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Old 07-02-2019, 01:29 PM   #1
Join Date: Nov 2015
Posts: 31
IAP sensor replacement

I am going to replace my IAP sensor # 224-4536, and I have a few questions.
1) I see many sensors advertised on eBay as OEM or genuine for about $26. The price from Cat is about $150. Are the eBay ones reliable or to be avoided?
2) Do I need any sort of o-ring, crush washer or gasket for this replacement? If so, anyone have a part number?
3) As I have struggled to diagnose this issue my ECU seems to finally have gone into limp or depower mode. Is there a way to reset this such as disconnecting the chassis batteries?

2002 Fleetwood Disco w/ 3126B 330hp

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Old 07-02-2019, 06:51 PM   #2
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I have replaced many IAP's for people. I tried an "Ebay" sensor ONCE and only ONCE. It lasted about two months and down to the Cat dealer I went. Rare I found the ECM threw a code for the IAP. Unplug the 3 pin connector and start the engine. If it starts and idles fine then it is defective. Otherwise you have other issues. What code are you seeing?
Good luck!

George and Diane, 2004 Discovery 39S pushed by our Keywest CC w/115 Johnson
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Old 07-02-2019, 08:03 PM   #3
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But the bullet and buy CAT. and yes replace the o-ring
Dale&Susan, 08 Alfa Gold, DaGirlsRv Blog
2015 F-150XLT_1600W Solar_880 AmpHr
Magnum_MSH 3812 & PT100
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Old 07-03-2019, 05:43 AM   #4
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The code is a 164-2 on my Scangauge (erratic Injection Actuation Pressure). Symptoms are hard starting, an occasional erratic RPM in neutral at, say, 1200 RPMs and occasional sharp drops in RPM at idle.
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Old 07-03-2019, 06:14 PM   #5
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Did you try the unplug? Sounds to me like an "erratic" IAP. Seen it many times before.
By the OEM replacement, about $162.00 bucks at mine in Cleveland, Ohio. Be sure to have your serial number handy.You can also check the supply voltage at the plug: 5vdc
George and Diane, 2004 Discovery 39S pushed by our Keywest CC w/115 Johnson
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Old 07-04-2019, 02:19 PM   #6
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I had my IAP replaced on Monday at Western States Cat in Kalispell, MT. My Scangauge D did not pick up an engine code. My failure was also erratic, Check engine light would flash on and I'd loose power, but would clear right away. Seems like they should have diagnosed my trouble quicker than they did (thought I had a broken wire), but they got me back on the road.

Home, but now I have an oil leak.
2003 Allegro Bus 35'
330 Cat
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Old 07-09-2019, 02:06 PM   #7
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Thought I would post a follow-up.

I disconnected the existing IAP sensor and the rig started right up and idled smoothly. I then replaced the sensor with the OEM Cat part and o-ring, which was easy going through the bedroom floor. I started it up again and it idled smoothly. It looks like that solved the problem.

I'm still wondering about the limp/depower mode, though. What do I need to do to get the ECU out of depower mode?
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Old 07-09-2019, 07:24 PM   #8
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I had a crank/no start issue last month, the night before a big trip in my driveway. After some research here on IRV2, I found a post that exactly matched my issue. Low mileage (27,000) 2003 Cat 3126E, crank no/start. I disconnected the IAP sensor (after taking a few minutes to find it) and the rig started right up. I called my local FL dealer the next morning and installed the sensor in about 10 minutes. Luckily they had one in stock. I also got a new O-ring. Fired right up and worked perfectly throughout my trip. I'm thankful for this forum.

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Old 07-11-2019, 03:20 PM   #9
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Regarding a sudden starting issue when your coach ran normal.

I have experienced customers that was told by repair houses that many other expensive components were failed to only find a $162.00 IAP sensor had failed. Some had HEUI's replaced by "recommendation", guessing I call it, and paid a very expensive repair bill over the IAP failing. Not to say other sensors cannot or will not fail, only that my experience has proven the IAP is my first diagnostic choice when hard starting, black smoke or rough idle is present.

Puffy black smoke usually indicates the IAP is stuck in a no pressure feedback condition so the ECM drives the HEUI to max pressure. Conversely, if the IAP sticks when the common oil rail pressure is high, Engine load is high, then the ECM drives the HEUI to little or no pressure, thus no injection pressure of fuel, hard or no starting condition.

The term "sensor" regarding the IAP means it is a pressure transducer. It receives 5VDC from the ECM and converts pressure into an analog signal back to the ECM so the ECM knows what current to drive the HEUI pump pressure. The ECM calculates the fuel required to satisfy not only the IAP but in combination with other sensors.

Debris between the HEUI and the common oil rail in the head can and will "stick" the IAP actuator piston. The clearances are very close and any debris from the HEUI or poor oil change maintenance can cause the IAP to fail or stick.

If you maintain frequent oil/filter changes and experience IAP failures frequently then you are most likely experiencing a HEUI on its way out. This condition is telling you that debris is coming from somewhere and most likely Mr. HEUI.

Safe travels to all.

George and Diane, 2004 Discovery 39S pushed by our Keywest CC w/115 Johnson
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ace, replace, replacement

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