Help: Bucking under WOT at high RPM and random popping in the exhaust!?

91dak239

Registered User
So here is the scoop, i have a '92 SC the motor had a bad bearign in the bottom end, i got a good deal on an 89 SC with rebuilt motor but a bunch of other problems with the car, I swapped the 89 engine into the 92 using the 92's exhaust manifolds, wiring, and other bits from the 92' to make the engine work fine in the car.

So the engine more or less runs great except it randomly makes these popping noises that feel like they are coming from the mufflers!?

Under WOT at high RPM the engine bucks and i can visibly see the boost gauge bucking with it to some degree, this only happens at high rpms, i can give it good throttle lower rpms and it boosts and goes fine happens at about 4300-4500rpms+

I'm suspecting possible bad injectors or a DIS module!? The car has brand new; cam sensor, idle air control valve, throttle position sensor, plugs, wires and an accel coil pack.

Whats going on and any thoughts on direction to resolve these issues!? Many thanks in advance for the help.
 
So I drove the car around some more a bit ago, well the same problem that prompted the old engine to fail has just cropped itself back up again, its making a tick or a knock, its not as loud as the other engine was before it seems to have ultimately broken something in the bottom end, i parked the car imediately once i heard the noise again.

This engine ran fine when it was in the '89 SC it did not do this at all... The only thing it is using in the '92 is the 92's DIS module, and EEC. Everything else is from the '89 which was running perfectly fine when it was in that car. Could the DIS module be the culprit here??

Please help! I've been working to bring this car back from the dead for some time and it just wont come back, I'm at my witts end with the car, it has a new engine with new or known good working sensors with the exception of the DIS module which is carry over...
 
It could be the DIS module, but it's more likely because one of the plug wires is not seated on the plug, is damaged or one of the plugs has a cracked insulator.

David
 
I had a similar problem with a 90 I picked up in Tampa a couple months ago. I took it to a guy in Ocala, popping from the exhaust at idle and under moderate throttle. He fixed it by putting the correct plugs in it. (He told me the ones it had were for a non-supercharged 6 cyl.) Apparently the crank sensor was positioned such that it was making contact with something. He found this while checking to see if the H. Balancer was coming apart and squared that away. Next, he greased the area between the D.I.S. and A-C compressor bracket with what ever that stuff is. It now runs like a tired 'ol champ. The dealership couldn't figure any of this stuff out after three days so hang in there. The wide open throttle stuff kindof sounds like plugwires.
 
I'll have to check the plug wires and make sure they are nice and tight. They are brand new Taylor 8.2 mm wires. Its running Autolite 103's cant remember the gap but I got them based off a thread on here about spark plugs for the SCs. Should i put different plugs in the car? I'll check the plug wires asap make sure they are seated in properly.

Also I had accidentally carried over the '92s original PCV valve since the 89 had the wrong valve cover on it, seems quite possible the PCV is broken, but i don't know if it would cause this.

Could it be possible that the PCV is failed and letting the engine suck in copious amounts of oil causing a miss and or detonation? The '92's original engine had a fair bit of oil dripping out of the charge pipes, and the spark plugs were black. Where as the engine from the '89 didn't seem to have nearly as much oil in the pipes and the original plugs from that car were a redish color, which from what I found can be caused by fuel additives?

Also what should I put on the bottom of the DIS module? is it like grease grease, anti sieze, some kind of thermal compound?? I did take this off and put it back on the accy bracket.
 
Stuff between the D.I.S. and compressor bracket

I believe it's called heat sink compound. Help anyone?
 
DIS Interchange

I do have access to another DIS module from a 1995 For Taurus (3.0L engine) does anyone know if this happens to be interchangeable with the DIS Module for a 1992 SC?
 
Update

Ok so I worked some on the car, I've fixed the popping and presumable heavy load bucking. I did some more reasearch on here and found that I could use the '89s DIS Module, So I changed that and reinstalled it using a thermal grease used for PC CPU/Heat sink, this fixed the popping at idle and considerably lessened it under revs but it was still present. Then I decided to double check the plug wires and discovered I had accidentally flipped the # 4 and # 5 plug wires on the coil pack, the popping was completely gone after correcting that.

