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Hi to who ever sees this. I have a vacuum leak in my 98 Jimmy, I’ve checked all the lines I can get to at the moment but the leak is so bad that its causing an extremely rough Idle and upon a cold start the rpms sit at about 1400. I know the leak is somewhere in Bank 1 of the engine I just don’t know where else to look. I’ve replaced the pcv valve and checked all the main lines after the MAF but nothing still. I can not find this leak with carb cleaner or propane I’ve tried both, and I do not have access to a smoker I’m on a budget lol which means I’m broke. I’ve driven my wife crazy trying to find this leak but it still eludes me 🙁 and today 11-12-17 I was on my way home and the truck started to sputter and then died on me as I was getting one hell of a knock from the rear of the truck. I thought it was the fuel pump but I had someone listen for it to turn on and its working fine as far as I know. Also I know the tank had about 4 gallons of gas in it so I didn’t run out of gas unless I burned threw it all which is ridiculous if I did because I had just put that gas in it the night before this happened.
If anyone has any suggestions or any similar issues with this year/make of truck PLEASE help me I need my truck for work.
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To a degree, this sounds like a false lean problem to me. Can you look at any PID data with a scan tool at all? I’d want to look at fuel trims and O2 sensor data first and then maybe MAF/MAP data later. If you want to try it on a shot gun diagnostic, just unplug the bank 1 pre cat O2 sensor and see if it runs better.
I also forgot to mention that there is a lot of hesitation when applying the gas from a dead stop, and its also very sluggish.
’98 so probably has CPI injection (I don’t think V6’s ever had SCPI but I could be wrong). This has a central injector with 6 poppet valves that go to each cyl. I have read about problems with the poppets plugging shut with carbon deposits or sticking open. All this sits under the intake manifold. I have not worked on any vehicles with this system so I’m definitely not an expert. As far as engine dying while driving, I’d check fuel pressure. CPI-SCPI need good fuel pressure to open the poppets. Just a suggestion.
if you don’t know anybody with one, you can buy a smoke tester on eBay for $80 or DIY for half that.
A smoke test is by far the best way to find vacuum leaks.
That said, the previous posters are right that you can’t assume this is a vacuum leak. As NCS said, read the OBD data to diagnose the problem.
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