TheCob

It's a 91 RS 305 TBI. Long Story, but essentially it has been sitting for 7ish years. At one point (roughly 5-6 years ago) about 2 gallons of diesel was accidentally added to about 2-3 gallons of year old gas in the tank. Someone put diesel in the regular gas can and didn't tell me. Fast forward to today. All the fuel has evaporated, some was drained then the rest evaporated.

I have done the following:
new battery
new fuel pump
new fuel filter
oil change
disassembled, cleaned, reassembled TB
Checked plugs, look good, only have less than 10k since last full tune up.
New gas

With some starter fluid in the TB it fired right up. Once the starter fluid burned off it started idling really rough, but not to the point that it died. After maybe 2 mins it returned to a normal smooth idle.

Drove it for 2 or 3 days, maybe a total of 50 miles, ran perfect. Went to start it after sitting overnight and it didn't want to fire. Gave it some gas and it reluctantly fired up, but wouldn't stay at idle, had to gas it to about 2500 rpm. After a minute or 2 of that, it smoothed out and ran normal.

Over the next 2 days it got progressively harder to start using the above method, with one caveat; it turns over, runs, and idles fine once it is warmed up. For example warmed it up and drove to the gas station. I went to put more gas in and I was nervous about being stranded at the station, but after fueling, got in and fired up as if it were new.

After sitting over the weekend I tried to start it Monday and it did the same thing, but this time there was a lot of black smoke and smelled like carbon. Same thing again, gassed it to 2500 -3000 till it smoothed out and drove it around the block. Shut it off, then as a test started it again and it ran fine.

I decided that I should run seafoam through it to try to clean out any gunk. I ran about 6 oz through the vac at the brake booster, about another 6 oz in the crankcase, and the rest in the gas tank with about 5 gallons of fresh gas. After letting it set for about 20-30 mins, fired right up and had quite a smoke show. Drove it for maybe another 20 highway miles, putting it through its paces and it ran excellent.

Parked it overnight, went to start it this morning and same thing, gassed it till it smoothed out and drove it 10 miles to work. I also noticed black flaky stuff on the driveway under the exhaust if that is relevant.

Any ideas of why it wont start up cold?

Bob88GTA

iTrader: (2)

Carb sounds a tad gunked up. remove it and clean it all good. Probably got some blocked passages/orifices. Check your vacuum lines for rot and relpace

dmccain

iTrader: (2)

After setting up that long there are tons of stuff to be checked. You've already done a lot. Id go ahead and change what sensors I could,o2, IAC, etc.. I may would check my fuel vent lines or pretty much any line that could be dryrotted etc..Intake gasket should be changed. Engine must be healthy so that's a good thing it may smoke for now on but that may not bother you too bad. My car puffs a huge cloud after sitting a few days that's because its old and didn't get as much use as it should have for many years. Doesn't bother me. Hang in there you will get it right and good luck with it.

Thomas_Simon

I just fired up my 1986 350 Z28 after about 6 years of sitting. It fired up fine after changing the battery and putting some fuel in the carb but had a leak in the fuel pump line. It was in a tight spot and I could'nt jack it up to get under it and look around. Had fuel squirting about 6 feet in the air lol. I will be able to move it and take a look at the hoses today. Thanks for posting thios as it gives me a better idea of what to do to a car sitting soo long. Good luck with your starting issue.

novaderrik

check the wiring to the temp sender in the intake manifold. if the wiring looks good, then try a new sensor. that's cheap and easy..

92RS_Ttop

iTrader: (3)

Check your fuel injectors, lines, and regulator. It sounds like your fuel pressure is bleeding off after it sits for a while. Connect a pressure gauge to the fuel supply line right behind the TBI unit. Get the car started and wait till it idles good, then take a reading off the gauge. Should be around 12-14 psi if it's the same as my old TBI Chevy truck. Shut the engine off and take another reading after a minute or so. Walk away for an hour or 2. Come back and check the pressure reading WITHOUT cranking the engine or even turning the key "on". It should read within 1–2 psi of your previous reading. If not, you have a leak somewhere that is letting pressure bleed off and starving the engine of fuel at startup. Most common cause is leaking injectors, but considering that the car sat for so long, it could be any part of the fuel system causing the problem.

Vader

92RD has a good suggestion - Test fuel pressure. My guess is that pressure is on the low end and is contributing to a lean condition on cold starts. But that's just a guess, and only testing fuel pressure will reveal the answer. Further, low fuel pressure does not allow the injectors to atomize fuel as well, creating streaming rather than atomization. Warm engines and intakes can tolerate that since the latent heat will vaporize the streamed fuel better, but cold engines do not work with it as well, creating fuel pooling in the intake instead of vaporization. Anything less than 11.0 PSIG indicate a potential problem.

