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 October 1996 By Mark Giammalvo
View of the troubled 5th Avenue. 

 Fig. 3 Good Fuel Pressure. 

Hooking up the fuel pressure gauge at the pressure tap on the fuel injector rail. 

 Fig 2. Checking for spark at the coils. Spark was present. 

Another investigation of spark, this time at the plug wires. Spark was good here too. 

Fig. 6 Checking for spark at an injector harness with a noid light. Hmm..the the light does not seem to pulse at regular intervals. 

Hooking up the lab scope's leads to a fuel injector while the injector remains plugged in. 

Fi8. The Fluke 97 Lab Scope is showing that the injector does not open all the time while cranking the engine. 

Fig7. The Chrysler in the intensive care unit. 

Fig 10a. Scan tool showing the car's on board computer not allowing fuel. 

Fig.10b The scan tool showing "fuel allowed." 

90 Chrysler New Yorker 5Th Avenue 
3.3 Liter 4spd/ At 
48,033 miles 
Cranks ok won't run 

Recently a customer phoned us regarding a no start condition on her Chrysler. Since the car broke down over the weekend we made arrangements to have it towed in on Monday. Due to the fact that we were two weeks booked and counting, it was decided that I would break away from my normal duties and look at the car myself. 

    On a busy Monday morning came the sound of the wreckers back up alarm. How I dread that- doot, doot, doot, doot. Anyway, I went out to great the tow truck driver. After the towing service left, I began my quest. The symptoms were still fresh in my mind since speaking to the customer, "car cranks won't run". As I turned the ignition switch to start their was no cranking sound from the starter motor-only the click, click of the starter solenoid. Needless to say, the battery was dead. Probably cranked to death by someone behind the wheel with a glimmer of hope that this car was going to start. Not this time. Normally, in this situation we would put the battery on charge overnight and look at the car again the next day, but in this case I decided to take the battery out of the car, put it on charge and then install a new battery from the stockroom so we could continue with our diagnostic. 

    Now that the loaner battery was in place we again attempted to start the car. Now we had the car cranks but won't run symptoms. Strangely enough, as the starter was held cranking the engine would momentarily seem to fire but then would just crank again. I decided to connect several spark testers in series with the plug wires to ascertain whether or not we had spark. (See fig.2) sure enough, strong spark constantly. Leaving the spark testers in place I decided that the next step would be to check fuel pressure. (see fig 3). Luckily the 3.3 has a fuel pressure  tap that is easily accessible. (Fig 4) As I hit the key - bang- 45 psi on the gauge. My next step, was to peek inside the air cleaner box just to make sure some fuzzy creature hadn't lined up 300 acorns across the air filter element. Although a restricted air supply is rare, we've been bit by that one before. Better to find out now rather than after being into the car for five hours. Air cleaner box clear! 

    After discussing the test results so far with my brother Glenn, we decided that it was time to go high tech. Connect the scan tool. (Fig 5) Logically this would seem to be the next step, after all, we can verify a supply of fuel, spark and air. But are they all being delivered? 

    Our first concern was to make sure TPS was not stuck too high. In some computer programs, if TPS is too high the computer will think someone is cranking the engine with their foot to the floor and stop fuel delivery to the injectors. We generally refer to this on GM cars as "clear flood mode". Glenn is always reminding me how nice it would be if we knew these different features of automotive computer programs on each make and model but as you already know the manufactures won't release proprietary information. Well, that's a subject for another article. Let's continue. 

    An analysis of the datastream revealed TPS was ok. We also checked to make sure charge temperature (incoming air temp) was close to coolant temp since the car was cold. They were both fine. All other datastream inputs and outputs looked good. Now, I'd be lying if I told you I didn't scratch my head a little. At this point we decided to check injector pulse with a noid light. (Fig 6) we noticed something interesting. As the car cranked their was no pulse then their would be a quick pulse and the engine would make a cough like attempt to start but wouldn't. 

    The customer called to check on our progress with the car. I told her that so far most everything we had tested had shown ok. I also told her that her car had more equipment hooked up to it than a person in ICU. (fig 7) At the end of our conversation I told her that I would call her as soon as I had some reportable news. 

    I have to digress here for a moment. Recently I was at a doctors office with my wife. My wife had mentioned to the doctor that I was often comparing medical testing on patients to diagnostic testing on cars. The doctor promptly reminded my wife that people are more complicated than cars. After we got home that evening I got around to thinking about that statement. The more I thought about it the more I realized it couldn't be further from the truth. Doctors work on only two models, male and female. On these two models they know where every organ is located. There is no change from year to year. When we work on cars we have to use large databases just to find out where everything is because their is no standardization. Whether it's a computer or a wiring harness or a solenoid, we have to look up where it is before we can even attempt to diagnose or test it. Then once we find it we need to know what specific action or output we should look for because that can change from model to model and year to year also. In addition, I have never seen a car help me my telling me where the pain or problem is. Blood and gore aside, cars are more complicated than people. Period! Back to the problem. 

    After seeing this short intermittent injector pulse we decided to check it with a lab scope. The lab scope showed that the injector opened rarely. (Fig8) 

    We decided to check for service bulletins. After reading several, we stumbled on one titled "start/stall, vehicles not equipped with Vehicle Theft Alarm (VTA)."  (Fig9) Although our symptoms were not really a start stall we thought the bulletin bared reading just the same since our car did not have VTA. The bulletin mentioned that on certain cars not equipped with VTA, the engine controller may in error, look for a VTA signal and when one is not received, prevent the engine from running. The bulletin also stated to look at theft alarm status on a scan tool and that if "fuel not allowed" is displayed while cranking, to replace the controller. (Fig 10a 10b) At first we could not find theft alarm status on our scan tool so we called our tech line. After hearing our test results they recommended replacing the controller anyway. After checking the scan tool again we located theft alarm status and verified " no fuel allowed" when cranking. We replaced the computer easily in the left front fender adjacent to the battery. After cranking with the new computer the 3.3 roared to life. Done! 

Mark Giammalvo MAT, SAE, L1 




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