P1294 CEL code (for idle speed performance)
- Thread starter Austin O.
- Start date
Leak Detection Pump is missing. Look on the emissions page of the FSM for 1998s.
Thank you. So it looks like it’s not necessary to the operation of the car, but mandated by the government??
The leak detection pump (LDP) is used by the PCM for emissions monitors (programs that the PCM periodically runs to make sure your TJ isn't polluting the air). The following codes can be occasionally triggered by the leak detection system:
P0442
P0455
P1494
P1495
That system has no measurable effect on performance or durability. As Andy-WhiteTJ pointed out, the "Emission Control Systems" section of the FSM is very informative in understanding the basics of how things work.
Apparently, the LDP wasn't on all TJs, though, so it may not be missing:
I'm guessing that if you've run that TJ for more than a couple weeks, and you haven't gotten any of those codes above, your TJ wasn't "equipped with certain emissions packages." However, that port should still be connected to something. Unfortunately, the system schematic at the top of page 25-13 in the FSM does not show how things are connected if the LDP is absent. The other things to which your open port could be connected are the evap charcoal canister (the big rectangular box above the driver-side wheel well) or, more likely, the purge solenoid (the thing on the inside of the canister with the green port on it for smoke testing.) The purpose of the canister is to collect fumes from the gas tank and trap them. The purge solenoid is then opened under certain conditions by the PCM and vents the fumes to the intake manifold so that the engine can burn them. The two hoses or tubes connected to the purge solenoid should go to the canister and the intake manifold (one to each.) I see two hoses, but can't see where they go. Where do they go?
I have ordered a bolt with the correct thread size to put in there. Did this temporarily. The local hardware store didn’t have the right size in stock. Is just putting a bolt in there an okay way to do it? I don’t see why not…
A bolt? I’d remove it and replace it with a pipe plug. Hard to gauge size from that photo, but my guess is 3/8” NPT.
I didn't realize that some didn't come with the LDP. If his did, he would have an electrical connector hanging near that area to go to it. If he doesn't have that connector, I would assume his was not equipped. Mine has California emissions. His may be just Federal emissions.
The late 90s were a time of great change in emissions requirements. OBD2 started getting mandated around 1996. Before that, OBD1 was not a required standard, but OBD2 was a federal requirement. Also, CARB, the California equivalent of EPA, had independent requirements that were more strict than the federal requirements, and eventually, many of those requirements were adapted federally. I don't know the timeline of all that, but I suspect that you are correct. Back in that time frame, we referred to vehicles meeting CARB requirements as CA vehicles and everything else as "49-state" vehicles.
But something had to go there?I can’t imagine driving around with that massive of a vacuum leak.
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