Ran great then wouldn't start. (OPS maybe?)

[Big Red Suburban]

Well, the suburban wouldn't start the other day for the first time (it had been running earlier and was only off maybe 15 min). It would crank just fine, but no fire. Tried a couple of times, let it sit 5 min, tried it again. Still no fire. Borrowed a car to get the family home (we ended up missing the 4th of July firework show - kids weren't happy!)

Once I found some time I did a search on this forum, read all I could, and went back to troubleshoot two days later. I pulled the ECM B fuse to see if it was blown, it wasn't so I put it back in. Tried to start it again to make sure the problem was still there and it fired right up.

I went ahead and checked the lift pump for pressure at the fuel filter and had 4 psi. For good measure I went ahead and replaced the OPS. It seems to me that if something was going to intermitently fail, it would be the OPS rather than the lift pump?

I guess I will see if it happens again, and if it does (and I am the one driving) I will immediately check to determine if the lift pump has flow to the filter.

Any other ideas?

[AndyL]

Sounds like the FSD to me. Probably heat soaked from the hot engine during the 15 minute off period.

The OPS only controls the lift pump, should still start without it. My truck ran without the LP for who-knows how long before i noticed it wasn't working!

[tom.mcinerney]

Big Red- When transistor-driven circuits crap-out, the transistor(s) often fail in ON position. Both the FSD and Lift Pump may do this. Their power is fed thru contact on ignition switch, which may be due for replacement.
Not to be too negative, but the classic LP indicator is 'warm start, stall'. If the FIP is worn out, it will first give indication by 'no start, warm/hot'. That is , FIPs first fail by not starting hot, because when the pump and the contained fuel are hot, the viscosity of fuel is too low for worn components to be able to create adequate pressure to 'pop' the injectors....A check for this is to carefully pour a glass/vase of room temp water over the pump, which may cool it enough to allow engine to then start up. This seems risky, that it might stress the cast iron below; it has been a successful test, though. And sometimes it'll temporarily help a hot FSD.

A good initial effort includes inspecting DTC codes, they can narrow down the list.

[HammerWerf]

Big Red,

I had a similar event with my 1984 pickup yesterday(7/7/04) (mechanical 6.2). Drove it home for lunch, ran great,

40 minutes later tried to start it up. Engine turned over, but no fire. The turning(cranking) speed sounded slow, so used the other pickup to get back to work.

Returned home, checked the batteries. Knew I had one that was about three years old. Here in the Central Valley, batteries have a life expentancy of about 2 years. Heat kills the batteries fast
around here. I learned this from my brother-in-law who works for Sears. Sears did a study on
battery warrenty replacements and noticed that hot summer climates kill batteries the fastest.

With the engine cooled off, engine started up at slower cranking speeds on the old battery.

Replaced battery, and the engine started right up. Cranking speed sound like about twice what it was.

The old battery voltage was 11.6 volts on my trusty VOM meter. New Battery 13.1 volts. I had
a bad cell and apparently no capacity available.

Might check the batteries to see if they can be excluded from the list.

HammerWerf

[Big Red Suburban]

I checked the codes yesterday which didn't reveal anything. It hasn't happened again yet. I think the batteries are fine, it cranked over just like it always did when it wouldn't start.

I went to Sears yesterday and got an infrared thermometer so I can check the temp of the FSD. After my drive to work this morning it was 150 degrees. I may try a series of 5 mile runs later today, turning off the engine for 5 or 10 mins after each run to let it heat soak the FSD for a while. I'm curios to find out how hot the FSD gets or if it experiences the problem again.

This infrared thermometer is pretty cool :D

[Big Red Suburban]

Man is it hot today. 95 degrees with about 90% humidity. Anyways, after my trip home (25 miles) the FSD was 182 degrees (intake was 150 degrees), let it sit with the hood closed for 10 min, checked it again and it was 180 degrees.

I went to town (6 miles away), checked it, 162 degrees, let it sit with the hood closed for 10 min, it was 167 degrees.

The no start condition has not occurred again, however on my home from work I noticed the boost level seemed to fluctuate more than usual, drop off from 6 to 3, then from 5 to 2, etc. The changes were sudden as I was slowly applying more thottle or holding steady (rpms around 2000). It seemed different. Then on my trip to town the boost dropped from 6 to zero and the SES light came on, it later went out and the boost came back. This occurred maybe 3 times on my way to town.

I checked the codes while I was in town and got a 78 which is the Turbo Waste Gate Solenoid Fault. I must be loosing vacuum somewhere which is letting the waste gate go open? How much vacuum should I have at idle and where should I check it?

[Big Red Suburban]

I tried to move the waste gate actuator arm by hand with it idling and I couldn't do it (did not move at all with as much force as I could get on it without burning my hand).

Next, I followed the vacuum line from the vacuum pump back to the top of the drivers side valve cover and found a connection which looked like it was coming off. I forced it back on and took it for a drive. The SES light did not come back on the and boost seemed back to normal, no more quick dropping off when it should have been building up. I think I got this problem fixed.

I did check the pressure again at the fuel filter drain fitting and top fitting. Both read 3.5 psi with the truck idling? This is with a hot engine on a hot day. I thought I read somewhere it should be above 4 psi? What is an accetable range? 4 psi to 8 psi? If so I should probably replace the lift pump to prevent the injection pump from working even harder?

Thanks...