2.8 TBI V6 - Won't run with MAP conn. after TBI rebuild

[armyBob]

Pulled the o2 sensor this morning while waiting for a ride to work...It came out easily, thank goodness. Still won't start, so I don't think I melted the cat, but it might still be flooded from yesterday, so tonight I will pull the plugs and run a compression check (pressurizing the cylinders seems to vaporize ?? the excess fuel and help dry them out - it comes out of the release valve on my compression tester).

Even if it was flooded, with the o2 sensor removed, would I be able to feel vacuum while cranking (with my thumb over a vacuum line)? I got nothing...weird.

I am also going to try a new ignition module and pickup coil since the spark wasn't blue.

Thanks for everyone's help so far.

[armyBob]

Um, if the spark is orange should I try a new coil or a new ignition module? I'm thinking coil.

[Guest]

I too was going to suggest a different port, after reading your reply to my previous one.

It sounds like you are on a 'ported' vacuum source, where there is no vacuum present at idle (throttle closed). EGR is NOT manifold vacuum, it is ported vacuum. IIRC there is a vacuum port near the base of the TBI or on the manifold itself for the MAP sensor.

[armyBob]

Right, that's the "stock" connection for the MAP, between the fuel lines. But for kicks I tried the EGR port (i thought the only ported vacuum source was for the EEC canister). I can try the port for the HVAC/thermostatic air cleaner/AIR pump. The other one is connected to the EGR (and of course there's the PCV and brake booster).

This thing is driving me nuts! I know there's an answer somewhere...

[geoffinbc]

Run the engine with the ESC wire disconnected. Run With the ECT disconnected. Report back

[armyBob]

Roger, I have the MAP connected correctly (the hose is too short to go anywhere else!). I cleaned the TBI well, and the port is not blocked.

I'll try disconnecting the ESC and ECT. I think I already tried it with the ECT disconnected, but I'll give it another go.

One thing, I think the gasket in the rebuild kit was of a slightly different design than the old one (i don't think I have the old one anymore). Mine has an open space between the two TB bores (right where the map port is). Are there two different types of Model 220 TBI out there (on the 2.8 - I realize the 4.3, etc. are similar with larger bores)?

[geoffinbc]

A gap between the bores will not make a difference. However on a GM gasket the bores in the gasket are seperated.

[armyBob]

Gasket looks the same as the Isuzu one at Advance, so that's not it.

But...I did get it to turn over! (without the MAP connected again). I left the spark plugs out overnight so the fuel would evaporate, and left the o2 sensor out in case there was a blockage. I tested compression on cylinders 5,6, and 4 - they were high, like 180 psi. I said "screw it" and cleaned the plugs, put them back in, disconnected the MAP sensor electrical conn. and put the fuel pump fuse back. It ran, but I think it backfired into the intake - it popped my PCV valve out of the valve cover (?Not enough backpressure?). Turned it off, put the o2 sensor back in (after cleaning it with a torch and wire brush) and it still turns over and runs, and IS MAKING VACUUM at the MAP port (port F i believe). Tried the new AC/DELCO MAP sensor too. So it appears it is making vacuum, just not enough at start-up to keep the MAP sensor from flooding the engine. I am thinking it's a bad connection, maybe a bad ground or even a weak battery. Also, the MAP connector had been damaged (one of the pins). I think it was okay, but when I was looking for problems I suspected it was bad and cut it off, only to find that Chevy wants $31 for the pigtail (it's to the junkyard for me!). So it has been temporarily fixed with bullet connectors (ask me how...). Will try swapping batteries tonight. Sorry about the novel!

[armyBob]

I thought of something else. I had previously changed out most of the vacuum hoses. They were the old rigid plastic lines, and were very brittle with age. I used standard rubber hose, mainly 1/8" and 1/4" (which has a much larger I.D. than the old plastic hoses). Could this larger diameter be significantly affecting the vacuum signal to the MAP sensor? It was running fine with this setup before though...

[geoffinbc]

No hose diameter will not matter.

But seriously you honestly sound like you have a severe timing issue. Backfiring through the intake instantly points directly to timing and nothing else. I dont care if you think it is right GO CHECK IT.

Set number one cylinder at TDC COMPRESSION. Put you finger over the plug hole while someone turns the motor over and feel for a puff of air. Once you feel that, the cylinder is comming up the bore on its compression stroke. Now turn the motoruntil teh mark on the balancer is on the zero mark of the pointer.

Once this is established take a look at this picture http://members.shaw.ca/betterthanyou...nition2.8l.gif

Pay attension to where the front of the engine is marked. Verify everything is exactly as shown in the picture.

[armyBob]

Ok. Now that it runs should I just check timing while it's running, with the ESC disconnected? I hate doing it because the holddown bolt is very hard to get to - I have two heater lines (metal) running behind the dist along the firewall. Standard dist wrenches won't work so I take off the coil and EGR solenoid and use 1/4" drive ratchet with 1.5" extension. And I don't have an inductive timing light, just one with a spring (that #1 spark plug is buried, but I guess it could be worse i.e. transverse engine).

I double- and triple-checked the firing order and it's ok but I'll check again. Perhaps when I set the timing before there were other issues with the engine (not to mention a big fuel/possibly vacuum leak - why I rebuilt the TBI), and now the timing is off. I was told 10*BTDC, but it was pinging a bit at that setting. Maybe 8*? At this point I don't care as long as it runs! Thanks.

[geoffinbc]

Get an inductive light. It is worth it big time. 10* is spec and it shouldn't ping or you got some sad gas in that baby.

[armyBob]

Timing is dead on at 10*BTDC and doesn't jump very much.

But...in the process of troubleshooting I saw that one of the injectors was POURING fuel. Turns out the lower o-ring has a gash in it. It wasn't like this originally, must have happened while playing with getting this thing running. Spent all day Sunday looking for a replacement so I don't have to buy a rebuild kit again for one lousy o-ring. Finally found the old rings I had taken out, will coat with ATF and reassemble TBI tonight.

Also, I must have a bad ECM because the ground side of one of the injectors is spliced into the instrument panel fuse (it's grounded)! If I disconnect the splice that injector won't fire! I checked continuity from the injector pigtail back to the ECM and it's good, so maybe the ECM is bad, not connecting the injector to ground. The truck was running fine with this goofy setup, so I don't think this is the source of the trouble, but I want to fix it.

[geoffinbc]

Thats fucked. You should have 12V power from the ECMI fuse and then the 2 grounds goto the ECM. If an injector is POURING out fuel because it is constantly grounded then you would have massive over fueling.

http://members.shaw.ca/betterthanyoutoo/ecs2.jpg

[armyBob]

True, but it's the other injector that is leaking (with the bad o-ring). Strangely enough, the grounded one seems to be ok? The bad one sprays even with the harness disconnected. I hope to get it put back together tonight and see what happens. Then I can check for the grounding at the ECM and figure out why they did this hack job. I'm surprised it ran at all.