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I had my first real issue with my '86.5 since completing my top-end refresh last fall. I drove it a couple of miles tonight, parked it, and it backfired into the intake when I tried to start it. As you can see in the picture below, It blew the intake plenums loose from the intake runners. I've had it towed home but haven't really looked into it yet.
I've really not had many issues with it running since getting it back on the road last fall and putting about 300 miles on it. The only running issue I've had is a hunting/surging idle when I first start it up. To compensate for this I give it a little bit of throttle when starting it. I then hold it at about 1200 RPM for 10 seconds or so to let it smooth out. That's what I was doing when I started it this time and got the loud backfire.
What am I looking at doing besides reattaching the side plenums and center "T" pipe? I'm thinking I need to check my cam timing to make sure the belt didn't jump with the backfire. Should I expect any damage as a result of this backfire? Let me know what you folks think.
I cannot remember what caused this on my car years ago. Think the MAF was way out spec from using K/N filter. Mine also had hunting idle and I would 'feather' the pedal for a few seconds to achieve idle. Yours really popped, as mine only 1 side came apart. Check all vacuume line. Anywhere vacuume is used may be off now. MAF should be 380 ohm. I was out in middle of nowhere for mine, no phone so I shoved end back on and drove home (didn't really have a choice)
Hi Ethan; “The only running issue I've had is a hunting/surging idle when I first start it up. “
Ditto here in the past and for way too long.
Your fuel pressure regulator and dampeners are likely leaking fuel back through broken vacuum diaphragms to the vacuum source (throttle body and “T” of the intake). Very common. You can easily check this by pulling the vacuum hoses off the reg and dampener nipples. Smell the end of the hose or rub your finger on the end of the hose for hint of fuel. This is an easy fix (replace them), although more expensive than say 5 years ago. Get prices for components from Roger and Greg. They may have different aftermarket parts solutions.
I cannot remember what caused this on my car years ago. Think the MAF was way out spec from using K/N filter. Mine also had hunting idle and I would 'feather' the pedal for a few seconds to achieve idle. Yours really popped, as mine only 1 side came apart. Check all vacuume line. Anywhere vacuume is used may be off now. MAF should be 380 ohm. I was out in middle of nowhere for mine, no phone so I shoved end back on and drove home (didn't really have a choice)
Thanks joejoe. I'm going to start looking through things today starting with my cam timing. I'll just feel better if it's still where I set it. I'll check my MAF but it should be good. I was new last fall.
Hi Ethan; “The only running issue I've had is a hunting/surging idle when I first start it up. “
Ditto here in the past and for way too long.
Your fuel pressure regulator and dampeners are likely leaking fuel back through broken vacuum diaphragms to the vacuum source (throttle body and “T” of the intake). Very common. You can easily check this by pulling the vacuum hoses off the reg and dampener nipples. Smell the end of the hose or rub your finger on the end of the hose for hint of fuel. This is an easy fix (replace them), although more expensive than say 5 years ago. Get prices for components from Roger and Greg. They may have different aftermarket parts solutions.
Hey mj1pate. I replaced the FPR and one of the dampers when I did my top end refresh. That leaves one damper that is old. I'll be checking it while going through everything else I can think of.
Hey mj1pate. I replaced the FPR and one of the dampers when I did my top end refresh. That leaves one damper that is old. I'll be checking it while going through everything else I can think of.
I see. That’s the thing that jumped right out, because I thought you were describing my 86.5 6 years ago. The other thing is don’t trust any OEM vacuum operated device in your car. That $600 aluminum valve fixed to your cross member that helps regulate tank vapor recovery and the little plastic vacuum valve that helps do the same likely leak vacuum. That aluminum valve that regulates air injection.. the same. I’ve had to replace or work around all these when they failed vacuum tests. You can achieve tank vapor recovery without the $600 aluminum valve if yours leaks. If interested , I can direct you to a thread.