So that problem is more or less fixed. Now onto the reason I had to change the engine in the first place, the old engine made what sounds like a knock/ticking noise(it eventually got quite loud after 3 minor trips up the driveway and attempted diagnostics). Now this new engine was fine until it got to operating temps then the noise cropped up again, it did not make this noise when it was installed into the '89 at all.

I checked the PCV to make sure it wasn't broken and possibly letting too much oil into the engine, well that checked out as to be working properly. So I decided to check fuel pressure. It read 30PSI @ Idle, this sounds a little bit low to me and i swear i saw another thread on here saying it should be at about 38 PSI?? Is that correct and my fuel pressure is too low??
 
the 89 ecu wont directly swap out in the 92 ecu without some pin changes AFAIK


the wires on the coil from back to front left to right should be
1-2-3
5-6-4

if i had to guess i would say you have a bad coil, new or not, try the old 89 coil for ~~~~~ and grins

fuel pressure should be around 30 at idle thats perfect, disconnect the reference line on it and it will shoot up to 39

you sure your not hearing a transmission noise?

try replacing the oil with 5w20, DO NO USE FRAM FILTERS, anything but
 
Yeah coil/plug wires are all correct now. The popping in the exhaust has been totally cured.

The tick/knock ultimately resulted in a bearing failure in the original engine, thus why i changed it. This engine ran smoothly without this tick/knock noise when it was installed into the '89. When we were originally troubleshooting the car we tried using about 4 different coil packs none of which changed this tick or knock, so i highly doubt that the brand new Accel coil pack could be causing this... I'm almost certain that the noise is not from the transmission as well, both cars use the same M5R2 tranny, and I'm used to a pickup 5-speed which definitely makes some transmission noise and that's not what I'm hearing, maybe I'll try to get a video but this has me completely baffled!

All the sensors are either new or are from the '89 SC which again didn't seem to have this noise at all. its quite noticeable of a noise and isn't very difficult to hear. I think the only remaining items on the car that haven't been changed would be the EEC, MAF, Fuel Pump/Filter.

And if I didn't say it yet thank you all for providing me with some assistance, i really cant figure this issue out, I've done or tried everything i can think of..

Oh and the engine is currently running new 5w-30 Mobile 1 oil with a K&N Oil Filter
 
Well right now I seem to have basically ruled out everything but the EEC... Does this make any sense that the EEC could be causing the loud tick/knock noise???

The only thing i can think of is that the EEC is maybe not properly firing the fuel injectors and causing it to run extremely lean on some of the cylinders, causing detonation or something.
 
Well right now I seem to have basically ruled out everything but the EEC... Does this make any sense that the EEC could be causing the loud tick/knock noise???

The only thing i can think of is that the EEC is maybe not properly firing the fuel injectors and causing it to run extremely lean on some of the cylinders, causing detonation or something.

The EEC isn't likely to cause a tick/knock noise, it's almost always a mechanical issue. Have you isolated what portion of the motor the noise is coming from ? Does the noise get better or worse when motor warms up ? Does it change with RPM ? Check engine lights ?

Most common cause of sounds like that are from an exhaust leak at the manifold or incorrectly adjusted rockers. It may just need some thicker motor oil.

David
 
Well right after I put the engine in the car it was fine and didn't make the noise, then the noise started up after it got to operating temps for about the second time, I immediately babied the car back home as soon as I heard the noise crop up, now the noise seems to be present with the engine cold its not horrendously loud but its noticeable.

What weight oil should I try? It rarely drops below 32F here so i think i could get away with like a 15w-40 or maybe even thicker. Its pretty easy to just drain the oil and put something else in.

I hope something in the car isn't killing engines left and right cause this one was fresh and run good before being in this car :(

Edit: Forgot to answer some of the questions
It does increase in speed with the RPMs and there are no CEL or codes. I double checked all the exhaust connections an re-torqued the ones i could get to and they seem to be good...
 
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Hook up a mechanical oil pressure gauge and see what pressure you are getting on cold starts and at warm idle. Should be 80-90 psi cold and 35-40 at idle with motor up to operating temp. I'm using 10-40 in the winter and 15-40 in the summer.

David
 
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