Backfiring into intake, timing issue?

Dylpro

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Hello all, first time poster, second time SHO owner. This is a long one. My first car was a ‘94 SHO and always wanted to get my hands on another. Fast forward 8 years and I bought a ‘95 ATX as a car to get me back and forth to school and work. Unfortunately about 1 week into ownership the idler pulley grenade itself into the timing cover. I’m going to school for automotive technician at a local trade school and thankfully have been able to work on the car there in between class time since the middle of November.

I’ll fast forward to where I’m at currently, since it’s been nearly two months I’ve been working on the car and many parts later, the engine is back together only to be met with continued trouble.

First attempt to start the vehicle and it’s backfiring aggressively into the intake. The car tries to start but is behaving like it’s out of time. Remove the timing cover and dampener and it appears the timing is correct. Double check the routing of the plug wires (I did have 5/6 reversed at the coil pack but after correcting this it still has the same issue).

I have a video of an attempt at starting that I’ll try to get uploaded, currently writing this on my lunch break. I’ll post the laundry list of parts that were replaced as well.

Basically, I’m at a loss of where to go next. Next plan is a compression test, but a visual inspection of the pistons with a bore scope showed no obvious signs of damage on 4 of the 6 cylinders (ran of of time Friday to check the last 2).

Here are the parts that were replaced:
All gaskets up to the valve covers
Front main seal
CKP
Crank sprocket and backing plate
SHO Source timing belt kit (both pulleys and the solid tensioner)
SHO Source intake couplers
Denso Double Platinum Plugs/NGK plug wires
 

Dylpro

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Not that this will be necessarily helpful but this is the engine as it currently sits. There are some odds and ends still needing the be reassembled/replaced, but this is it at the first attempt to fire it up. I’ll try to get the video I have of that attempt, but as of now I won’t be able to get more photos/videos of the vehicle until Tuesday

Essentially asking for any ideas on what stupid things I could be missing that would make the car behave as if it’s out of time before diving too deeply into a second disassembly
 

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luigisho

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So it was running ok before the idler broke? If so, then it is your work and you will have to tear into it. Other things to check is firing order again, and vacuum leak at the intake or other hose. If you pulled the intake off as one piece (as we all do) and replaced it without loosening the clamps on the rubber couplers (or silicone looks like on yours) you need to have them a little loose to get the bottom of both sides to mate up to the heads nice and flush and retighten the couplers. Also, it is possible to pinch a small vacuum hose in the back when tightening the intake to the head. BTDT a long time ago.
CLogged exhaust can make it run funny but if it was ok before you dug into it...I would go with initial run through error. It happens all the time.
 

Dylpro

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So it was running ok before the idler broke? If so, then it is your work and you will have to tear into it. Other things to check is firing order again, and vacuum leak at the intake or other hose. If you pulled the intake off as one piece (as we all do) and replaced it without loosening the clamps on the rubber couplers (or silicone looks like on yours) you need to have them a little loose to get the bottom of both sides to mate up to the heads nice and flush and retighten the couplers. Also, it is possible to pinch a small vacuum hose in the back when tightening the intake to the head. BTDT a long time ago.
CLogged exhaust can make it run funny but if it was ok before you dug into it...I would go with initial run through error. It happens all the time.
Thanks for the response! It was running well before the idler went, driving to work that day and the engine just completely cut out without warning. No nasty noises to suggest something major at the time, what we first suspected was fuel pump then turned to crank sensor before finally revealing the blown idler upon disassembly.

I’m certain there’s something I’ve done (or rather haven’t done) that is leading to the issue, just having trouble figuring out what it is at the moment.

I found a thread on here yesterday that had a breakdown of the lines removed during intake disassembly and while I believe I got them all reattached properly that will be one of the first things I check Tuesday.

I’ll find a way to upload the video of the startup
 

Irish Pride

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Double check your plug wire routing. It's very easy to get it wrong. #5 and #6 are backwards on the coil.

