93 gmc 3/4 van 5.7 tbi cold start problem

[marcia]

Hope you guys can offer some suggestions as to where to start.
Engines crank speed fine but takes about 20 seconds to start when cold. And by cold I mean engine cold not weather. Then wants to stall and will do so if you try and pull out of driveway. Feels like an unchoked engine but this has no choke setting ability. Have to wait til starts to get warm before the problem goes away. Once up to maybe 110 degrees on the gauge trouble is gone.

Have considered fuel pump pressure, but why would that be a factor if once warm runs like normal(great). Fuel filter is pretty new. Plugs brand new and made no difference, timing is right on. Don't know what to look at next. No check engine light on after startup but does work on start. Never comes on while driving as it did once when o2 sensor went balistic....boy did she run good then. too bad we had to replace it..lol

fuel filter changed about 4 months ago.
No trouble codes set.

any suggestions would be greatly appreciated.

[GasGuzzler]

TBI's are sensitive and it takes someone from a bygone era to help. I do know that the grounds for the computer are really important. Not sure about a van, but the trucks have a braided strap on the passenger side of the firewall that links the body, engine, and frame. They all need to be in good order. Also, make sure all of the grounds at the tstat housing are not on the same stud. Keep them on different studs when possible.

You have the classic symptoms of a lean TBI system. The reason fuel pressure is so important on this engine is two fold. One is that they run only 9-13 psi of pressure....so it's possible the pressure is down a little over time...doesn't take much to get out of spec. Two, there are only two injectors to distribute fuel.

Because a cold engine needs more fuel than a warm one (hence a choke mentioned on earlier vehicles), the fuel system needs a complete once over.

There is no pressure tap for these....you'll have to remove the filter and install a pressure gauge adapter in its place. Make sure it's 9-13 psi, preferably 11+.

Use a timing light hooked up to the coil wire (instead of the #1 plug wire) with the engine running to look at the injector spray. You want to make sure both are spraying a good, fine pattern. Also make sure the regulator is not leaking (behind the injector pods).

These engines also have problems inside the distributor although it doesn't sound like your problem. Measure the resistance of the pick up coil inside. I think it's supposed to be 900 Ohms but I pretty much just pulled that out of my a$$. I'll look it up if needed.

Also, the magnet in the middle of the reluctor inside the distributor (part of the shaft) will crack over time, thowing off the operation of the pick up coil. Make sure the cap, rotor, wires, and coil are in good shape with no corrosion.

Like I said before, igniton system problems on this engine usually show up in poor performance, stalling, and misfiring with the engine HOT.

You also need to check really close for vacuum leaks. A vacuum leak on this type engine will also obviously cause a lean condition and when cold, will be a handlful to keep running. Remember, with no MAF, a leak has to be pretty damm big for the idle to be too high.

[marcia]

Guzzler, thanks for the suggestions. One ? on the injector test for spray. How do you see the spray pattern, looking down into the tbi? Sorry if this is a stupid ? Hubby is the mechanic...lol
thanks again for the help.

[RedHeartbeat]

I'd put in a new ignition module in the distributor if I were shooting blindly.

[GasGuzzler]

Yes, the timing light will blink every time the injectors pulse if it's hooked up to the coil wire. The light is bright and helps show the pattern. Shine it down into the top of the throttle body with the engine running. Without the light, the stream will look steady. With the light, you'll be able to see the pulses of fuel.

[marcia]

thanks guys, will pass these suggestions on and let you know what we find. I guessed right on the injector business, guess after 45 years with a shade tree mechanic something rubbed off...lol
thanks again