Fuel injection

Tiny
THOMAS ESTABROOKS
  • MEMBER
  • 1998 CHRYSLER TOWN AND COUNTRY
  • 3.8L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 213,555 MILES
I have a feeling that my fuel injectors are probably clogged in this vehicle. A couple of people told me they can be taken out and cleaned with a needle or something very small like that. And then they can be reused. My question is is this true or do I need to replace them?
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Tuesday, June 28th, 2016 AT 1:59 PM

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Tiny
CARADIODOC
  • EXPERT
No on all accounts. What is the symptom or problem you are trying to solve?
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Tuesday, June 28th, 2016 AT 3:17 PM
Tiny
THOMAS ESTABROOKS
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I do not know if you got my last reply. The engine is running kind of rough. Plugs, plug wires and the coil have been changed are all brand new.
I was also told that sea foam a product you can get and put in your tank will unclog the injectors is this true or is this harmful?
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Wednesday, June 29th, 2016 AT 2:32 PM
Tiny
CARADIODOC
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I have never used Sea Foam but I have heard good things about it from other people. First of all, injectors are sealed and they're not take-apart-able. If you could get one apart, the clearance between the pintle valve is measured in millionths of an inch, so just handling the parts could cause it to stick or not seal properly.

GM has a problem caused by them just grabbing a handful of injectors from a large bin on the assembly line, then they stuff them into the engine with no regard to matching them. When they get a 100,000 miles on them, there is enough wear that they flow different volumes of fuel. One or two cylinders will run leaner than the rest, and the oxygen sensors will detect the excessive unburned oxygen in the exhaust. The lean condition can result in a barely-noticeable misfire, but the Engine Computer will detect it. Both of those conditions will set diagnostic fault codes and both codes will turn on the Check Engine light, but to the driver the engine seems to run fine. The fix is to replace all the injectors with a matched set of rebuilt injectors.

Chrysler has never had that problem because they buy their injectors from Bosch in flow-matched sets. Besides that, injector problems are unheard of, and that's why I'm doubting your diagnosis. There is a pickup screen in the gas tank, and there is a fuel filter after that. Other than for diesel engines, you will never solve a running problem on a Chrysler product by replacing the fuel filter. They easily last the life of the vehicle unless they rust out and start to leak. They do a real good job of filtering out dirt and debris.

All of the gas you buy today has way better additives than it had even twenty years ago, so you are not going to get any type of sludge or slime at the injectors. The injectors have extremely fine screens to stop particles from reaching the pintle valve. The only particles that could be there have to come from after the filter. That means pieces breaking off the rubber fuel hoses, and there is only a 3"-long piece at the filter, and a 12" piece between the body and the engine. If a hose is that deteriorated, it is going to leaking soon. Those particles, if they did exist and collect on the injectors' screens, would be much too few to block fuel flow, and no chemical is going to get rid of that. You do not want anything in there that is going to dissolve that rubber because it would also dissolve the insulating varnish on the coil of wire in each injector, and it would dissolve the hoses. Remember that millionths of an inch clearance issue too. Anything other than gasoline going alongside that valve could get stuck and prevent the valve from moving or it could get stuck at the orifice and hold the valve open so fuel won't stop flowing.

There are machines for cleaning fuel systems. Most of them require the vehicle's fuel pump to be disabled, then the engine is run for about twenty minutes on a pressurized can of strong detergent that is attached to the fuel system test port. Some people swear their engines run smoother after that service, but most of them drive Fords and GM products. I worked for a very nice family-owned Chrysler dealership for ten years, and we never even had a fuel system cleaning machine in the shop. There was no need for it.

In all the years I was there, through 1999, I only replaced one set of injectors, but I do not remember why. There was a recall, and we were supposed to check the color of them. If they were black, as I recall, we were supposed to install green ones. If they were green, the customer could go on their merry way. Other than that one car, we did not even stock injectors in the parts department.

For your symptom of running rough, that is open to interpretation. A collapsed engine mount is fairly common, and if the two metal brackets are no longer being separated by the rubber isolator, normal engine vibration can be transmitted into the body where you can feel it. If the engine is really misfiring, that will be detected by the Engine Computer. It will set a diagnostic fault code, and since that could adversely affect emissions, it will turn on the check engine light. You feel a misfire because the rotational speed of the crankshaft slows down due to that missing power pulse, and that momentary reduction in speed is what the computer detects.

