97grand4.0

For the longest I had 1 monitor that would not run. (at the moment I have brain fart and cant remember which one exactly). It was the one that is the first one to go on the EVAP system. Anywho..I could pass inspection as an obd2 inspection for a 97 vehicle allows one monitor incomplete so rather than smoke test etc etc and $$$ I let it go.
Fast forward, I replaced the fuel pump and the injectors with 4 holes. Since injector swap mileage on the overhead console has gone from 12.0 to 13 in just a couple weeks.
So today I put the scan tool on. Short term fuel trim 1.6, Long term is hovering around -9 or -10. And what I was stunned to see is all monitors ..complete.
So I wonder...why...was it the injectors or the fuel pump, or the seal on the tank, or none of the above?
Also would anyone pontificate on my fuel trim numbers...good bad or indifferent?? Have never replaced the front O2 sensor..
Thanks in advance

dave1123

It may have been the seal around the fuel pump. On cold startup, the leak detection pump pulls a vacuum on the system and waits for the vacuum level to drop. When the leak gets large enough, it trips an Evap trouble code, either small leak or large leak. I don't remember the numbers. If the tank is full, sometimes it won't trip a code but will when the level is lower. I just had a small leak that turned into a large leak, then eventually started dripping on the ground when you tried to top off the tank. It was the steel filler pipe's small vent pipe rotted out. The end actually broke off when I took it off the tank. Vacuum is one of the hardest things to seal.

97grand4.0

It was the steel filler pipe's small vent pipe rotted out. The end actually broke off when I took it off the tank

U pull U save I found a replacements for that..all plastic. Apparently not all were made of metal, or maybe the 99+ changed. They are quite easy to pull as the tanks are already out. $2.

Hm. Ok sounds logical. I did pay super careful attention to sealing it right, and the pump unit itself was just all around better quality than anything I had before, so that could be it. I also currently have about half a tank so that could help too.

97grand4.0

I'll answer my own question:

Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
-http://www.easterncatalytic.com/education/tech-tips/fuel-trim-can-be-a-valuable-diagnostic-tool/

The reason behind my question is my new $45 Chinese 4 hole ebay injectors..while I see increased performance in almost every way, it does stumble on start up since I put them in, ..am starting to think they may run a bit rich which the pcm and o2 then compensate for. It straightens right out after a minute or two.

dave1123

I think you hit it on the head. Until the 02 sensors heat up and come on line, the PCM uses preprogrammed mixture settings. I noticed this when idling for long periods in the winter waiting for my newspapers and trying to stay warm. I'd get nice and toasty warm, then shut the engine off until I couldn't stand the cold anymore, then fire it up again. It would idle rough until the 02's came back on line. Even though the engine was still at or close to operating temp, the 02's were cold. This is why the newer ones have preheaters in them. Supposedly, 02's don't stabilize until they reach 600*F from the flame of the exhaust.

97grand4.0

Hm. I do believe mine have heaters in them. ..so will the preprogrammed mixture settings eventually straighten out my start ups..?

dave1123

IDK, but maybe eventually. I'm not aware of how much the PCM "learns." I DO know the PCM reads the IAT and MAP inputs to help set mixture along with feedback for the 02's. When I put reconditioned Bosch 4-holers in mine, I got much better idle and throttle response as well as just a little better mileage. It doesn't matter what the flow rate of the injectors is. The PCM controls mixture by varying injector "On-time." What boggles my mind is the PCM can read the exhaust gases from one cylinder and change the mixture for the next one to fire! At idle, that's 2250 times per minute!

97grand4.0

Learns, is the word I was looking for. Am thinking the injectors might have to go. I think the flow rate does matter if high or low the pcm has to trim it to get it to the desired range. If it's too high the PCM can't trim enough. They say something like over 15 either way is too much. I'm seeing a -10 LTFT -10 is how much trim it's having to apply. Its running so much better overall Im probly not gonna mess with it right now but if I do it will be to replace with the bosch.

dave1123

I bought mine on Amazon at $150 for the set. The ad said "various numbers" so I have no idea which ones I have, but they were a matched set for the 2000 WJ 4.0. The whole point is with the 4-holers, the fuel droplets are much smaller so they atomize quickly.

I think they were from K Suspension. Not Amazon.