodiesel has lower BTU's then dino juice. I'm pulling the Sub injectors this weekend to have them checked and will eventually check compression. The Sub now has 265K miles and the Blazer has 255K. At least I know my glow plugs are good and I have no air in the lines after all the diagnostics I did!

[Robyn]

The injectors need to be in top shape to atomize the veggy juice to the point that it will burn.

Get the shop thats doing your injectors to make sure they are popping at the top of the spec and that the spray pattern is good too.

Once you get this issue in good shape the other thing is of course the IP.
The advance needs to be working very good as does the pump itself.
make sure your timing chain is nice and tight so all the adjustments are right to spec.

Veggy goo is not nearlly as flamable as regular go juice so herein lies part of the issue.

Couple this with poor pop pressure, poor spray pattern and maybe slow timing and the issue translates to a hard start condition.

Heat is everything when it comes to getting these little beasts to fire off, especially when cold.

Good luck

Robyn

[Subzilla]

Robyn, I love reading your replies. Your lingo always entertains me! Veggie goo...

I pulled the injectors out yesterday and will ship them to Tim Wagner at Accurate Diesel (TDP supporter). I put on one of his pumps about 3 years ago but my injectors have at least 140k miles on them - they were in the vehicle when I bought it. I installed timing gears the same time with the rebuilt pump installation.

Thanks for the reply and I'll make sure Tim checks the "squirts" for the top of squirting spec. I'll update with the results.

[Subzilla]

Injector test results are as follows: "They pop at around 1650 PSI - compare to new nozzles at 1810 - 1960. GM's minimum spec is 1520. They don't pop quite as crisply as a fresh nozzle, and may tend to leak a little 200 under pop pressure, which they should not, but at most, they only show normal wear."

What would be ya'lls opinion for replacing the injectors based on the test results? It appears they are still above the border line. I've had these for as long as I've had the vehicle (at least 140k miles) but as spelled out in my previous posts, I'm trying to improve starting times and power.

Thanks!

[DmaxMaverick]

GM's minimum pop pressure is based on warranty replacement. That alone should tell you something. 1520 is way too low. If you are getting leakage and low pop pressure, they're due. "Normal wear" also means "worn out - normally". Sounds like time to refresh or replace them. They won't heal themselves, and only get worse from here. You'll be impressed with the difference of what you have now and a healthy set.