Intermittent hard start with dieseling

Mumaw

Member
96 K3500 chevy, 454 has an intermittent hard starting problem. Usually the truck starts on the first crank. Every several days or couple of weeks it takes 5 to 7, 10 sec. cranks before starting. Between cranks, the engine diesels but has not yet started. Then it starts. No problem starting the rest of the day or several days after. No codes show on scanner. The truck runs fine with normal performance. Replaced crankshaft sensor, fuel regulator, fuel filter. Fuel pressure is a steady 55. I haven't found anyone who has heard of dieseling while cranking. What is the problem? Intermittent problems are so hard to solve.
 

nana1962409

Well Known Member
Supporting Member 2
My 97 k3500 was acting similar to that before I parted it out. In my case it was the temp sensor for the ecm. The sensor was leaking slightly internally and corroded the connector and sensor pins. I replaced the sensor and pigtail and the problem was solved in my case.
 

MRHP

 
Supporting Member 1
If you run it for 1/2 hour, then let is sit for 15 minutes how does it start. Those vortec 454 engines are prone to leaking injectors. Quite common.
 

Mumaw

Member
Once I start the truck , it has never failed to start easily on first crank the rest of the day, and runs well.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Put a fuel pressure gauge on it and see how long it takes to make pressure,the fuel pump could be going. Get a scan tool,set it up for the coolant temp.Do this when the engine is cold and the hard starting is occuring.The temp sensor should read pretty close to the out side temprature.If it's reading high,like 120--130 degrees that coolant sensor is lying to the computer.
 

409newby

Well Known Member
Supporting Member 11
Not a Chevy but I had a Ford years ago and the high pressure fuel pump would only pump when it felt like it, replaced pump, fixed the problem
 

Mumaw

Member
I think my truck is being deliberately elusive. Twice I put the fuel gauge on it after it did not start, checked pressure, and it started immediately after started so I still don't know for sure about pressure when it does not start.
When I checked the pressure, I turned on the key ( not cranking) the pressure was 52 psi immediately, fell to 48 psi in 2 minutes. I turned off the switch and back on after a min wait and pressure went to 55 psi. Checked pressure while running at 55.

I have had this truck 5 years. Only 25,000 miles when I bought it. Apparently had been sitting for quite a time. I replaced the fuel pump then and it started and ran great until now. It has 50,000 miles now. The last 2 months this nonstarting has gotten progressively more frequent. At first it would start after some cranking and dieseling. Now some days it will not start until the next morning or days later. Of course it always starts when the mechanic comes to check it!

I have been hoping the unique aspect of dieseling while cranking would lead to a solution.
Thanks for the interest and comments
 

Don Jacks

Well Seasoned Member
Supporting Member 3
A lying sensor will make the computer think that the engine is warmer than it is making the engine's mixture lean which could be the cause of the "dieseling".It's not far enough off to cause a check engine light . I've also seen them get off the other way and flood the heck out of a fully warmed up engine.I think that your fuel pump's ok.
 

Mumaw

Member
Oldskydog I will check tomorrow on the relay. It would seem to me that if the fuel pressure always is correct that a faulty relay is unlikely but I don't know much! Thanks for your suggestion .
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Well if you check the service manual there's an ohms to temp chart that can be helpful.Trick; when the truck is in it's failure mode,unhhook the sensor and see if the truck will start.If it does don't let it run long because an open in that circuit causes the ECM to cooommand dead rich[-40 C].If you're going to do your own work on this truck you need to invest in a scan tool,not just a code reader but an actual tool.It will once you learn how to use it,save you considerable money.
 

MRHP

 
Supporting Member 1
Check the cap and rotor. Known to corrode badly. Also the center shaft of the distributor has a flexible magnet compressed by a reluctant wheel. If the magnet or reluctor wheel have cracks in them, it can cause all kinds of starting and drivability issues. You could get the distributor shaft from G.M. years ago. Not sure about now. Or you could replace the complete distributor. Make sure to retime engine per the service manual.
 

Mumaw

Member
For some unknown reason the gear on the distributor shaft sheared off. So about 15,000 miles ago I replaced the distributer shaft, cap and rotor. No problem since.
 
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