1993 S10 Tahoe 4.3 CPI - cranks, no start
 

New to the forum (nice place!), any suggestions appreciated.

My truck has been sitting for about 4 years, parked it due to a bad fuel pump. Dropped the tank today. Drained the old gas, installed the new pump and reinstalled the tank. Also replaced the fuel filter. Put in about 5 gallons of fresh gas.

I cycled the ignition on several times to charge the fuel lines and then tried to start it. She cranks but no start. Thanks to some of the info I found on this site, I believe the fuel pump is working - I can hear the pump run for a few seconds when the key is turned to the on position. I also checked the pressure at the shrader valve in the fuel line and the gauge shows about 62 psi when the pump energizes. The pressure holds (within a pound or two) when the key is turned off.

I've checked and the plugs are sparking although they do appear to be a bit carbon fouled.

I'm stumped and not sure what to try next. Any suggestions?

Whats the battery voltage and hows the alternator?

The battery is new. Measures 12.4 volts across the posts. The alternator seems to be ok visually, correct connections, connections tight, etc. Would it be worthwhile to pull it and get it tested?

This morning I tried a shot of starting fluid. It sounds like it starts but within a few seconds it stalls out, likely when the ether is burned up. Makes it still sound like a fuel delivery issue, but I'm not sure what to check next....?

You may have to pop off the upper plenum to see if you may have a problem with the injector electrical connector on the CPI spider.

Thank you sir. That will be my next step then. Stay tuned.

I removed the upper plenum and now have access to the lower manifold area and it's parts. If I understand correctly, the CMFI assembly is mounted in the center of the lower manifold and is the main injector unit that feeds gas to the 6 individual nozzles..........?

Visual inspection shows nothing obvious - things are dry, the "spider" appears to be intact and the wiring harness connector appears to be firmly in place.

Is there a way to test the CMFI assembly or perhaps the wiring harness? Not sure what to check next...............

Thanks for the help so far!

If that gas has been sitting in the tank for that long chances are the gas is gummed up in the CPI unit as well and not letting any gas get through the popets.. Replace the spark plugs and try it...then smell the plugs to see if you are getting any good fuel.

Here's where things stand today:

I replaced the fuel regulator. I checked for leaks with the ignition on - no leaks. fuel pressure on the rail is 61 pounds. I re-installed the upper plenum using a new gasket. Replaced a broken vacuum hose on the back of the upper plenum. Re-connected MAP, IAC, TP sensor and the valve on the top of the plenum.

Installed new plugs, gapped at .45.

Gave the key a turn and it started with a VERY low idle and after a few seconds went dead. Before, it just cranked, but now it sounds like it's trying to start. It almost catches but not quite.

For kicks I checked for codes. I get a 12, 22, and 34. I think the 12 indicates the diagnostics are good.....? I believe the 22 is the TP sensor and the 34 is the MAP. I backprobed the TP sensor and I get 4.88 volts reference signal from the gray wire, and .65 volts from the blue wire with the throttle closed. When I gradually open the throttle the .65 volts climbs until it hits 3.98 volts at wot. Based on this the TP sensor seems fine. I haven't checked the MAP sensor yet.

Regarding the possibility of the popit valves being gummed up from sitting so long - is it possible I could soak them in Seafoam or somthing similar to un-gum them? :icon_shrug:

Thanks for any help!

Some success! I pulled each of the popet valve assemblies out of the lower manifold and spray cleaned them with throttle body cleaner. Re-assembled everything and she fired up. I's running quite rough but will run and idle on its own. Getting it to start was half the battle, tomorrow I'll tackle the rest.

Thanks to those who offered advice, I appreciate it.

I am having this same problem with my 94 blazer , but mine was running fine , and the fuel pump went . changed that , ran for awhile then quit again now it will start every now and then . I also put another fuel pump in and a filter still the same thing. Update . When I changed the fuel pump I must have messed up the fuel gauge says it has a little over a quarter tank . I found this out after a trip to the salvage yard and new spider injector was installed . Still no fuel going through it , but I had fuel to it, so I never thought to check the fuel level . DUGH . But she is alive finally , But any way , as I found out the hard way the 4.3 needs gas in order to run . Not putting my name be this post , Thaanks