Engine =
1 2 3
4 5 6

Coil =
5 1
6 2
4 3

-Chad
 

Dylpro

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This video probably won’t be all that useful but best I have available at the moment, here

This was after switching 5/6 on the coil pack as I had those reversed at first. I’ll be sure to check the wire routing again.

When reinstalling the intake I had had trouble getting it to sit flush at first and had loosened the couplers before finally getting it to line up ~enough~ to be able to screw it back into place. Now I’m wondering if it may not have been perfectly meshed in doing so or if I possibly pinched a line.

The only lines I had trouble with specifically were the line going to the EGR and the PCV, both of which were replaced
 

luigisho

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Yeah my first or second time taking it off I was in a rush and it was getting dark working in the driveway. I got it to what I thought was seated correctly and I torqued it down pretty good. Ran like doo doo and when I pulled the intake back off I saw the small hose I smashed real good. Lots of things like that happen with timing, spark plug wire routing etc. I know I did it right.. but not really after going back.
Same stuff happens when you get a part that is garbage out of the box. You cross it off the list of possibly the issue until finally you give it a shot as possible, and there you are. I had 3-4 alternators bad out of the box one time and I thought that was statistically almost impossible. It's just part of the game.
 

BaySHO Performance

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First off is to pull the codes to see if they tell you anything. Be aware that very few of them will throw the Check Engine Light. Your Gen 2 will have three digit codes:


If no codes, the problem is usually a bad plug or wire, or a vacuum leak.
Difficult to hear on your video where the misfire is occurring. My car makes a soft pop sometimes when cold at low revs, but that's nothing to worry about. However, if it's a loud bang, it may have damaged one of the cats. I suggest checking them out once you have fixed the problem. Ideally with a borescope, or run something long and flexible into each end to see where it stops. If you have a damaged cat, a piece of material could have got stuck in the cat back, robbing you of power because of the excessive back pressure.
 

Dylpro

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So I was able to pull some codes, might try it again because I’m not sure exactly when the codes stopped flashing, we ran it twice, first time I got some numbers I didn’t get the second time so I want to run it a third time to make sure.

Codes I got for sure:
335
558
565

Codes I’m unsure of from the first test
121 and 112. Unsure because I got the test light hooked up late in the process.

Compression was good at all cylinders as was fuel pressure. We’ve noticed the plugs are fouling out almost immediately.
I replaced the denso’s with the original plugs that we took out which were in decent condition. The vehicle did try to start better with the fresh plugs but very soon after went back to backfiring. The Motorcraft plugs that were in decent condition quickly fouled out, within 30 seconds of trying to get the vehicle to start
 

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BaySHO Performance

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So your first test was a KOER. Always best to first do a KOEO. None of those codes would cause a misfire.

Why the plugs are fouling up so quickly is a mystery. The black soot shows that the car is running rich. This could be because of old O2 sensors, although no codes came up for them.

Were all the plugs the same, or was there a difference between them? Might point to a bad plug or wire.
 

Dylpro

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So your first test was a KOER. Always best to first do a KOEO. None of those codes would cause a misfire.

Why the plugs are fouling up so quickly is a mystery. The black soot shows that the car is running rich. This could be because of old O2 sensors, although no codes came up for them.

Were all the plugs the same, or was there a difference between them? Might point to a bad plug or wire.
All of the plugs turned to that shortly after trying to get it started. I’ll run codes now for KOEO and see what I get. All 6 of the new plugs were Denso double platinums and the plugs they replaced were Motorcraft. The plugs were still clean so when we realized the Denso’s had fouled out we put them back in, pulling plug 4 showed the same black soot.

Within 30 seconds of a few attempts at starting the Motorcraft look the same as those Denso plugs. All 6
 

Dylpro

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I have class from 12:30-4:30pm CT but afterwards I’m staying to continue working on it so I’ll be able to try any suggestions presented. Thanks again for the help so far!
 

