tonys91rs

iTrader: (17)

i have a 92 s/d tpi converted onto my 305. simple plug and play and runs great until recently.

after sitting a few days, it has difficulty starting. it cranks but sometimes wont turn over. then i have to jump it. at other times, it acts like its hesitating or starving for gas , then runs fine after it runs a few moments.

the pump is new and i hear it priming. pressure is at 40. no ses lights or codes. clean plugs and wires. on a stethescope, the injectors are running.

the fuel regulator and injectors are original. im guessing it may be dirty or worn injectors, or regulator. anyone with an idea?

ASE doc

Could be a leaking regulator bleeding off pressure. Also, very likely an issue in the tank. There is a pulsator in the tank(plastic housing with rubber seals inside that seal tbetween the pump and the sending unit). These commonly fail and bleed pressure causing the pump work extra hard and also cause a loss of prime.

The test to determine where the pressure loss is in the system is to connect a fuel pressure gauge and start the engine to bring the fuel pressure up to spec(40-45psi). Then, pinch off the return line and watch for the pressure to go as high as 80 or 100psi, quickly shut off the engine and watch the fuel pressure. If the leak is at the regulator the pressure will hold steady or drop very slowly with the return line pinched shut. If the leak is in the tank, the pressure will continue to drop off even with the return line shut. Have a helper start the engine and shut it off. Just as the engine stops, before the fuel pressure drops off, pinch the supply line shut. If the leak is in the tank, the pressure will hold with the supply line shut. If the pressure bleeds off with both lines pinched shut, the leak is at an injector or the regulator diaphram may be ruptured. Remove the vacuum line from the regulator and look for fuel coming from the vacuum port. If the regulator is okay, you have a leaking injector.

If the fuel pressure holds with no lines pinched off, you have a cold start fueling issue which is most likely caused by poor injector performance. It may also be due to a defective ECT sensor or ignition tune.

tonys91rs

iTrader: (17)

very informative and interesting. i did notice when the pressure gauge is connected on the intake that it holds pressure around 40 for quite a while. once its started and running, it will start without issue afterwards until its been a day or more.

ill follow through your suggestions.

ASE doc

It's normal for fuel pressure to bleed off over a period of several hours. Normally, the pump would recharge the system quickly, starting with the prime, then reaching full system pressure right away once cranking starts. If there is some issue causing the pump to be slow to make pressure, perhaps a restricted filter, it may be causing the pressure to come up too slowly. If pressure holds for several minutes, it's unlikely that there is a pressure leak large enough to cause an issue.

Other things that will cause hard starting would be low KV from the coil. You might try testing this with an adjustable spark tester. An engine scope would be even better. 92 doesn't have the cold start injector so that wouldn't be an issue.

It's possible that your ECT sensor may be slightly off. I diagnosed a Volvo hard start yesterday. The ECT on datastream was 78 degrees, IAT was 80 degrees. This was after the engine had just been running. My laser thermometer showed actual coolant temp to be 150. This was a huge error in coolant temp and caused the engine to run very rich, causing a hard start and rough idle after starting. However, since the sensor was not out of range(-38 or 280) there was no DTC set.

From your description, I would be looking for your ECT to read higher than actual, causing the cranking and after start enrichment to run on the lean side. You can use a laser thermometer and a scan tool to verify this.