About to run my '87 Carrera off a cliff - still surging and backfiring

[Mia911]

Originally Posted by ivangene

I have a big curb out front...if that works you both can drop those cars over it and I will be glad to catch them at the bottom for you to "help out"

Lmao....

[DRACO A5OG]

Originally Posted by Tippy

Yeah, I need and LMX!

The chip has been in there for about 4 years.

I used a whole can of starting fluid and if has vacuum running through it, I sprayed it with NO change to RPM.

I still wonder if the brake booster diaphram could be leaking......

Smoker will find a leak, if it exists.

[ischmitz]

Tippy, I responded to your PM. Let me just touch some points here:

You need to check your mixture (don't mess with the adjustments without having proper test equipment). If it is out find the reason for it. The chip is an unknown as others pointed out. However most chip tuners only mess with WOT maps so it not the likely root cause. But to be sure you either need to read it and compare it to stock or swap it out to a stock one.

If you are too rich, you could have leaking injectors, bad fuel pressure, or an open CHT, or a bad DME (sensor input damaged)

One thing many overlook is the fuel pressure regulator. If the vacuum line to it is damaged or the regulator is blown you might run at max. fuel pressure resulting in a rich condition at part throttle. As a quick test pull the vacuum line with the engine idling. It should make a difference (go rich). If not you have an issue with the FPR.

Hope that helps,
Ingo

[Tippy]

Originally Posted by ischmitz

Tippy, I responded to your PM. Let me just touch some points here:

You need to check your mixture (don't mess with the adjustments without having proper test equipment). If it is out find the reason for it. The chip is an unknown as others pointed out. However most chip tuners only mess with WOT maps so it not the likely root cause. But to be sure you either need to read it and compare it to stock or swap it out to a stock one.

If you are too rich, you could have leaking injectors, bad fuel pressure, or an open CHT, or a bad DME (sensor input damaged)

One thing many overlook is the fuel pressure regulator. If the vacuum line to it is damaged or the regulator is blown you might run at max. fuel pressure resulting in a rich condition at part throttle. As a quick test pull the vacuum line with the engine idling. It should make a difference (go rich). If not you have an issue with the FPR.

Hope that helps,
Ingo

Good point about not messing with the parameters without AFR's.

Injectors are relatively new, fuel pressure seems to be ok (I have a fuel pressure gauge in the cabin), the CHT checks out good, along with all the other sensors checking good according to the manual.

I am going to check the FPR as Todd pointed out too and see how it reacts.

Thanks!

[ischmitz]

The other thing I didn't pick up on is the fact that you run a turbo setup. That is obviously not stock and I will affect your mixture.

When a turbo is added to a stock 3.2 there are many ways this can be done. In its simplest form you modify the chip, add a blow-off valve and the turbo. Then screw with injectors/fuel pressure and FPR and hope for the best. However, the barn-door AFM cannot differentiate between an intake charge under pressure (boost) and a N/A intake charge. The dilemma is that you have to protect the engine. So you need to increase the amount of fuel because you get more air into the cylinder if the charge is compressed. As a consequence without boost the mixture will be overly rich.

If yours is a bolt-on solution, I assume modified maps and a modified fuel pressure regulator are used to richen the mixture. This is so when boost kicks in it doesn't ping. The DME doesn’t see whether the engine is under boost or not. So it always delivers the increased fuel (due to FPR and map changes). This could cause your bucking.

[Tippy]

The setup it has, has ran flawlessly for 5+ years. And yes, it has a chip, rising rate FPR, big injectors, and dual -044 pumps. All else is factory FI components.

I unplugged the high-altitude switch and no change. Stills runs like crap right off idle.

Fuel pressure is running at 2.8 bar at idle and jumps quick if you stomp the throttle. What I'm not seeing is a bump in pressure if I quickly, slightly crack open the throttle. Only with large openings will the pressure jump.

Wonder if this normal?

