Fuel Injector Problems

(This is an internal page of the JAGUAR FUEL INJECTOR SERVICE.com website)



The fuel injector, though small, is a very solidly constructed fuel system component part.  It has to be, considering the extreme heat environment where the injector is located.  As mentioned on another page of this site, for a daily driver vehicle, (12,000miles/year), each injector will cycle approximately  18,000,000 times annually !!   Recall, that the Jaguar V12 HE injector fires twice per engine cycle.  So that at 2,000 RPM, the injector has operated 2,000 times.  That's 33.3 times/second.   An extraordinary duty demand indeed!  If you consider your personal vehicle, and your driving habits, you can get an estimate of the service duty thru which they have been subjected.

Due to the heat environment, the extraordinary duty demands, and the fact that, after all, the fuel injector is a mechanical and electrical part, the fact is, an injector is subject to problems, faults and failure.  Let's take a look at the potential fuel injector problems and failure modes of an injector, the possible causes of each failure mode, and the potential resulting effect on engine performance.


INJECTOR FAILURE 1...Unburned fuel additives are baked on the injector pintle and orifice altering flow volume, altering fuel spray pattern.

CAUSE OF FAILURE 1...normal use of vehicle but lack of fuel system maintenance;  after engine shutdown "heatsink" resulting in higher "baking" temperatures for unburned fuel and/or fuel additives remaining on injector;  overheating of engine (and the injectors) from faulty cooling system, improper engine timing, contaminated fuel, incorrect fuel octane, vacuum leaks.

EFFECTS OF FAILURE 1...reduced engine power, sluggish pickup/performance, reduction of fuel econony, leaking fuel injector, potential for engine overheating, O2 sensor damage, remaining injectors/cylinders are overfueled to compensate for underfueled injectors/cylinders as the "closed loop" O2 system attempts to maintain stoiciometric ratio.


INJECTOR FAILURE 2...Injector filters become clogged.

CAUSE OF FAILURE 2..."Foreign particles" in fuel tank(s) or fuel lines, or fuel rail.  Foreign particles in almost all instances, will be rust. Larger rust particles may be collected within the injector filter,  or the fuel filter, and reduce fuel flow.   Microscopic rust particles may also pass thru the injector filter, and cause the spray pattern to alter, fuel flow to alter, and/or the injector pintle to not seat properly.  This is a common problem on vehicles that have sat unattended, or suffered from lack of routine maintenance.  Incorrect fuel tank fuel filter; holes/tears in fuel tank fuel filter; breakdown/degradation of interior wall of fuel supply line; breakdown/degradation of interior wall of fuel injector hose, and rust in the fuel rail.

EFFECTS OF FAILURE 2...the injectors leak at the pintle and/or the spray pattern is altered, and/or the fuel flow is altered.  Lack of engine power from underfueling; potential for engine overheating; remaining injectors/cylinders are overfueled to compensate for underfueled injectors/cylinders as the "closed loop" O2 system attempts to maintain stoiciometric ratio.


INJECTOR FAILURE 3...Injector windings don't lift pintle, seized pintle, or slow pintle cycling.

CAUSE OF FAILURE 3...injector coil windings overheated from cooling system failure or ignition failure, with windings losing their magnetic performance; open (broken) windings; shorted (grounded) windings; seized pintle from internal injector corrosion (engine has set too long without running causing the injector to rust internally, petrol contamination with water, or cycling of injector without fuel flow to act as cooling agent and lubricant).

EFFECTS OF FAILURE 3...(A) If injector pintle is "off" the seat...overfueling of affected cylinder with resultant underfueling of remaining cylinders within "closed loop",  poor engine performance, poor fuel economy, possible O2 sensor damage, potential engine overheating and engine damage, hard or no start, fuel leaks after shutdown.   (B)  If injector pintle is "on" the seat...underfueling/no fueling of affected cylinder and possibility of  a non-firing cylinder, with resultant overfueling of remaining cylinders with "closed loop" system, poor engine performance, poor fuel economy, O2 sensor damage, engine/piston/ring damage.


INJECTOR FAILURE 4...Body or mechanical joint leak in injector body.

CAUSE OF FAILURE 4...Defective manufacturing and testing, overheating of injector from cooling system failure, ignition system failure, incorrect timing, improper "handling" during installation/removal/storage/shipping, etc.

EFFECT OF FAILURE 4...High potential for engine fuel fire (dependent on location of leak), poor engine performance, poor fuel economy, potential for engine damage.


INJECTOR FAILURE 5...injector pintle doesn't fully seat on orifice.

CAUSE OF FAILURE 5...fuel additives "baked" on pintle or orifice, weak injector return spring, rust/corrosion internal to injector body.

EFFECT OF FAILURE 5...leaking fuel injector, after shutdown fuel leak in affected cylinder (causing hard start), overfueling of affected cylinder with resultant underfueling of remaining cylinders in the "closed loop" system,  potential for damage to O2 sensor or "cats".


INJECTOR FAILURE 6...external electrical connectors broke/corroded.

CAUSE OF FAILURE 6...mishandling during installation/removal/testing, water/moisture leaking past injector plug connector, inadequate vehicle maintenance, improper storage.

EFFECTS OF FAILURE 6...no firing, intermittant firing, or weak firing of injector due to poor electrical conductivity , poor engine performance, poor fuel economy. engine overheating, potential engine damage, overfueling of other cylinders  as 02 sensor  reads excess 02 in exhaust and adjusts "rich" to compensate.


