White smoke on decel????
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New User
Joined: Jul 2006
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White smoke on decel????
Hi Guys, today I noticed white smoke every time I backed off of the throttle. I t only occurs when I slowly back off the throttle. It runs fine at speed, If I keep the peddle somewhere between accel and idle it starts to miss. I have 117k miles, original pump and injectors, so I figure the problem may be a bad injector.I assume that if I had a cylinder with low compression it would smoke all the time. What do you all think?
1994 7.3 IDI turbo, pump turned up 2 flats, modified air intake, 3.5" exhaust
1994 7.3 IDI turbo, pump turned up 2 flats, modified air intake, 3.5" exhaust
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
Do you use fuel additives every fill........ stanadyne or power service etc.....
If those are the OEM IP and injectors then any injectors that are NOT up to spec will change the timing in their cylinder..... The IP could be at the end of its usefull time life but not mileage life........ Two choices......new IP and injectors with a good engine timing or new injectors and an old IP and timing set. This would give you some time to check the IP out on the street while driving.
Check the manual lift pump pressure too......
Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when cranking. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of engine cranking, route fuel to a suitable container with a hose.
If those are the OEM IP and injectors then any injectors that are NOT up to spec will change the timing in their cylinder..... The IP could be at the end of its usefull time life but not mileage life........ Two choices......new IP and injectors with a good engine timing or new injectors and an old IP and timing set. This would give you some time to check the IP out on the street while driving.
Check the manual lift pump pressure too......
Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when cranking. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of engine cranking, route fuel to a suitable container with a hose.
Tuned
Joined: Feb 2005
Posts: 380
Likes: 1
From: ohio
My son's 92 7.3 non turbo had those same symtoms (along with others) and we progressed through all the steps as suggested here and it wasnt fixed until we had the IP rebuilt.
Basicaly you check the things that PLC7.3 suggested. I would start at the cheap fix and proceed to the highest cost, the I.P. Something like this;
Has it lasted through several tanks of fuel?
Check for air by checking at the return.
Check lift pump performance.
Check the crankcase breather valve.
Put some good dope inthe fuel.
Replace fuel filter
Check compression (gage kit is $24 at Harbor Frieght)
Injectors (make sure you get the right code)
Pump.
The particulars of all of doing these things can be read by searching this forum.
Basicaly you check the things that PLC7.3 suggested. I would start at the cheap fix and proceed to the highest cost, the I.P. Something like this;
Has it lasted through several tanks of fuel?
Check for air by checking at the return.
Check lift pump performance.
Check the crankcase breather valve.
Put some good dope inthe fuel.
Replace fuel filter
Check compression (gage kit is $24 at Harbor Frieght)
Injectors (make sure you get the right code)
Pump.
The particulars of all of doing these things can be read by searching this forum.
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Joined: Jul 2006
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Thanks guys, I'm not sure if this just started. I just happened to see it one morning in the side mirror. I have use Lucas fuel additive but none was used in this tank. Would a bad IP cause this only when getting off of the throttle? Also, how do you feel about rebuilt IP's and injectors vs new? I have priced both on E-Bay from a place called Diesel Care, they are rebuilt parts, Not sure if this is the best way to go.
Tuned
Joined: Feb 2005
Posts: 380
Likes: 1
From: ohio
You can read both good and bad about Diesel Care. I bought rebuilt injectors from them and they have worked perfectly so far. Had the IP rebuilt locally. I am a long ways from a diesel 'spert from from what I gather smoke when letting off the throttle is from late or "lazy" injection at lower delivery rates (foot off the throttle). If fuel quality, air bubbles and filters are ruled out then your off to the hard stuff. Worn pump parts cause a lag time in pressure build to pop the injector or dribbling injectors will leak out the small about of fuel needed to idle before they should. If your truck smokes a puff after short term idling such as a traffic light stop that would point me to injectors and IP. All of them will puff a bit if idled for long periods.
Posting Guru
Joined: Oct 2005
Posts: 1,030
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From: Powell River B.C.
If you have sorted through all the return line and filter items as acceptable, then I would lean towards the injectors being worn. I replaced mine at 240 K km, that's about 150K miles. They were over due for replacement at that point, always smoked at idle. I bought rebuilt from diesel care, no problems. Injectors are relatively cheap and made quite a differance in my milage and performance, I would start by changing injectors and having the timing checked before I did the IP, with the miles on your truck should have lots of life yet!
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New User
Joined: Jul 2006
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Thanks for all the info...I remember switching to the rear tank which may have had some pretty old fuel in it. I'll start checking my filters and lines.
I have read on here that you should change the IP and injectors at the same time, due to having a worn pump trying to overcome new injector springs. Anyone agree with this?
I have read on here that you should change the IP and injectors at the same time, due to having a worn pump trying to overcome new injector springs. Anyone agree with this?
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Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
Replacement of both at the same time is best, along with a new fuel filter just prior to IP replacement.........
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