GMC Van..Hard starter warm, even harder cold

[Rollerjim]

1990 GMC 3/4 ton 350 engine floods every time I start it warm or cold then after the excess gas clears out it runs OK until I shut it off and have to start it again. For a couple minutes after I start it, I get black or blue smoke out the exhaust, backfiring, stalls, and rough running in general. If I unplug one of the two injectors, it smooths out somewhat. Sometimes when cold it doesn't even start and I have to take out a few spark plugs and clean them up. They are all wet and black. #8 is the most soaked. When I crank with it out, the gas pours out.

This started happening after I put a '91 engine in it. I don't suspect the fuel pump or filter because it handled the old engine quite well before I blew it up. I strongly suspect the problem is due to something I (not an expert) screwed up while doing the engine switch. What could it be though? I had to put the throttle body from the old engine on the new because my linkage wouldn't work on it. What could I have scewed up there? I put new plugs in it gapped at .035 like the parts salesman said and plug wires. I tried putting several parts from the old engine in the new....dist.cap, rotor, coil, O2 sensor. The EGR valve on the new was shot. It ran much better when I removed the vac hose from it, so I put the one from the old engine on it.

I'm guessing fuel is getting into the intake manifold after I shut it off, but I don't see any leaking down from the injectors when I shut it off. Is there somewhere else that fuel can leak in other than the injectors? I switched injectors from the old to new and back again, plus injectors from another TBU I had...no help. no difference.

I don't have anything to look for codes with and I don't know where the ECM is anyhow. The SES light stays on all the time though. I don't know if it's because of the flooding or something else.

Any ideas, anybody? I'm all out of them!

Jim

[bduff509]

Maybe your coil is getting weak. Look into some new wires, cap, rotor. Check your connections for dirt & corrosion at the coil.Try flooring it just after you start cranking. That should stop it from flooding. You can bring the codes up by jumping the 2 terminals in the upper right-hand corner of the black connector just under the dash below the steering wheel (that's where it is on my Safari). A paperclip will do. Turn the key on. DO NOT start the engine. You should get 3 sets of flashes per code, the first being 12 ( 1 flash, break, 2 flashes, longer break)on your SES light. The 12 means the computer is working. A 43 would be 4 flashes, break, 3 flashes, longer break. Record what you get. After you get all of the codes it starts over with 12 again. Now all you have to do is find out what they mean. Your local GM dealer can tell you that. Not all codes stay in memory after you shut off your engine. Some can only be gotten while the engine is running under a fault condition. To clear the codes just pull the neg. wire off of the batt. for 10-15 sec. You should do that after you retrieve the codes so you don't get old info the next time you try to bring the up. Good luck.

[Rollerjim]

Hey that's a pretty nifty! I didn't know you could do that! I followed your instructions and it works. There is a ckicking noise from the injectors when I jumped the terminals...I hope that's normal. I pulled a 15, 33, and a 45. I found a code site on the net http://www.troublecodes.net/GM/89-90_57k.shtml and here's the explanations...

15 Coolant temperature sensor signal indicates a temperature colder than -27° F for 30 seconds after the engine has been running for at least 30 seconds.

33 MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 4%.

45 Oxygen sensor voltage was over 0.7 volts for 30 seconds of closed loop operation with a throttle angle between 2% and 20%.(Rich Exhaust Indicated)

I cleared the codes in case they were old, started it back up blowing soot all over anything in my garage that was in the line of fire of my tailpipe, shut it off and checked again. This time I only got the 33. Problem is I don't know what to do about it. Could it mean a bad MAP sensor? The guy at the parts store said 60 bucks for a new one and I can't be sure it's the problem or maybe a vacuum leak or something else. I don't even know which sensor it is. Is it the one with 4 wires (all with green in them) that screws into the passenger side of the throttle body or the one with 3 wires at the rear of the engine?

I replaced the ignition coil with one off my old engine and no change.

Thank you for your much appreciated help!

Jim

[bduff509]

You're quite welcome. I never took notice whether my injectors clicked or not. I'm not sure what's up with the MAP sensor. Are you sure that you don't have a bad vacuum leak? I don't know a lot about newer vehicles. Only what I've picked up along the way. My '94 Safari is the only vehicle I've ever owned newer than '81. I've learned a lot from it in 10 yrs. Your best bet would be to go to GMC or Chevy non-specific & post a new thread with that question. There are a lot of pretty sharp people on this site. The only down side is you may have to sort through the info for the best advice. I haven't seen too many people being steered wrong here though. The alternative is to buy a Haines or Chilton manual on your vehicle, which you should probably do anyway. They're normally pretty good but don't always tell you everything you want to know. Thanks for the link. It'll come in handy.