1985 C4 warm starting problem
Thread Starter
Intermediate
Joined: Jul 2012
Posts: 25
Likes: 0
1985 C4 warm starting problem
My 85' C4 auto has a warm starting issue. Last summer I had all the injectors refurbished by FIC, including the cold start injector. It has ran fabulously since then. When cold, it starts on the first turn of the starter. When warm it requires a lot of cranking occasionally and sometimes requires depressing the throttle down. It would appear that engine temperature when starting is the issue that is effecting the starting. I do hear the fuel pump spin up prior to cranking the engine. There are no trouble codes stored. I have searched the C4 forum and did not find a similar post and would appreciate any help
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Your CTS (Coolant Temperature Sensor) on the front of the intake manifold under the throttle body could be bad. It tells the ECM what the coolant temperature is and if the ECM thinks the coolant is cold it will run rich. If the connector is not making good contact or the wires are broken the ECM will see low temperature.
The CTS is pretty cheap at any auto parts store, so it's easy to just replace it and see what happens.
The CTS is pretty cheap at any auto parts store, so it's easy to just replace it and see what happens.
Thread Starter
Intermediate
Joined: Jul 2012
Posts: 25
Likes: 0
I'll try it!
Your CTS (Coolant Temperature Sensor) on the front of the intake manifold under the throttle body could be bad. It tells the ECM what the coolant temperature is and if the ECM thinks the coolant is cold it will run rich. If the connector is not making good contact or the wires are broken the ECM will see low temperature.
The CTS is pretty cheap at any auto parts store, so it's easy to just replace it and see what happens.
The CTS is pretty cheap at any auto parts store, so it's easy to just replace it and see what happens.
Maybe I'll should do both at the same time?
Thread Starter
Intermediate
Joined: Jul 2012
Posts: 25
Likes: 0
Found I had two problems, no three!
First I thought I had a cold start valve issue, so I sent the cold start valve along with all 8 injector to FIC for a refurbishment, flow and leak tests. FIC told me they were performing perfectly now and did not need replacement. Along with a fuel filter and a tune-up of plugs, cap, rotor and wires it ran like it was supercharged. Performance and throttle response is spectacular.
I still would have starting issues particularly when warm. Cleaned the MAF sensor and throttle body and I replaced some inexpensive sensors: coolant temperature and O2. The fuel pressure would build to 40 psi then quickly drop within a minute or two to 6 psi. When running it would maintain about 39 psi. To further test the fuel pump and isolate the leak I needed to find the fuel pump lines where they could be pinched off.
Got great help from the a forum member. To access the fuel pressure and return lines, you remove the gas tank lid and the panel under it which exposes the filler neck and fuel pump mounting panel. The top hose on the right with two hose clamps is the supply and the lower right hose is the return.
It was obvious that the fuel regulator was not leaking into the vacuum line, because when the vacuum line was removed and the system pressurized no fuel leaked out of the vacuum fitting on the regulator. (So I thought)
Pressurized system and clamped supply hose above the tank and pressure held so no leaking injectors or cold start valve.. Removed clamp pressure dropped immediately indicating bad fuel pump.
Replaced the fuel pump. Very simple to do by removing 8 bolts around filler neck and entire unit just lifts right out. Installed new pump in minutes. Also replaced the strainer and fuel filter. The system now holds pressure after cycling.
This solved my problems. I thought!
Then after the system was now holding pressure, it started great but after a long period it was again requiring a long crank, but restarting after a short period no problem. Now I smelled a slight gas odor under the hood. When I removed the fuel pressure regulator vacuum line I found it wet with gas and gas now weeping out of the regulator. It was not obvious and did not occur previously after removing the vacuum line, because the pressure would bleed back faster through the fuel pump.
The now 40 psi static pressure, that was now holding after shut-down, was very slowly bleeding gas past the regulator diaphragm into the vacuum line and allowed it to be be sucked down the vacuum line into the plenum. Since my primary pressure loss was from the bad fuel pump, it masked the slow leaking fuel pressure regulator diaphragm.
Order a new diaphram from FIC and replaced the leaky diaphragm. Now it starts great, now the idle was very low and would stall occasionally. All that leaking fuel was causing a rich condition at idle, compensating for a bad AIC valve. Installed a new AIC valve and now it runs and idles perfectly.
I am very confident that multiple issues and some failures were compensating for each other that were contributing to my starting problem.
I still would have starting issues particularly when warm. Cleaned the MAF sensor and throttle body and I replaced some inexpensive sensors: coolant temperature and O2. The fuel pressure would build to 40 psi then quickly drop within a minute or two to 6 psi. When running it would maintain about 39 psi. To further test the fuel pump and isolate the leak I needed to find the fuel pump lines where they could be pinched off.
Got great help from the a forum member. To access the fuel pressure and return lines, you remove the gas tank lid and the panel under it which exposes the filler neck and fuel pump mounting panel. The top hose on the right with two hose clamps is the supply and the lower right hose is the return.
It was obvious that the fuel regulator was not leaking into the vacuum line, because when the vacuum line was removed and the system pressurized no fuel leaked out of the vacuum fitting on the regulator. (So I thought)
Pressurized system and clamped supply hose above the tank and pressure held so no leaking injectors or cold start valve.. Removed clamp pressure dropped immediately indicating bad fuel pump.
Replaced the fuel pump. Very simple to do by removing 8 bolts around filler neck and entire unit just lifts right out. Installed new pump in minutes. Also replaced the strainer and fuel filter. The system now holds pressure after cycling.
This solved my problems. I thought!
Then after the system was now holding pressure, it started great but after a long period it was again requiring a long crank, but restarting after a short period no problem. Now I smelled a slight gas odor under the hood. When I removed the fuel pressure regulator vacuum line I found it wet with gas and gas now weeping out of the regulator. It was not obvious and did not occur previously after removing the vacuum line, because the pressure would bleed back faster through the fuel pump.
The now 40 psi static pressure, that was now holding after shut-down, was very slowly bleeding gas past the regulator diaphragm into the vacuum line and allowed it to be be sucked down the vacuum line into the plenum. Since my primary pressure loss was from the bad fuel pump, it masked the slow leaking fuel pressure regulator diaphragm.
Order a new diaphram from FIC and replaced the leaky diaphragm. Now it starts great, now the idle was very low and would stall occasionally. All that leaking fuel was causing a rich condition at idle, compensating for a bad AIC valve. Installed a new AIC valve and now it runs and idles perfectly.
I am very confident that multiple issues and some failures were compensating for each other that were contributing to my starting problem.
Last edited by edobernig; Jul 14, 2013 at 08:33 AM.
