Engine Unexplainable Exhaust Pop and Gurgle

[Mrnissen122]

Gentlemen, I need some assistance from those wiser than me. I have a 1989 Ford Mustang LX, it was originally a 2.3L auto which in my younger, poorer, impulsive, and more stubborn years I Frankenstein-ed this thing over to a 5.0L.

The vehicle has an old 1986 Thunderbird 5.0L non-HO (still has the non-HO firing order, in my youth I just re-arranged the pins to the ECM to get the injectors to fire correctly. Worked great after doing that.), CAI, 30lb injectors with calibrated MAF, off road downpipes and dumps by the rear wheels with glass pack mufflers, EGR delete kit, and a MSD ignition coil and distributor. Up until this point I had no issues with drivability, it just simply didn't have the HP because it was getting choked out with its restricted top end.

I recently made the decision to come back to the car after taking a break with it for a few years. Started it up, ran fine so I went ahead and bought Trick Flow Twisted Wedge 170cc heads with a 61cc chamber, a Trick Flow Track Heat Intake Manifold with 1" spacer, a 70mm BBK throttle body and spacer, and a set of equal length shorty headers. Put that all together started it up, ran great at idle. Took it for a drive and the very first thing I noticed was that I had a HORRIBLE exhaust noise after it warmed up. It happens at highway speeds, lower residential speeds, accelerating, coming off the gas, etc. Not so much between idle to roughly 30 mph. It was popping, gurgling, the works. Embarrassing to drive. Took it back home and I felt some exhaust pushing out around the headers. Fixed that thinking I found my problem, and no change.

Could it be that its running rich or lean with the changes made? It had no issues before and I have ensured my fuel pressure and timing is accurate. With it breathing better now could that be causing a secondary ignition in my exhaust or simply a leak further down the exhaust that I missed? Hard to believe its one of those considering I had no issues prior with the older more stock set up. Am I overlooking a vacuum leak? Could that really cause all this guff? Am I missing something else? Your help is appreciated!!!

 

[JD1964]

If its popping in the exhaust it could be ignition related. Even as simple as one bad spark plug or plug wire. A plug or wire with excessive resistance might cause cross fire in the distributor or between ignition wires. When that happens you will get one cylinder thats not firing along with another cylinder thats firing out of time. The cylinder thats firing out of time is where the popping might come from.

 

[AeroCoupe]

Have you checked for codes? Being you have an 89 it does have a check engine light (CEL). It will flash when codes are present but only emissions related codes. This means there can be non emissions related codes present.

 

[Noobz347]

I recently made the decision to come back to the car after taking a break with it for a few years. Started it up, ran fine so I went ahead and bought Trick Flow Twisted Wedge 170cc heads with a 61cc chamber, a Trick Flow Track Heat Intake Manifold with 1" spacer, a 70mm BBK throttle body and spacer, and a set of equal length shorty headers. Put that all together started it up, ran great at idle. Took it for a drive and the very first thing I noticed was that I had a HORRIBLE exhaust noise after it warmed up. It happens at highway speeds, lower residential speeds, accelerating, coming off the gas, etc. Not so much between idle to roughly 30 mph. It was popping, gurgling, the works. Embarrassing to drive. Took it back home and I felt some exhaust pushing out around the headers. Fixed that thinking I found my problem, and no change.

All of this with what ECU and what method of tune?

There is [no portion] of the stock, Speed Density ECU that will support these mods. I am a bit surprised this combination has not already grenaded. If you continue to try and drive it this way, it [will] cause damage if that has not occurred already.

 

[86HO5.0]

He's running MAF with 30lb injectors.

x2 on codes and method of tune.

With all of those mods a wideband would be a very good idea.

 

[Mustang5L5]

With no video to hear the sound, my assumption is you are running rich and what you are hearing is the excess fuel lighting off inside the exhaust. How are you tuning the vehicle? Just relying on the calibrated MAF? Are you 100% sure it's the right MAF for 30's?

 

[GOvert]

I 2nd the advice on installing a quality brand wideband gauge and o2 sensor kit. With all of the changes that have occurred, it would be nice to see what is going on with the air/fuel mix. But of course, the ignition miss/es or in some cases, the exhaust leak would need fixed first.

