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1989 K5 350 TBI Fuel Issues?

All right..good news is at least it's running as good as it was.

Bad news is I have no idea what it was. I started this morning to get it warmed up. Idled and drove fine. None of the issues.

Here is what I checked.
1) o2 sensor looked relatively new. No concerns.
2) I replaced melted knock sensor wire. I think it is knock sensor. It is on the passenger side of engine block near manifold.
3) fuel pressure after fuel filter is 12psi.
4) was going to check timing but old and crusty engine doesn't have timing mark gauge on engine block. Not sure what to do.
5) engine to battery ground good.
6) the chassis was NOT grounded. It was disconnected. I grounded it.
7) I did not check compression since it was running ok again.


I'm guessing from good to bad and bad to good that quickly still a grounding issue.

Where does the ecm ground too?
 
Techson94 said:
All right..good news is at least it's running as good as it was.

Bad news is I have no idea what it was. I started this morning to get it warmed up. Idled and drove fine. None of the issues.

Here is what I checked.
1) o2 sensor looked relatively new. No concerns.
2) I replaced melted knock sensor wire. I think it is knock sensor. It is on the passenger side of engine block near manifold.
3) fuel pressure after fuel filter is 12psi.
4) was going to check timing but old and crusty engine doesn't have timing mark gauge on engine block. Not sure what to do.
5) engine to battery ground good.
6) the chassis was NOT grounded. It was disconnected. I grounded it.
7) I did not check compression since it was running ok again.


I'm guessing from good to bad and bad to good that quickly still a grounding issue.

Where does the ecm ground too?
Click to expand...

A faulty signal from the knock sensor can cause a lean situation also. The early electronic fuel injection is very limited on diagnostic capabilities. If the wire was melted on the manifold (single wire sensor) than it is only looking for a ground signal. If the ecm thinks timing is out because the knock sensor shows it via a short to ground, than it is possible to have the fuel cut back to compensate.

All three major grounds are essential also. Engine to frame, frame to body, body to engine. Wierd things happen sometimes if not. Also dont use the same 1/4" ground for everything. One of my first lessons on this in my career was a Detroit DDEC 2 engine (80s era) in an International seed truck that would randomly shut off driving. It would get towed into the shop. Once at the shop we couldn't find anything. One day it died for good while under the combine. In the middle of the field I figured out that the ECM had no power or ground. I ran some external wires to get everything started. Told the customer to empty the load and bring it to the shop. When I pulled the dash apart to diagnose further, I found a 1/4" bolt welded to the dash and every ground in the cab went to it. I started pulling one wire off at a time until the truck ran. I than found the AM radio was shorted out internally. Re wired new grounds and separated them. My point of the story, wiring is the culprit more times than the sensor. Sensors still fail, but check your wiring always.

Good Job and congratulations!
 
I read on another thread that ecm grounds to manifiold...

Second guessing what I read. Seams like it would ground to body in dash.

Any one know for sure?

Thanks again. For all input. Don't feel confident it is fixed because prior to any grounding I worked on it was running fine.

Doesn't matter cause I'm driving around today with top down!
 
If it's to a manifold it would be the intake manifold. There are some grounds back there IIRC, to one of the rrarmost intake to head bolts. Or to the back of the cylinder head. Of course doesn't really matter, as long as there is good contact.

If ECM ground was bad youd have a lot more issues, if it would even run. ECM grounds the injectors to fire them, for instance. Never hurts to check and confirm, I would just expect nothing to work if it were an issue. But poor connections can wreak havoc and be hard to pinpoint. I am all about assembly with dielectric grease.
 
dyeager535 said:
If it's to a manifold it would be the intake manifold. There are some grounds back there IIRC, to one of the rrarmost intake to head bolts. Or to the back of the cylinder head. Of course doesn't really matter, as long as there is good contact.

If ECM ground was bad youd have a lot more issues, if it would even run. ECM grounds the injectors to fire them, for instance. Never hurts to check and confirm, I would just expect nothing to work if it were an issue. But poor connections can wreak havoc and be hard to pinpoint. I am all about assembly with dielectric grease.
Click to expand...

Good point on the grease.
 
bassackwards said:
The first thing to do is replace EVERY sensor with a new quality sensor. You have to do this before going any further.
Click to expand...

Odd. I did that to mine when I first became a member here. The only plus side is I ended up with spare sensors. Found out the real problem was the EGR. And that was the most expensive part to replace at that time. :whistle:
 
Techson94 said:
Here is what I checked.
1) o2 sensor looked relatively new. No concerns.
2) I replaced melted knock sensor wire. I think it is knock sensor. It is on the passenger side of engine block near manifold.
3) fuel pressure after fuel filter is 12psi.
4) was going to check timing but old and crusty engine doesn't have timing mark gauge on engine block. Not sure what to do.
Click to expand...

As you get the issues worked out, you might want to get an AFR and bump up the fuel pressure. If going higher than 12psi is too much, you can drop it down. Either way you'll be able to adjust it.
 
Well I was rightfully concerned about me not fixing the problem.

Blazer left me stranded today. After an hour of driving...it started dying. Starts right back up...then when in gear give it gas dies. Definitely feels like it's losing spark not gas. I tested fuel pump yeasterday and has 12psi.

Ignition module would be first guess? Grounds are good.
 
Fuel and spark, both pretty easy to at least do a rudimentary test. Not a typical ignition failure mode to be able to restart and idle.
 
So, I have a truly random failure that is pretty similar. Do you have a CEL coming on when it dies? Battery disconnect to make sure you clear codes.

We did about 350 miles with 2 K5s and my Suburban. One of the K5s kept dying with no codes. It would start right up though. We were about 2 miles from my place when the group was gonna split up. The second K5 and myself turned off to go to my place. The K5 that kept dying never left the stop light. It finally failed and had to be towed to my place. We found the ground wire at the fuel pump was corroded and broken. It had been causing the TBI to randomly lose fuel pressure.

Can you leave a fuel pressure gauge hooked up inline? Drive for a bit and see what you get.
 
Well I was putting a used engine in my truck and the ecm harness looked old and crusty so I bought a new one from the dealer.
Couldn't start the engine.
Started changing sensors until I changed all and still no start.
The engine was running before it was pulled so we checked the harness and found no power to the injector.
Traced the power and it was all good going to the ecm.
Finally after a week of this we checked the pin out on the new harness and found 2 wires were swapped in position.
Just changing all these parts to have a better condition was the dumbest thing I ever did.
Now I leave well enough alone and if I have a problem I can find it.
 
Just in case it wasn't clear, the new harness from the dealer was manufactured wrong.
Cost me a week of no work and one week of the shop time
 
SOLVED.

I thought I would let everyone know. I think it was pick up coil. I bought a spectra premium distributor with all new electronics for $75 amazon.

I chickened out and paid the mechanic $94 to install it.

Runs better than it has since I bought it. Drove it for several hours and no problems with idle, bogging, or cutting out suddenly.

This forum is awesome. Thanks for all your advice.
 
Glad you figured it out. I've had mixed success with spectra distributors. One has lasted 3 years in my 350 tbi. The one in my 454 tbi in on its third in 2 years. I now have delphis in both.
 
thearborbarber said:
Glad you figured it out. I've had mixed success with spectra distributors. One has lasted 3 years in my 350 tbi. The one in my 454 tbi in on its third in 2 years. I now have delphis in both.
Click to expand...

I was not excited about it. But just need a year until I save for the 5.7 vortec or 6.0 ls.
 
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