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Been working on this issue now for a month or so and have no clue as to where to look next.
1988 S4 Auto with 46,000 miles.
I had recently completed a top end refresh - car ran great except for a random (not every time) no hot start. It was suggested that I send the MAF and LH out for refurb. Whilst they were away, I decided to remove the electrical panel, replaced the relays and clean up all the contacts. I re-installed the rebuilt LH and MAF and now the car is not running well at all. It has a pretty low idle as well as a really weird popping/sucking sound that comes and goes whilst idling as well as soon as I shut off the ignition. See the attached video. It is also misfireing/stuttering once it gets on the freeway. Speedtoys came over yesterday with his parts car and we switched over both the MAF and LH - neither of which made any difference. My MAF and LH worked just fine when installed on his car.
Everything new as follows
LH
MAF - Also replaced the 5 Pin connector
TPS
Temp2 - also a new connector
Idle Control Valve - not replaced but tested good with a 9V battery.
All New Gaskets on top end
Spark Plugs & Wires
Fuel Dampers and Regulator - only 5 years old and all hold vacuum
Would love to hear everyone's thoughts on the weird noise. Any Ideas ?
Start with the easy stuff. Verify that your spark plug leads are firmly seated and in the right order. Verify the coil wires seated at the bottom of the distributor and into the coils themselves.
get the WD out and run a test from the MAF connector to the respective pins on the computers.
make sure the ground wire bundles are connected and tight at the back of the V.
also test the connections to verify you have all of the connectors in the right location on the TPS and the crank sensor.
NOTE since it was running properly before you touched it it must be something you have done.
Right now be methodical look at every connection with suspicion till you have electrically tested it to the computer connectors
I've watched your video a few times.
At idle the engine is happy.
Check the manifold side cover seals. Spray some starter fluid near the manifold.
I suspect a vacuum leak - do you have access to a smoke tester?
get the WD out and run a test from the MAF connector to the respective pins on the computers.
make sure the ground wire bundles are connected and tight at the back of the V.
also test the connections to verify you have all of the connectors in the right location on the TPS and the crank sensor.
NOTE since it was running properly before you touched it it must be something you have done.
Right now be methodical look at every connection with suspicion till you have electrically tested it to the computer connectors
Sorry for my ignorance but was is a "WD"
Originally Posted by Kevin in Atlanta
I've watched your video a few times.
At idle the engine is happy.
Check the manifold side cover seals. Spray some starter fluid near the manifold.
I suspect a vacuum leak - do you have access to a smoke tester?
The side covers were not removed but I did remove one of the side cover Alan bolts so I could get to the fuel rail nut. I do have a smoke machine, so I will run that test in the morning and report back.
The thing that keeps coming back to me though is that it ran fine before I sent off the MAF and LH. Do you guys have any idea what could physically be causing that noise - is it a misfire or a no fire ? Just seems like a really odd sound - like something is flapping, either inside or around the intake.
Sorry for my ignorance but was is a "WD"
The side covers were not removed but I did remove one of the side cover Alan bolts so I could get to the fuel rail nut. I do have a smoke machine, so I will run that test in the morning and report back.
The thing that keeps coming back to me though is that it ran fine before I sent off the MAF and LH. Do you guys have any idea what could physically be causing that noise - is it a misfire or a no fire ? Just seems like a really odd sound - like something is flapping, either inside or around the intake.
I think it is backfiring through the MAF. You can see it at about 16sec in the video.
The sound you hear could be the backfire moving the throttle plate.
WD =wire diagram
check the plug wires and verfiy the timing marks
Checked plug wires and re checked all wires in the electrical panel - all checked ok
Originally Posted by Kevin in Atlanta
I've watched your video a few times.
At idle the engine is happy.
Check the manifold side cover seals. Spray some starter fluid near the manifold.
I suspect a vacuum leak - do you have access to a smoke tester?
Ran smoke test and only possible leak I could find was the throttle linkage.
I realize the only item I did not swap out with Jeff was the EZK - Any thoughts on if this could be the issue ?
Have you checked the connections at the ignition control units located under the plastic cover on the DS front panel (9 and 10 on the photo)? I don't think you can remove them from the panel with out destroying them due to the sticky adhesive material the factory used for heat sink purposes but you can check the connectors and swap the leads and see if anything changes. That might tell you if it is ignition related though vacuum leak would have been my first guess, too. Popping and backfiring is almost always timing related.
Problem Solved - A big thanks to Worf for helping figure this out. After several months of checking and re checking stuff - the problem was the Ground wire connection at the passenger side of the V - (Injector harness I believe)
I had loosened this up when i did the top end refresh at the beginning of the year. The car ran fine for at least a month or so after and I assumed all was good. The only issue I was having after the top end refresh, was an occasional no HOT start. Which is why I decided to send the MAF off. Though the car ran fine for that month or so, Im assuming the bolt must have worked loose over time - that along with pulling the MAF to send off was the final straw that caused the little to no contact.
Even though I know everyone says clean and check your grounds, I would never have thought it could cause this kind of issue. Lesson learned - CLEAN AND CHECK ALL GROUNDS - Thanks again Worf !
NOTE make sure to check the grounds at the back of the V after doing an intake refresh,
these wires have a high probability of being left loose on S4 machines.
NOTE the same applies to the 16V machines ,
check the wires on the right side cam tower for no corrosion and being tight.
When I encounter issues anymore, the very first thing I do is inspect any & all connections & associated wiring. It's the first thing I want off my list before I'll dive any further into diagnostics. Get into that habit & you'll be richly rewarded with so fewer frustrations.
Did you do any powder coat work while you were refreshing the top end? Post up some pics.
07-05-2024, 04:15 PM
'88 - Rough Running & Really Weird Noise
and we switched over both the MAF and LH - neither of which made any difference. My MAF and LH worked just fine when installed on his car.