 

[Noobz347]

I might try installing the OEM MAF and a set 19 lb injectors and see how it runs.

Trick Flow Twisted Wedge 170cc heads with a 61cc chamber, a Trick Flow Track Heat Intake Manifold with 1" spacer, a 70mm BBK throttle body and spacer, and a set of equal length shorty headers.

If this is the total of current mods, it should run just fine with 19s. If it runs well, you can then start looking around for a MAF that flows better and matches your other inlet mods.

 

[Mustang5L5]

I might try installing the OEM MAF and a set 19 lb injectors and see how it runs.

For the sake of troubleshooting, it will run fine. Just don't do any sustained WOT pulls. But for general cruising, I never had issue maintaining a good AF ratio when i used 19s on my TFS170 headed combo. Light rolling on the gas, a quick roll out, never had an A/F issues doing things like that. Just don't get temped to go hammer down.

If the OP is up to it, a swap back to 19's and the stock MAF might help rule that out.

However, I am making assumptions here based on the description of the noise. A video would be helpful as this could also be any other number of causes. It could be something as simple as two of the injectors are swapped, considering the OP rewired the injector harness to run a non-HO cam on a HO firing order. In fact..this would be my first suspicion that something is not right here.

 

[86HO5.0]

Agreed on the no sustained WOT pulls, 19's aren't enough for that combo.

 

[2000xp8]

I think first we need to establish what a 1986 non HO Tbird engine really was.
A few searches yielded a few different answers, was it a roller cam? Flat top piston low compression engine?
Looks like the hp may have been 150hp from the factory?
If the answers are yes, everything I see suggests that engine was not the greatest.
No way in hell he's exceeding 19lb injectors, he would have to more than double the engines rwhp.
You can get close to 300rwhp with 19's, it's stretching it, but it's been done before.
Without an aftermarket cam, even in a newer engine 19's would most likely work.
My point is, 30's may very well be drastically off.

 

[AeroCoupe]

1986 non-HO 302 is a roller motor with a flat tappet cam hence the old 302W firing order and not the 351W firing order. That motor should have been right at 9:1 on compression and I believe easily converted to a roller cam being the block is actually a roller block. Basically everything from the heads up is recycle bin material including the camshaft. Pistons are flat tops but have no valve reliefs so think 85/86 Mustang 5.0.

I ran 42 lb/hr injectors on a mild 302 and they worked just fine with a tune. Typically 30 lb/hr injectors on a "calibrated" MAF like a Pro-M are just fine but anything past that is starts to get hit and miss.

 

[Noobz347]

Typically 30 lb/hr injectors on a "calibrated" MAF like a Pro-M are just fine but anything past that is starts to get hit and miss.

I have seen a lot more misses at the 30 lb injector point than I have successes. In the old days, we'd make up for a lot of that with an adjustable Fuel Pressure Regulator.

It needs a tune. Telling the EEC that there is less air flowing than what the OEM meter tells it, is a "trick" and not so much a fix. Sometimes it works out. What it cannot account for are the physical differences between the injectors. A 30 lb injector for instance, will ramp up [way] faster than a 19. That makes it fat as fook while it is in transition. That also means that WOT pulls will be [the] worst part. The EEC is ramping that 30 lb up during accel like it's a 19 lb injector. That will be a "nope".

Swapping in an OEM meter and injectors (even temporarily) will tell the story.


I've run a lot power through 19s and an FPR. I think it'll take a set of heads and stock cam without much issue.

Back the topic of the "calibrated MAF". With today's digital tuning, these are obsolete. The MAF is skewed to accommodate the A9L and A9P (sometimes the Cobra EECs too). In order to do this, the resolution of the MAF itself has to be truncated to try and adapt for whatever injector you're using. The bigger the injector, the more skewing of the MAF. So, you're truncating that 0 to 5 volt range used to signal the EEC. You're [losing] MAF resolution.



These days, it is far better to get a MAF that uses the [entire] range and get the thing tuned.

The 30's by themselves are not the issue. With tune and a good MAF it would run just as good with 100 lb/hr injectors.