 question on backfire, spitting back through throttle body.... |
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| crash914 |
 Nov 3 2004, 06:26 AM
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its a mystery to me  Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region  |
OK, I know that I don't have my fuel ratio down yet...laptop hard drive failed....so I hooked up my MS that was set up for the stock 2l on my 2.7....
I have changed out the stock FI system for twin dual throttle bodies... I havent got it running well enough yet to get a low rpm to set timing...but I can blip the throttle to maintain 2 3K rpm. I know that my cold start is lean, and when cranking it sounds like running on 2 cylinders...when it warms up, I can get it to rev... again, my fuel maps are off.....when cranking, it sounds like cylinders 3 and 4 aren't kicking...when I get sustained running, it spits back in cylinder 4, cylinder 3 seems ok and the firing order is correct. I have swaped injector wires to see if it was a signal problem....no.... What would cause backfire/spitting back through the throttle body? 1. lean condition in cylinder----yes, most likely...although I do read 14.5 on my wide band... 2. Loose exhaust valve clearance....leave pressure in cylinder that spits back through the intake valve 3. Tight intake valve....see above 4. ?????? I am running a 163/86b cam on a 103 by 80 motor...... I should have a laptop to hook up to it by this weekend.... thanks, herb |
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| crash914 |
Nov 3 2004, 09:46 AM
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its a mystery to me Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region |
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| mike_the_man |
Nov 3 2004, 11:12 AM
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I like stuff! Group: Members Posts: 1,338 Joined: 11-June 03 From: Regina, Saskatchewan, Canada Member No.: 809 |
Not sure if this will be any help, but my car was doing the same sort of thing. It turned out to be a few pretty major exhaust leaks right at the heads. It wouldn't hurt to make sure the exhaust is all sealed up.
(IMG:style_emoticons/default/confused24.gif) If that's not it, then it's probably running lean. Like I said, probably not much help. |
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| crash914 |
Nov 3 2004, 12:07 PM
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its a mystery to me Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region |
you could be right, I did think that I heard an exhaust leak....but it was doing the same thing with no exhaust on at all....I will look at it..thanks!
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| rhodyguy |
Nov 3 2004, 12:23 PM
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Chimp Sanctuary NW. Check it out. Group: Members Posts: 22,080 Joined: 2-March 03 From: Orion's Bell. The BELL! Member No.: 378 Region Association: Galt's Gulch |
like dual carbs, do the butterflies open and is the flow at the same rate? the linkage must still be dialed in.
kevin |
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| crash914 |
Nov 3 2004, 12:49 PM
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its a mystery to me Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region |
I did look at the linkage...both seem closed the same amount and open to the same position....
I have not yet set the air bypass for idle air yet...this is something I want to do after I can get somewhat of an idle.... THanks for the insite...herb |
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| Mueller |
Nov 3 2004, 01:26 PM
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#7
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None 
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O2 sensor reader
you really should invest in one of these (IMG:style_emoticons/default/smile.gif) to help ease the pain, get a few local people you know/trust to go in on the purchase.... sounds like it's really lean right now.... |
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| crash914 |
Nov 3 2004, 02:09 PM
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#8
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its a mystery to me Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region |
Muller....it is lean at idle....I do have a WBO2 set up..AFR is arould 14.5 at 2-3000 rpm...my laptop is broken so I can't adjust the pulse width until I can get the laptop back in operation....
IF it is just an AFR problem...that is an easy fix....it could be as it is very hard to start cold...thanks, herb |
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| john rogers |
Nov 3 2004, 06:48 PM
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Senior Member Group: Members Posts: 1,525 Joined: 4-March 03 From: Chula Vista CA Member No.: 391 |
I would say lean is the problem. A lot of the vintage race cars I race with are lean at about 1200 RPM or so and they (as does mine) spit and pop back through the carbs a lot. Once the RPMs come up the mixture goes richer and the poping goes away. If it were me I would not run it until you can richen the mixture a bunch as the 14.5 is too lean as I like it 13 to 1 or so. I would also pull the injectors and put each into a jar or container and see if they are flowing equally and have good spray pattern. Good luck.
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