Your mechanic can also perform a cylinder balance test to see if one is down on power. We used to short out a spark plug, then watch how many rpm the engine slowed down. Ideally each cylinder caused an equal rpm drop. On your engine an idle speed motor is run by the Engine Computer to maintain the desired idle speed. (As a point of interest, the instructor at a Jeep school disabled six cylinders on a V-8 engine. Obviously it ran very poorly on only two cylinders, but the idle speed will still correct. That shows how much control the computer has with that idle speed motor). That motor is not a motor as we think of a spinning armature. It is a "stepper" motor with an armature that is pulsed to a specific position through varying and alternating magnetic coils. As it rotates, it turns a threaded rod that retracts an air bypass valve to let more air in. At the same time it varies the length of time it holds the injectors open during each pulse. The point of this story is there are 256 imaginary "steps" that armature can be pulsed to between fully-closed and fully-open. For a properly-running engine, step 32 is typical of what we would see listed on the "sensor data" screen on a scanner. With a single cylinder totally misfiring and contributing no power at all, step 50 is typical. We look at the step number to determine where to start looking for problems. If idle speed is too low, and it's on step 20, we'd expect it to be too low. Now we have to figure out why it is asking for such a low idle speed. If we see step 65 and idle speed is too low, the computer is trying to get idle speed back up to where it should be, but it isn't having the desired results.

In your case, if there is a misfire, I would expect to see idle speed is correct, but the number of steps is abnormally high to get that idle speed there. Potential causes are an EGR valve that is stuck open due to carbon buildup. That valve should never be open at idle or low speeds because we would feel it. A cylinder could be down on compression due to a burned valve. A lobe on the camshaft could be worn so a valve isn't opening far enough. Those last two things are very uncommon.

A mechanic who specializes in engine performance issues will use an exhaust gas analyzer to help with the diagnosis. A misfire due to a spark-related problem will result in excessive unburned fuel and air going into the exhaust system. You'll smell the unburned fuel at the tail pipe, but the front oxygen sensor will detect the unburned oxygen as a lean condition. A fault code should set for that.

Low fuel pressure can cause rough running too, but there are things to consider. First, when Chrysler fuel pumps fail, they almost always fail to start up when you try to start the engine. That leaves you sitting in the driveway. GM fuel pump, by contrast, most commonly fail while you are already driving, leaving you stranded on the side of the road. GM pumps are also known for running too slowly, and therefore not building sufficient pressure. That is aggravated by the fact that many of their engines will not run at all if fuel pressure is just a few pounds lower than the required 45 to 60 pounds.

When I was chasing an elusive intermittent problem on my 1988 Grand Caravan, normal fuel pressure was 50 psi, but the engine ran perfectly all the way down to 20 psi, and the first symptom of surging showed up at 15 psi. The only way I could force that problem to act up was when pulling a tandem axle enclosed trailer that is bigger than the van! The fix turned out to be to replace the plugged screen in the gas tank. $12.00 for the part and about an hour on the hoist.

So there is my story. Check fuel pressure. Check for diagnostic fault codes even if the Check Engine light is not on. Perform a cylinder balance test if you think the fuel system is involved, but you will need a scanner to view the "idle speed motor steps".

Many scanners also have a misfire counter, but that varies between scanners and car brands. Certain conditions must be met, and there must be a minimum number of misfires within a specific period of time for a misfire fault code to set. You may be able to view a misfire counter even though no code has been set yet. If there is a misfire, the computer will know which cylinder is causing it. Start by swapping its spark plug and wire with those from another cylinder. Erase any fault codes, drive the van, then watch to see if the same code sets for the same cylinder or for the cylinder you moved the parts to.

You can also swap injectors the same way, but I would be real surprised if that changes the cylinder a misfire has been detected for.

Next, you might suspect the MAP sensor. All other car brands use a mass air flow sensor as their main fuel metering calculation. Only Chrysler has been able to make an engine run right consistently without one. On their engines, the MAP sensor has the biggest say in how much fuel is needed. It develops a signal voltage that varies between approximately 0.5 and 4.5 volts. If a defect develops that causes it to generate 0.0 volts or 5.0 volts, that is what triggers one type of fault code related to that sensor. The problem is a sensor that is starting to fail can generate the wrong signal voltage, but as long as it's within that acceptable range, no fault code will be set. There are other defects with it than set other fault codes, but a tenth of a volt change results in a big change in the amount of fuel requested, so that tiny error can cause hard-to-diagnose problems. GM had a huge problem with their MAP sensors in the late 1980's, so they sold them to Chrysler. It is no surprise then that Chrysler had a huge problem too. Those days are gone. GM redesigned them and now they give very little trouble. It is more common to find a vacuum leak in the hose going to the sensor, (by the way, this sensor measures intake manifold vacuum and barometric pressure). That leak makes the sensor see lower vacuum which it equates with accelerating and / or load on the engine, and the need for more fuel. To address that possibility, starting in the mid 1990's they began using MAP sensors with a vacuum port that plugs right into the manifold. There is no hose to leak,

Beyond all this wondrous wisdom I've shared, an engine performance specialist will look at the sensor data on the scanner to see what doesn't look right. There is always a long list of conditions for a fault code to be set for a detected defect, and that list always includes that certain other codes can't already be set. That's because many things are detected by comparing two or more of them to each other. If the computer knows it cannot trust the readings from one sensor, it will suspend any tests it uses that sensor for to compare other things to.
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Wednesday, June 29th, 2016 AT 11:19 PM

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