C4ProjectCar

I just bought a 1990 C4. After a little electrical work, I managed to get it running. However, it has a few issues I can't resolve. Namely:
- Hard to start when warm; it seems like it's flooded. I have to hold down the gas, then feather it once it starts.
- Low oil pressure when warm. When it is warm, it loses almost all oil pressure, which it seems to do only at idle.
- Chugging when warm. After I drive it for a few minutes it starts chugging badly and seems to lose nearly all power, even when in neutral.
Here's some relevant information:
- It has a new HEI distributor, new spark plugs and wires, and new injectors.
- The previous owner recently had the oil changed to 5w-30 synthetic.
- The previous owner said the problem with the low oil pressure started when he recently had new fuel injectors put in.

Do these symptoms point toward any specific problem?

DinoBob

Stop running that car until you figure out whether the injectors are stuck. If you ave a bad injector you could be filling the crankcase with gasoline. You'll ruin something for sure. Check the oil. Smell it and see if the level is high.

playsdixie

running that bad and no codes?..
if not, start with the basics....make sure timing/tpi is set/min idle adjustment....pull the vac line on your pressure reg and look/smell for gas...spray tb cleaner around the vac lines to look for vac leaks....

C4ProjectCar

I remember the oil does seem high, but I'm not sure if it smells like gasoline. That's what I should smell for, I assume?
Is that the best way to see if an injector is stuck?
No check engine light, but that doesn't necessarily mean no codes, right?

playsdixie

I have an 85...to read the codes, I jump a and b on the aldl. count the flashes....if you smell gas around the fpr, with the vac line off, that's a problem....if you have codes, record them and then disconnect the neg battery to clear them to see if any come back...

if you don't have a factory fsm, I strongly suggest you get one...and a pressure guage for the fuel rail.....it sure will help with troubleshooting.

agiain, I would check the timing/tps first.....assuming you have proper fuel pressure...

C4ProjectCar

I'll check if there are codes. I'd rather not run it to check for gas around the FPR, though, in case an injector is stuck.
Where would I get a factory service manual? I have the Haynes manual for it.
I have a fuel pressure tester, so I'll check that.
The previous owner recently had it tuned up, so the timing should be good, but I'll check the TPS (throttle position sensor, right?).

fredd1

You might want to try 10w50 for your oil pressure issue. The chugging, stalling problem sounds like a failing fuel pump. You'll need to check the fuel pressure at the rail. S/B around 40-45psi IIRC. I'd also change the fuel filter and as someone else suggested check for a leaky pressure regulator diaphram.

C4ProjectCar

Would heavier oil really fix it though? It seems like a patch for the symptom, not the problem.
I just bought a new fuel filter, and I plan to replace it today.
I floored the gas and turned over the engine, which per the owner's manual should close the injectors, but as I held the key it sounded like it was beginning to start. I could also smell gas coming out of the exhaust. This seems to me like it indicates a stuck injector, right?

playsdixie

a stuck injector isn't going to interfere with a test to see if it's your fpr...you should be able to see relatively quickly whether or not the regulator is bad....you'lll smell gas.....you can get a factory gm manual on e bay....haven't seen a lot of threads regarding stuck injectors, so not really sure that will turn out to be your problem....\
with guage hooked up, turn on key...don't start....pressure should be up in 2 seconds...then pump shuts off...check pressure when running to see if it stays up....start with the basics or you're be changing parts til the cows come home ...paul

C4ProjectCar

I'll do that as soon as I get my new fuel filter on.
I poured out the dirty gas from the old one, and saw lots of fine metal particles in it. Is that a sign of a worn fuel pump?

fredd1

Heavier oil may help but if your main bearings are shot, probably not for long. Also, as suggested check the fuel pressure. If it stays high for an appreciable amount of time after you turn off the key your PR diaphram probably is ok. Check the PR vacuum line for leaks. Running rich could also be bad readings from the tps, coolant temp. sensor, etc. Lots to check before assuming a stuck injector.

C4ProjectCar

I attached the pressure gauge, turned the key to on, and the pressure only went up to about 4 PSI then went back down. Even with cycling the key on and off I only got it to about 9.
Now it won't even start for more than 1/2 of a second.

C4ProjectCar

A local mechanic who happens to be a Corvette enthusiast told me it's the fuel pump, given the low pressure and the metal in the fuel filter. Since it is an easy repair and only $70, I'm probably going to go ahead and replace it.

playsdixie

i'd check around for pumps there are several upgrades....chances are the whole sending unit is nasty by now....corvette central has a nice stainless unit...easy to install...get the pump you want...most like the walbro 255

C4ProjectCar

Honestly, I don't want to have to wait for something online, and since I don't know for sure the fuel pump is the problem, I'd rather go with something cheap.
Do you see anything wrong with this one?
http://www.oreillyauto.com/site/c/de...0401&ppt=C0025

C4ProjectCar

Plot twist:
I removed the pump, looked in the tank, and I'm out of gas! Guess that's why it wouldn't start and had no fuel pressure. The gauge showed 1/2 of a tank, so I must have a bad sender in the tank.

playsdixie

get the stainless unit and pump corvette central has...real nice unit...not expensive...

C4ProjectCar

My impatience got the best of me and I bought a pump at O'Reilly Auto Parts. Long story short, the pump was shorter but the wires that came with it weren't longer, so I ended up exchanging it for a different pump they had. Hopefully the new pump will solve some of my problems.

C4ProjectCar

Fuel pump in; it runs fine. In the few minutes I had it running, oil pressure stayed at 60 PSI, leading me to believe that sender is not functioning properly. I've heard it should have 10 PSI for every 1000 RPMs, meaning at idle it should have about 9 PSI, not 60. Come to think of it, I don't think I've seen it anyplace other than 60 PSI, or near 0.
Fuel pressure was only about 42, which seems a little low. Also, with the key on but engine off, it lost pressure fairly rapidly - about 1 PSI every 2 seconds. Tonight I'm checking if the fuel pressure sensor vacuum hose smells like gas (with the engine off, I assume?) and checking for vacuum leaks.

lt4obsesses

Maybe someone will chime in on how to check the oil pressure mechanically. I know mine reads low at idle warm and moves up with rpm. You may have a failing sending unit.

42 psi on fuel is good. As far as it dropping quickly, that could be the fpr, or a leaking injector.