"CLOSED LOOP" SYSTEM note...When the engine management system is in this mode, the 02 sensor(s) are monitoring O2 exhaust gas emissions and feeding signals to the ECU.  The ECU will interpret the signal(s) and adjust injector "pulse width", within a range, attempting to keep the air/fuel mixture at the proper ratio, such that O2 (and therefor exhaust emission levels) are within specifications.  Some engine failure conditions cannot be fully compensated for and the engine will remain in a "less than satisfactory" level of performance.  If the ECU can return the air/fuel ratio back to a "satisfactory" level, it must be remembered that there is still a failure condition present, which required correction.  The ECU has merely "balanced" out by overfueling or underfueling cylinders (injectors), to achieve an acceptable exhaust emission reading.  Fuel consumption will still be higher than spec, and performance will still be low.

"OPEN LOOP" SYSTEM note....This is repeated elsewhere on the site due to its importance!  In "open loop" operation, the ECU is not monitoring the presence of O2 in the exhaust stream.  The engine goes "open loop" at WOT (wide open throttle) and the ECU fuel adjustment goes rich  +/- 10 %.  This keeps HP up, and engine temperatures down.  Injector flows that may have been  adjusted for low flows in "closed loop", will STILL remain underflow...even with the WOT fuel addition.  Not a good situation at WOT.

Fuel injectors are made to operate thru several billion cycles.  Rarely do they fail mechanically or electrically.  The most common failure mode is...they get fouled from burned on fuel and fuel additives, causing poor spray pattern, poor atomization, poor vaporization of fuel if the fuel does not hit the "target zone" on the back of the intake valve, and reduction in fuel delivery.  The ECU can be compared to the human brain...the ECU does the thinking, signaling the injector on when to fire, and how long the pulse duration should be. The fuel injector can be compared to the heart...the injector does the pumping. It has no brain and only responds based upon ECU input.  If an injector, or injectors, are not on spec,  the ECU will attempt to correct flow delivery via altering injector pulse, but it cannot correct the faulty injector(s).   Injectors need to be clean for optimal system performance.  


(relevant reading)


Fuel injectors are manufactured to spray fuel in a direction that is parallel to a line from the centerline of the filter bore (at the top of the injector) to the centerline of the injector pintle (at the lower end of the injector).  That is, the fuel spray pattern should leave the pintle end of the injector as though it was fired from a gun...in a straight line.  (Forget about trajectory angles...think straight line.)  In doing so, the fuel spray hits its designed target at the exact target location on the back side of the intake valve.  The engineering designed effect is to vaporize the fuel that has been atomized by the injector, by fuel hitting the hot intake valve.  Recall, that the greater the atomization of the fuel, the smaller the diameter of the fuel droplet, therefor...the smaller is the overall fuel droplet surface area,  and the fuel droplet approaches the ideal size to be totally burned, as it mixes with the available air intake. If the fuel droplet does not reach a size, such that it is totally burned, then the unburned portion is exhausted .  It is not uncommon for clogged injectors to have an off-angled spray direction by 5 percent.  While this may not seem to be a large degree of error, consider the following.  On a 1984 XJS V-12 HE, the distance from the pintle seat of the injector to the back side of the intake valve is approximately 4 7/8".  If the injector spray angle is off by 5%, then the fuel spray misses the target location by 15/32"  ( almost 1/2" ).  Depending on the direction of the off-angled spray, the fuel will either hit the intake valve stem,  the outer lip of the intake valve, or in more severe cases, the wall of the intake.  Furthermore, if the injector is fitted with a lower seal ...(a seal between the injector and the intake manifold), and that seal has become deteriorated, or collapsed from age, engine heat, or both, then there is a probability of the injector fitting in the intake at an off-angle, which may produce the same off-angled spray pattern effect, or exacerbate an already off-angled spray pattern, as well as the probability of an air leak.  The result, in all cases above is ... fuel wetting or (puddling) on the valve stem or the intake manifold wall ... a decrease in fuel droplet surface area... a decrease of fuel vaporization... ... a decrease in total fuel burn  ... a loss of HP ... a decrease in fuel economy  ... and reduced performance.   Does an off angled spray pattern matter?  Yes.  Will dirty injectors or deteriorated seals cause off angled spray patterns?  Yes.  Is it important to have clean, and maintained injectors?  You decide.


Atomization of fuel VS. Vaporization of fuel.


The fuel injector atomizes fuel.  It physically turns liquid fuel within the fuel rail into tiny droplets of fuel, and injects that stream into the intake manifold.  Much like a spray nozzle on the end of a garden hose turns liquid water into a spray of smaller water droplets.   If you were to aim that stream of atomized water from your garden hose, onto the hot outside metal surface of a BBQ grill, the water would vaporize, turning the atomized water stream, into a vapor.


Again, the fuel injector atomizes the fuel.  The back side of the hot intake valve vaporizes the fuel.  Reducing the atomized fuel droplets into vapor form, wherein it mixes with O2 to form a combustible mix.  Both atomization, and vaporization, need to occur to reduce the fuel to a droplet fuel size that will completely burn,  and release 100% of the energy within the fuel available.   Absent one or the other, your vehicle's performance is inefficient, wasting fuel, deficit in HP,  and creating undesirable emission gases.  This is not  theoretical or conjecture bunk.  It's a proven fact.


We do fuel injector flow testing. injector leak testing, injector spray pattern analysis, and ultrasonic cleaning of fuel injectors for almost every engine manufactured. We will pretest your injector flow rates...as they are received off your engine...ultrasonically clean your injectors...and then provide after cleaning flow test results.  We also stock replacement injectors for Jaguars and injector parts...such as o-rings, injector filters, injector hose, injector pintle caps, and injector bushings and seals.


Our home page is located at    HOMEPAGE   Check it out.  Every page on our site is available there.







PHONE AT 904-289-2020



This page last updated on Monday, March 4, 2019