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Hi MAP value ***FIXED***

Posted By Steve'o Monday, December 04, 2006 7:00:38 AM
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Steve'o
 Posted Monday, December 04, 2006 7:00:38 AM
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Hi chaps, wondered if you could help me with this one.

got a 2001 Jeep Cherokee 3.7 v6 (petrol) in the shop today with a miss fire/stutter (through out the rev range inc idle). No fault codes. DRB3 is'nt picking up the miss fire. When reved sounds like a carb with to much choke. Checked the spark plugs, three shades darker than a crow and a little past there best. Checked sensor readings with DRB3 (Jeep scan tool). CTS and ATS ok. MAP 2.4v. Injectors 8ms. All readings taken at idle with TPS showing 0%. Compared these readings with a good Cherokee. MAP 1.7v. Injectors 3.4ms. swaped MAP sensor, no change. Swaped PCM, no change.

Have you any idea why the MAP would be so high at idle? The engine is running rich. Checked supply and earth to MAP, ok. Bit stumped with this one.

By the way, I am now living in Australia and this is an oz spec car. Dont know if this would make any difference.

Wednesday, December 06, 2006 8:27:58 AM by DaveH
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 Posted Monday, December 04, 2006 7:41:06 AM
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Is the temperature sensor/wiring ok?

Could be on cold start enrichment permanently?

DaveH
 Posted Monday, December 04, 2006 8:25:29 AM
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Can you get a vacuum reading at idle ?

Regards

DaveH

  
 
 
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cartech
 Posted Monday, December 04, 2006 8:35:45 AM
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DaveH took my words... T-piece the map sensor and check the true reading. It should be approx 18mhg at idle, If it's about 10-12mhg it would indicate a mechanical fault, but if the reading is approx 18mhg, you probably have a bad MAP sensor or wiring.

If I understood women as well as I understand cars, I'd be the envy of every man.
andyfanshawe
 Posted Monday, December 04, 2006 11:57:54 AM
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cartech (04/12/2006)
DaveH took my words... T-piece the map sensor and check the true reading. It should be approx 18mhg at idle, If it's about 10-12mhg it would indicate a mechanical fault, but if the reading is approx 18mhg, you probably have a bad MAP sensor or wiring.

Hi Steve.  Bet your vacuum gauges are still on the boat betwix GB and Oz still aren't they?!BigGrinTongue

Can you rustle up one from someone else?  Or do you want to borrow mineHehe

Andy. 

Steve'o
 Posted Tuesday, December 05, 2006 6:19:14 AM
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Hi chaps.

Thanx for your assistance. Unable to do a vachume check, non of my colleges has one and mine is still in a container floatting around in the south pacific! After a rethink and a bit more testing, im 99% sertain the CAT's are blocked. This would explane the stuttering and lack of power. Correct me if im wrong, but I also think this would caurse the high MAP reading. On the basis that the exhaust gases can not be fully expeled due to high back pressure, thus not alowing the cylinders to have there full swept volume, cauresing a low vachume in the plenum. Hope this makes some sense. Will keep you informed of the rusult if the customer has the CAT's replaced.

cartech
 Posted Tuesday, December 05, 2006 3:21:54 PM
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Your analogy is correct. A restricted exhaust flow will cause a poor vacuum, however it could be a collapsed box.

If I understood women as well as I understand cars, I'd be the envy of every man.
Steve'o
 Posted Wednesday, December 06, 2006 5:27:40 AM
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The plot thickens!

Had the CAT's replaced today by an exhaust center on the customers behalf. Picked the car up at lunch time  to find that the problem had got worse. The engine speed now fluctuates under load and the MIL comes on. Checked for a code, found P0300. No surprise there. Checked the MAP, 1.7v (ok). Checked injector duration, 4ms (ok). So the engine must be breathing properly but still stutters/miss fires. So I then swaped all 6 coil packs from a good car and hay presto the engine ran without a stutter in sight. I then refitted the original coils one by one to find how meny were dud and found two. I then tuck a closer look at the coils. I found that the stem of the coil is made of two parts, joining about half way down. The lower part fitting around the spark plug and the top half containing the coils and trinal that connects to the top of the spark plug. The lower part fits inside the upper and has a shoulder which the upper part buts up to. On the two dud coils there was a gap of about 5mm between the upper part and the shoulder. On the ok coils there was none. This gap would pull the terminal 5mm away from the spark plug, leaving the spark an extra gap to jump. And despite fare means and foul, I couldn't get the two halfs to slide back together. So two new coil packs have been ordered.

Hope you have found this as interesting as I have


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