As for leak-down over several hours, that most commonly creates problems with restart after heat soak, and not so much with cold starts. The leaked fuel (if through the injectors or TBI seals) can create a flooding condition. This typically clears itself after an overnight cool down since the fuel tends to evaporate out. If the fuel pressure is bleeding back to the tank through the regulator or pump check valves, that should not create a problem whatsoever since the fuel pump runs a two-second prime cycle when the ignition is first turned on, thus the lack of residual fuel pressure overnight is not so much a problem.

NovaDerrik also had a good suggestion - Check the CTS. The ECM reading of the coolant temperature is critical to cold start enrichment. A simple check with an ohmmeter should reveal whether the sensor itself is producing the correct resistance at temperature, and can also be used to verify the presence of a reference voltage on the sensor yellow lead (sensor disconnected).




Another consideration is the fuel injector inlet screens (the plastic ones) in the base of the TBI pod. Any residual gum, debris, bits of varnish, sediment, and other fouling junk could be restricting flow through those screens.

The diesel fuel may have actually helped during storage. It is as much oil as it is light hydrocarbon, and thus doesn't evaporate as easily. I actually mix in some two-cycle oil (along with fuel stabilizer) in the last tankful of fuel before storing cars for the winter months, and since I started that practice over 15 years ago I have not had an injector or pump problem. Before then it was a different story.

I would also avoid the SeaFoam in fuel. Water is not good for fuel injectors, and probably not so good on the pump and other system components. Put the SeaFoam in your carbureted engines if you must, but for the rest of the time it can sit on the shelf between the intake Air Tornado and fuel line Mizer Magnet set. If you want to use water injection to clean the chambers, there is a far better method than SeaFoam.

TheCob

Wow. Thank you for all the replies. Unfortunately I haven't had a chance to get out and check anything. I don't have access to a fuel pressure gauge. The gas tank seems to be pressurized if that matters. It hisses a lot when you remove the gas cap. I will get an ohm meter to check the cts, assuming I can find it, my Haynes manual is next to useless. I have replaced all the gaskets, o-rings, and screens inside the throttle body. When I cleaned it I got a BWD rebuild kit and replaced everything(including fuel pressure regulator) except IAC and TPS during reassembly. I know for sure I need to repair the wire to the fan switch since it is completely severed. I have to turn the A/C on to get the fan to kick on when it gets up to temp. I may need to replace the actual fan switch depending on how it behaves once it is reconnected but that's a separate issue. I'll keep you posted on what I find. Hopefully this will be a simple(cheap) fix once we get it figured out.

TheCob

Update:
Replaced CTS with no effect. I plan on testing the fuel pressure next. Just thinking ahead here, but assuming that the fuel pressure is low, what would the solution be? Since it is a new fuel pump I would think that would be unlikely as the culprit(although it could be). It's a new fuel filter so theoretically no blockage there. Throttle body is clean with new screens, o-rings, and gaskets, but that's after where I would be checking pressure. There are no obvious leaks that would be significantly reducing flow. Maybe a partially blocked fuel line?

A few more questions just for my knowledge since I am not real knowledgeable about auto repair.
1) I see the injectors spraying when the air intake is removed. Is there a way to tell if they are putting out enough flow or atomizing the fuel properly?
2) What part does the IAC play here? Could it be causing this particular issue?
3) How about TPS? or O2 or MAF sensors?
4) What about ECM? Is it possible that it is not communicating with the injectors properly? Not sure how that all works anyway. I probably look foolish asking all this, but I'd rather look stupid and know the answers.

Vader

If you can observe the injectors spraying, they are connected to the ECM. Injector flow and atomization are reliant upon correct fuel pressure and clean injector inlet screens.

The IAC can be wide open at startup and it should not affect the fuel spray or mixture enough to matter much at all.

The TPS sensor should be at or around 1V in the closed throttle position, and is relatively easy to test by back-probing the connector or harness. Actually, as long as it is below 4V the system should operate the injectors.

The O² sensor is not effective during cranking and cold starting. The ECM will ignore the O² sensor completely for fuel trim until the startup timer has elapsed (about 30-ish seconds IIRC), the coolant is at a minimum temperature or about 130°F, and the O² sensor starts to produce cross-counts. Once all three are satisfied, the sensor will be used for reference IF is is active.

There is no MAF sensor on a TBI system, and for that matter, no MAF on a 1991 F-body even with TPI.

The MAP sensor could be an issue, but not for cranking and cold starting. The most important inputs are the CTS and IAT sensors, and of course the distributor reference pulses and correct fuel pressure. Since the injectors are spraying, there must be distributor pulses to the ECM, and of course there must be some fuel pressure. Whether it is adequate or too high is a question to be resolved.