Hard Starting 6.2

[Mark K.]

Hello Everyone,

I've tried to go through the vast archives here to find an answer to my problem but am still scratching my head. I have a great old 1988 K30 1 ton 4wd with a 6.2 that I have owned now for almost 10 years. It has just over 100K and has always been a great truck. I am currently having a hard starting problem though that is really giving me a fight. When I first go to start the unit when cold, it will fire normally for about 5 seconds (just like a normal start) but then it dies. It then takes minutes and minutes of cranking to get it to fire again, almost smoking the starter in the process. I sense there is perhaps an air leak somewhere in the fuel delivery but am unable to find it. Once I get the truck started it will start ok within say a few hours but it if sits overnight I once again get the problem. I have over the last 30K miles installed a new injector pump and timing chain, new lift pump, new filters and most recently new glo-plugs. The glow plug controller seems to be cycling normally but it is original equipment and is getting a little old. I have checked for loose lines at the injectors on the heads, also at the injector pump and also the lines too and from the filters. Can anyone give me any hits on this thing? I did replace the lift pump not to long again but again that could be bad perhaps. Also can anyone perhaps point me to any old archive areas on the site that I might could reread that address this topic. I know this issue has come up before. Thanks as always and thanks too for the great site,

Mark in Baltimore

[More Power]

Sounds like you've got a fuel drainback issue...

This can be caused by excessive vacuum in the tank (defective cap), and/or exacerbated by a bad check-valve in the mechanical lift pump.

Try loosening the fuel tank cap after parking it the next time.

Jim

[Ratau]

Jim

I got the same problem with the tank cap, forms a negative pressure in the tank. Do you have any idea at what vacuum must the vacuum breaker open?

[Mark K.]

Ok, I checked the gas cap and that looks ok, no difference with the cap off or on. I then disconnected the main fuel input line from the lift pump up at the block assembly where the large rectangular main fuel filter is location up on the firewall. Pressure looks good and the check valve looks ok too. I rechecked the glow plugs with an old glow plug and those also seem to be working ok. A quick question though, the "block assembly" up on the firewall that the main fuel filter attaches too, it has a number of wiring leads coming out, at least one of which I suspect is the water in fuel warning indicator, can that block assembly go bad and then block the fuel to the injector pump? Also does anyone know are those "filter mounting blocks" off the military trucks also perhaps the same as the civilian versions (same or different voltages)? If so I might have an old one of those laying around. Thanks again for the help,

Mark

[wvo]

For what it is worth my truck did the same, run for five seconds and then stall thing to me the other day. Then it wouldn't start at all. I read somewhere on this site that a slight vacuum in the fuel system is normal after shutdown and if one of your injector lines is leaking a little, then you will get air drawing back into the system. I have noticed that the truck had been spitting a little white smoke on start up lately which may also be due to a leaking line. I had to replace one of the injector lines a few months back because it had rusted out, so maybe I have another one ready to go. The rusted out one was easy to find since the truck was running a little rough and when I investigated, there was a steady drip/stream of fuel coming out of the conection. Anyway, the other day the air must have backed up to the injection pump and air-locked it. So I cracked a few injector line connections and had to crank it for three counts of ten. Then the fuel started to weep out of the connections and after I tighten them up it fired right up. Just in case you need a fuel line, I got mine from www.dipaco.com. (http://www.dipaco.com.) They sold me the individual line I needed for a fraction of what the dealer wanted.

[BC Clark]

Another thing to check since you have an '88. If you still have the pressure (vacuum) switch in your fuel filter base you need to get rid of it. I had the same issue with my 88 Jimmy. This is discussed in the trouble shooting guide under both hard starting and the fuel filter section. GM got rid of it in 1990 and issued TSB 90-6C-45 to remove it from from the earlier units. It solved my start and die and crack-crank-crank problem. It is part of the outlet side and when the diaphram in the switch or the o-ring around the switch fails it leaks air. Surprisingly mine did not leak fuel when running, but it sure was a source of air. It's a simple operation, but is easiest with the unit removed. Remove the filter, pull out the switch (A circular unit about and inch in diameter held in with a sheetmetal spring clip) tap the hole and put a screw in. I used a little gasket sealant. Just remember you are on the output side of the filter, flush and blow all chips from tapping or these will go straight to the pump.

[Robyn]

I have an 84 Blazer that does this same thing.
If I park it nose down its fine.
This issue is beacuse the fuel lift pump on the engine has a faulty check valve that allows the fuel to drain back sucking in a air pocket and messing things up. Replace the fuel pump on the right front of the engine and the problem should be solved

[ZZ]

I had this same problem last winter (2004). My truck was a bitch to start every morning. I changed fuel filters & lift pump and checked all the connections I could find. I finally put it in the shop and they found out that the hose was cracked on the little drain valve beside the "goose neck" They cut off the end of the hose and put on a new clamp. It has started like a champ every morning since.

I had a day or two of these same symptoms after it got cold this year. A new fuel filter cured it this time.

[arveetek]

This hard starting issue sounds just like classic air lock. A lot of the usual suspects have been covered above. Another source of air in the fuel system is cracked rubber lines. Sometimes a hose can look great on the outside, and it won't drip fuel, but will still allow air into the system. A great way to check out the whole system is to pressurize the fuel tank with air.

Take an old or new fuel cap, drill it out and install a valve stem. Then you can pressurize the tank with an air tank. Don't go crazy, only a few psi is needed to help you find the leak. Look for dripping hoses or hissing air.

Casey

[More Power]

Ratau, The pressure relief valve in these diesel fuel tank caps are supposed to vent once 2 psi of pressure or 2" of vacuum exists. So, there should never be more than 2 psi or 2" vacuum present inside the tank.

Assuming the barometric pressure remains constant, pressure changes inside the tank are caused by expansion or contraction of the fuel as a response to a change in temperature. A full tank of fuel along with a significant temperature change will produce the biggest pressure/vacuum change.

Jim