Chevy starting complains

[Tanner]

On my 1996 Chevy k1500 with a 350 vortec today I started it and backed it up to the garage to load some stuff in it. I meant to leave it running but out of habit turned it off. I went to start it again and it acted like it wasn’t getting fuel. It would stumble and try to start but no go. After turning over for quite some time I gave it has with the gas pedal like on the old carb engines. And it struggled some more and started.

This is my daily driver so It makes me kind of nervous. It has 230,000 miles on it. It has a newer fuel pump, plugs, air filter, wires, distributor, cap and rotor as well as a fuel filter.

I have noticed it seems to have less power than it should and I’ve lost about 2-3 mpg. So iv been watching my fuel trims and all the good stuff. It idles usually at 800-1000. My long term fuel trims hang out at -4 to -7. My coolant temp only ever runs at 182 sometimes up to but rarely 188 if I am going over a lot of hills. My temperature gauge in the dash only shows me 150 or 160 so one lies. Iv also been watching my O2 sensors the change a lot like they should but get hung up in the 85 range for 3 or 4 seconds. To my knowledge they have not been replaced. What are your thoughts? Thanks for your help

Topic

[Kirk]

No codes? Sorry I cant be of much help except 1 suggestion.

Any oil on any of the spark plugs?
My valve gasket went out and that happen to me, fine and then just a horrible time getting it to start. Was oil leaking through gasket onto plug 1 and its boot.

I am sure someone more knowledgeable will come along.

[Gary]

I would run a compression test. Your Fuel trim is on the rich side as well have you checked for vacuum leaks? ECM could be adding fuel due to more O2 reaching the sensors. Since you mention a high idle(800-1000) is high for a stock engine, it’s quite possible you have developed a vacuum leak. There are alot of possibilities, lets start to narrow it down.

[Tanner]

Correct me if I’m wrong but wouldn’t a negative trim mean it was trying to take fuel away? Or do I have that backwards? I checked for vaccuume leaks today but couldn’t find any. I watched my O2 sensors they seem to be switching. Although one got stuck and would only switch between 2 and 8 for about 5 seconds. If I turn the key on and nothing else my O2 sensors seem to be random. Sometimes they will match and be at 43ish and stay and sometimes one will be way different than the other and almost bleed off. Sometimes one will read 0 for a short time. I didn’t think it should but I don’t know that for sure.

[Tanner]

Oh I looked for oil too and didn’t see any. And I didn’t get a chance to pull my plugs

[Gary]

[quote=”Passey” post=129464]Correct me if I’m wrong but wouldn’t a negative trim mean it was trying to take fuel away? Or do I have that backwards? I checked for vaccuume leaks today but couldn’t find any. I watched my O2 sensors they seem to be switching. Although one got stuck and would only switch between 2 and 8 for about 5 seconds. If I turn the key on and nothing else my O2 sensors seem to be random. Sometimes they will match and be at 43ish and stay and sometimes one will be way different than the other and almost bleed off. Sometimes one will read 0 for a short time. I didn’t think it should but I don’t know that for sure.[/quote] I phrased that very poorly. It is subtracting fuel due to running rich. So, yes you are running rich. It’s possible the O2 sensors are defective which are causing a rich condition. Your fuel mileage is suffering because you are clearly not running stochiometric. Another possibility is you have a compression issue and not all the fuel is burning, going out the exhaust and causing a rich condition to the O2. This would cause the O2 sensor to input to the comp to subtract fuel and kill efficiency. There are many possibilities, have you scanned for codes? I would run a compression test to rule out mechanicals, double check the fuel and ignition systems and go from there.

[Tanner]

I did some adventuring today and discovered a couple things.

I checked once for for vacuume leaks and again didnt find any.

my boss thought maybe my distributor worked loose and maybe turned a little. I checked and its pretty tight and I couldnt move the distributor.

I was thinking and decided that I had replaced all the ignition parts except the coil which I had tested before and found that it failed a resistance test but i didnt have the money then to replace it. if that was the problem it would make sense because it wouldnt produce a good spark to burn all the fuel making it rich. if that theory makes sense. it does in my head anyway.

I decided to look at the k&n air filter I have in it. It doesnt look bad by any means but I dont think it will hurt to clean it.

I did a compression test on 4 of the cylinders (thats all the time I had before an appointment) and all four were in the 135-140psi range. the spec on these motors is no less than 100 psi and no less that 70% of the highest. but I dont know that it would be ok to have that much variation. I had always heard within 10% of the other cylinders.

I looked through the plug wires adn there wasnt any noticable arcing or rub spots.

I am still questioning the O2 sensors a little bit but they seemed to respond to a unmetered air and extra fuel.

Last but not least I noticed a small wet spot under my brake master cylinder. upon further inspection it was indeed brake fluid. the brakes on this truck are something that I have been chasing ever since I bought it. I have replaced almost every part of the brake system other than a couple lines, the booster, and the adjusters/springs for the drums. I just replaced that master cylinder last year. but it came from a place where I have had several parts now go bad prematurely. and I am not the only one. I do not shop there anymore and a new napa auto store has moved into the town so thats where I get my autmotive parts now. or online. havent had any problems yet and iv heard they have great customer service plus I know the family that runs it.

So my first adventure is to replace the master cylinder again. I was wondering if it was possible that something to do with brake fluid in the booster was hurting my mpg?? it is hooked directly to the intake vaacuume. I hope to have the master cylinder bench bled and on this saturday.

[Author]

Replies