[Tippy]

Hmmmm.......I just read the workshop manual.

It says these are the readings for fuel pressure:

Engine off: 2.5 Bar -------- I'm getting ~3.05 Bar
Engine running: 2.0 Bar -------- I'm getting ~2.8 Bar

I have HUGE injectors which may make it even richer, but I don't know what the chip has programmed.

The other problem is I have never hooked up the fuel pressure gauge until this happened to see what it always ran at before.

[ischmitz]

...and this is the stock FPR or a fancy aftermarket version?

[Tippy]

Originally Posted by ischmitz

...and this is the stock FPR or a fancy aftermarket version?

Protomotive rising-rate FPR

[ischmitz]

So Promotive should have the specifications and maybe even a test procedure for their FPR. I would ask them what the expected pressure values are.

BTW, not sure what "rising-rate" means. The stock fuel pressure regulator uses the manifold air pressure to adjust the fuel pressure.

[Tippy]

It runs off boost to create the additional fuel. It pegs the gauge north of 5 bar under boost.

[ischmitz]

ok, so that is to protect the engine from detonation under boost. Loads of fuel.....

With larger injectors and higher fuel pressure you will run richer than stock at idle. Not much the DME can do about it and here is why: An injector has a minimum pulse length on the order of about 1mS. That is the lowest flow rate. Below that the injector doesn't open and the engine stops. The minimum opening time X multiplied by injector flow rate is the amount of fuel the engine is getting. And the flow rate is directly proportional to the idle fuel pressure.

With your setup I would have expected slighly lower fuel pressure at idle compared to the stock regulator to compensate for the larger injectors. But your FP is higher. That doesn't make sense.

Ask Promotive about the specs.

Ingo

[Tippy]

Makes sense, I thought the pulse-width may be really short requiring higher pressure.

I definitely need to call Protomotve.

[MotoSook]

Now I see it's turbo'd.

The injectors, chip and FPR need to match. Are they? Or did you piece the system together? We had a Promotive system on a 3.2 and it worked just fine with stock and 52 lb injectors (with the right program).

The whole thing has to be designed/programmed to work together, incl boost pressure.

Is the FPR plumbed correctly? Are you boosting your brake booster?

[fbarrett]

Start with the basics. Is the gasoline fresh? I just went through this with a backfiring and rough-running carbed car that was acting up. Drained the old gas, filled it with fresh and a can of BG44K, and the problem was solved. The "gas" we get these days is crap.

Frank

[Tippy]

Originally Posted by Soukus

Now I see it's turbo'd.

The injectors, chip and FPR need to match. Are they? Or did you piece the system together? We had a Promotive system on a 3.2 and it worked just fine with stock and 52 lb injectors (with the right program).

The whole thing has to be designed/programmed to work together, incl boost pressure.

Is the FPR plumbed correctly? Are you boosting your brake booster?

The entire system has been in this configuration for 5+ years. Yes, I am boosting the brake booster but I have already choked off the hose and saw no difference.

Originally Posted by fbarrett

Start with the basics. Is the gasoline fresh? I just went through this with a backfiring and rough-running carbed car that was acting up. Drained the old gas, filled it with fresh and a can of BG44K, and the problem was solved. The "gas" we get these days is crap.

Frank

Gasoline is fresh - 93 octane normally from Chevron.

[kodioneill]

Where did you choke off the hose to the booster? At the booster or in the engine compartment?

[Tippy]

Right before the throttle body

[Tippy]

Another question:

Assume all sensors, harnesses, and mechanicals of engine are within spec.

Is there anything in the DME that can cause the rich/lean condition I have or intermittent cutout of spark?

[slw911SC]

Sounds more fuel related than electric. Simple stuff, maybe, like: dirty tank, bad fuel pump, clogged fuel filter (always a culprit), faulty fuel regulator, faulty fuel distributor, injectors/ seals, clogged fuel lines, hoses, mixtures, etc. All pretty easy stuff to check. Good luck!