Dylpro

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With all the codes seemingly pointing towards EGR my instructor suggested trying to block off the EGR to see if it runs to determine if the EGR is stuck open, which was one of the trouble shooting items I found for the black soot appearance of the spark plugs through Prodemand.

One of the other instructors suggested clearing the codes by letting the battery cables touch for ~10 minutes and resetting keep alive memory, his theory being that the car may be using the timing sequence from when the pulley gave out? I’ll be honest I didn’t entirely follow what he was saying in this instance.

I’ve got the next 4 hours and the entire selection of tools in the shop at my disposal so I’ll check back here if I discover anything else, will also try to get a good video of the engine during cranking
 

Dylpro

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So I feel like an idiot. We plugged off the EGR and the backfiring stopped, but it was back to behaving the same way it had when the timing pulling first went, cranking but not firing at all. The backfiring did stop though.

So I was surfing threads through here and other areas and found one mentioning ground straps and assuring they were all hooked up properly (may not be still but I’ll double check those on final reassembly).

While searching for the passenger side ground strap by the bracket I noticed the connector to the CMP was broken and only loosely connected.

Pushed the connector back in and she fired up without hesitation. Thank you all for your suggestions! I’m cautiously optimistic now, will report back once I’ve got it all back together!
 

Dylpro

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May have spoken too soon. I don’t know how or why I was able to get it started last night, but haven’t been able to replicate it since.

However, after more digging for tips online I found some tests to run at the DIS module which showed 8.16V at pin 7, if I ground the wire to the intake or some form of metal the voltage drops and I can hear the injectors priming. It looks like someone has messed around with them in the past and the entire loom is a mess.

Not sure if I just had it in just the perfect spot for it to start last night or what, but I ordered a CMP just as a backup if nothing else. But almost certain there’s some kind of electrical issue in that region now
 

Dylpro

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She lives! It isn’t pretty, but after 2 months it started, ran, and stayed running. Repeat 5 times and called it a streak!

If I’m being honest, I don’t think I’ve “fixed” the problem, more so found a temporary solution, something that will at the very least get it out of the shop and back home.

Issue is something to do with the wiring to the DIS. Originally I had the wires draped over the top of the crossover, similar to the picture I’ve attached from before any disassembly.

After noticing voltage changes when grounding the shielded wires on either side I removed the crossover, tightened/replaced bolts to the DIS, and routed the wires to the proper position underneath the crossover. Lo and behold the car fires up and stays running.

That mess of wires still concerns me, but feels good to just have the car running again. Start ups are still rough as is the idling but assuming the spark plugs are once again fouled I’m planning on replacing them with a new set to see if it makes any difference.

Thanks again everyone!
 

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Irish Pride

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These bolts are grounds for the DIS. It's possible that you were having a grounding issue with those and just removing and reinstalling them could have fixed the problem. I've actually had that happen before. I had a no start situation after replacing the water pump. All I did was remove those two bolts and swapped them with each other and the car fired right up.

-Chad

20230120 092401
 

Dylpro

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These bolts are grounds for the DIS. It's possible that you were having a grounding issue with those and just removing and reinstalling them could have fixed the problem. I've actually had that happen before. I had a no start situation after replacing the water pump. All I did was remove those two bolts and swapped them with each other and the car fired right up.

-Chad

View attachment 86173
That would explain a lot. Every attempt up to the point where I was able to get it started I hadn’t had either of those brackets screwed down. The grounding issue seems to be resolved thankfully.

The streak was unfortunately broken when after 6 good starts in a row it couldn’t start. Figuring the plugs must’ve been completely fouled I put brand new plugs in and so far so good.

Unfortunately this car still needs a LOT of work so I have a feeling I’ll be popping in here quite frequently!

Thank you all again! And a huge thank you to Mike at SHO Source for providing a parts source for these cars. Couldn’t have done any of this without them!
 

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