I see. That’s the thing that jumped right out, because I thought you were describing my 86.5 6 years ago. The other thing is don’t trust any OEM vacuum operated device in your car. That $600 aluminum valve fixed to your cross member that helps regulate tank vapor recovery and the little plastic vacuum valve that helps do the same likely leak vacuum. That aluminum valve that regulates air injection.. the same. I’ve had to replace or work around all these when they failed vacuum tests. You can achieve tank vapor recovery without the $600 aluminum valve if yours leaks. If interested , I can direct you to a thread.
one last thing: my 86.5 has been thru multiple cycles of MAF/LH/EZK/PR/dampener requiring rebuilds, with engine stumbling or running poorly during the process. All of theses extra rich/lean cycles are h3ll for the catalysts. When I last had my exhaust down, I disassembled the pipes/components and looked directly into the cats and discovered the matrix on both were cracked; one horribly so. There was absolutely no sign of exterior trauma. If you haven’t checked/replaced/substituted for them by now, it’s a good idea to do so
I see. That’s the thing that jumped right out, because I thought you were describing my 86.5 6 years ago. The other thing is don’t trust any OEM vacuum operated device in your car. That $600 aluminum valve fixed to your cross member that helps regulate tank vapor recovery and the little plastic vacuum valve that helps do the same likely leak vacuum. That aluminum valve that regulates air injection.. the same. I’ve had to replace or work around all these when they failed vacuum tests. You can achieve tank vapor recovery without the $600 aluminum valve if yours leaks. If interested , I can direct you to a thread.
Originally Posted by mj1pate
one last thing: my 86.5 has been thru multiple cycles of MAF/LH/EZK/PR/dampener requiring rebuilds, with engine stumbling or running poorly during the process. All of theses extra rich/lean cycles are h3ll for the catalysts. When I last had my exhaust down, I disassembled the pipes/components and looked directly into the cats and discovered the matrix on both were cracked; one horribly so. There was absolutely no sign of exterior trauma. If you haven’t checked/replaced/substituted for them by now, it’s a good idea to do so
Thanks Michael. I would be interested in that tank vapor work around. The original valve had failed. The one on it is off of ebay. It held vacuum before I installed it anyway. I'll be checking it and all other vacuum operated engine components.
I have a set of MSDS headers that I hope to install this summer. The exhaust shop I'll be using to fabricate the pipes, from the headers back, may insist on putting cats back on it. I don't really have an objection to high flow cats being put on it if they insist.
Originally Posted by Kevin in Atlanta
Look for fuel in the shoe below the MAF.
Had this happen on John Guzman's car - the right suitcase took out a fluorescent light bulb as it shot across the shop.
Badda boom, baby.
Kevin
Dam Kevin. I guess I'm lucky it didn't damage my hood. It was loud though. I'll look for fuel and check my FPR and dampers. The engine kept running and was loud. I first thought I'd blown my exhaust. The engine tried to rev up high due to all the extra air flow.
The ironic thing is that this happened right in front of a nearby auto parts store. I had just returned a loaner tool and was trying to leave. I did get a lot of nice comments while waiting for the tow truck though
Well I think I found the likely culprit though I'll be checking other stuff for good measure. The front fuel damper (the one I didn't replace when I did the refresh) has failed and is leaking gas past the diaphragm. I'll go ahead and check my cam timing and a few other things before reassembly and getting it back on the road.
One bonus of having a backfire like this is that it makes short work of removing the side intake plenums.
That vapor recovery valve workaround is described in this thread, below. The aluminum valve is taken out entirely, leaving the plastic valve in and the vapor hose is connected to the blind port in the passenger side of your air filter housing. Yes, you have to drill out a hole in the blind port. The concern us that with a MAF in the vapor path, fuel oil residue could accumulate on the MAF hot wire. I added an inline vapor separator such as below in the vapor recovery hose just before the hose connection to the air filter.
Well I think I found the likely culprit though I'll be checking other stuff for good measure. The front fuel damper (the one I didn't replace when I did the refresh) has failed and is leaking gas past the diaphragm. I'll go ahead and check my cam timing and a few other things before reassembly and getting it back on the road.
One bonus of having a backfire like this is that it makes short work of removing the side intake plenums.
Yup. Raw fuel in the intake system will explode and blow off the plenums.
My timing belt didn't jump so that's good. I'm at 1 degree advance on the left and 3 degrees ret on the right. They are both one degree off from when I set them. That may well be me being tired and not quite getting it exactly to 0|T. I'm not thinking there is real need to retime since it's that close.
05-13-2022, 12:21 AM
1st significant post top-end refresh issue
