Hey Guys,

My 305 TPI just began acting up. I've had to open the throttle just to keep it running...now it won't start at all unless I hold it at full throttle.

What I've observed:
- VERY wet and gas-smell plugs...all of them
- Fuel pressure is 40+ psi when the ignition is turned ON, and sometimes immediately falls to 0 psi, making gurgling noises (stays 40 psi during crank)
- No leaking fuel anywhere (engine is on a test stand, so everything is visible)
- Fuel pressure regulator replaced a few months ago
- Injectors professionally cleaned a few months ago (Cruzin Performance)

This is strange...
I went to the shop this evening, changed the spark plugs and it fired right up...sounded great and revved really well. In short time it stumbled and stalled...and won't start again. The new plugs are wet.

Any ideas??

 

check your EGR valve. Had the egr stick open on my S10 Blazer (MPFI 4.3) one time and it did the same thing. Ran okay above 2500 rpm but would begin to miss as you let off on the gas, and would not idle. plugs were wet with gas, changed plugs and got the same thing. Got the egr valve working right and it straightened right up. Sometimes a piece of carbon can hang the valve open.

 

possibly one fuel injector is bad. Ohm out the injectors and tell us what the reading is ....

 

Is the TPI MAF or MAP? It may make a difference.

Also, even though Rich does excellent work, and you injectors probably came back as good as or better than new, that doesn't prevent contaminants from entering the cleaned injectors and fouling them. Your description of the symptoms, and the fact that the fuel pressure is dropping almost immediately after the pump shuts off might be leaking injectors.

 

I myself bought a pulse tester . Just to find out the my injectors ohmed out okay . But they would bind under load. Great tool to buy

 

Wow, thanks for the responses. I'll get a chance to try your ideas this weekend.

Vader,
I build a lot of speed density harnesses, so it's been a few weeks since I built a MAF harness. I have one on my harness template right now that should be done on Friday. Just for the heck of it, I'll throw the MAF harness on the test engine and see if I get the same results.

 

I installed a MAF harness I just built and after a few cranks/stalls (and dark smoke) it fired up and ran great. So..... that means something is wrong with the speed density ECM or memcal. I'll find out soon enough...I have plenty ECMs and memcals to work with.

Here's what's happening with the speed density electronics. When the ignition is turned ON, the fuel rails are pressurized, then I hear some sort of sporatic ticking (not quite like the IAC motor) and the fuel pressure drops to zero. I knew that rail mounted pressure gauge would come in handy. For some reason the ECM is opening the injectors when the engine is not running, dumping fuel, and soaking the spark plugs. When the key is turned OFF and back ON again, the injectors don't necessarily immediately open...it's unpredictable, however they eventually open without the engine running and fuel pressure goes to zero. I've played with TPI systems for more than 5 years and never seen something like this. Now that I think about it, I think the ECM I was using was a used one I just received last week.

After the MAF harness was installed, the engine started/stumbled/stalled about 5 times, throwing dark smoke out the exhaust before the extra fuel was burned to get the engine running right. This occured because I was troubleshooting the problem with the speed density harness just an hour prior.

Before I find out if the problem is the speed density ECM or memcal, anyone want to take a guess?

 

I'll guess V6 memcal
Fueling code is different on the 6's, could be almost double from what I recall.
Could also be in factory test mode causing all outputs to cycle (clicking). Not sure if that has injector effect or not.

 

I'm using a V8 memcal. However, I suspect this memcal was a culprit in the mysterious stalling in the 1986 K10 TPI swap we did last fall. After the memcal was replaced, the sporatic stalling stopped. I could never get the memcal to consistently act up.

Here's the 86 K10 TPI swap: http://www.eficonnection.com/eficonn...10/default.asp