It turns over fine on its own, it will start right up with a jump?

INFINITEMISSION

MEMBER
1998 GMC JIMMY
4 CYL
4WD
AUTOMATIC
176,000 MILES

My truck will turn over but will not start usually. I can get it to start by persistence occasionally but some days not at all (usually cold days). In the past I could get it to start by receiving a jump but lately that won't work. If it can get started then it runs strong and well with the exception of rough idling.

The following has been checked/tested:

1. Engine Control Modulator- Removed and tested- works fine
2. Distributor Cap- Removed and is ok
3. Firing Order- Appears to be set ok
4. Diagnostic reveals Battery, Cables and Starter ok

The following parts have been replaced:

1. Alternator
2. Battery
3 Battery Cables
4. Spark Plugs- spaced correctly.
5. Radiator
6. Fuel Filter
7. Intake Manifold- Paid to have it replaced but a friend says it looks as if it wasn't replaced but cannot confirm.

The following problems are known to exist:

1. Idles rough- was told this is a timing chain issue but the timing chain is difficult to fix?

2. Turn Signal Switch Short- The Turn Signal has a short in the wire somewhere which has been causing an intermittent clicking sound under the dashboard. The Turn Signal works fine for both the back right and left tail lights regardless of the short.

3. Alarm Wire Cut- The Alarm Wire was cut but a friend supposedly dismantled the wire so that it wouldn't drain the battery any longer.

The Diagnostic Trouble Codes have been identified:

P0304 Cylinder 4 Misfire Detected
P0507 Idle Control System RPM Higher Than Expected
P1509 IAC System High RPM

If the 'computer' was a problem then supposedly the truck wouldn't start at all.

The Fuel Pump can be heard running. There appears to be no leaks. After the Fuel Filter was installed the Gas Gauge Needle started to move up and down a bit but not violently or irradically.

Could it be a Fuel Pressure Regulator Issue or maybe a another issue?

Nevertheless I am completely frustrated as I have been getting jumps for over four months and no one can diagnose the problem correctly. I am a single mom and do not have the money to take it to the GMC dealer. How do I know if they will tack on more fees for supposed 'newly' diagnosed problems without focussing to diagnose the problem for which I submitted the truck in the first place.

Any assistance is greatly appreciated.

5 Replies

CARADIODOC

MECHANIC
33,916 POSTS

I think there are some misconceptions here. You are currently pursuing this problem the most expensive way possible. That is by throwing money away in potentially unrelated parts. There's no denying dealers are expensive, (they have to be to stay in business), but that's a whole nuther story. If you don't trust your dealer's service department, it's time to look for another shop. Every industry has their bad apples that give everyone a bad reputation.

Just to share one example, if your alternator were to fail, one shop might install a new one for you and recharge your battery while they did the service work. You could be on your way in an hour and not have any more problems. A different shop might have sold you that alternator AND a new battery. Did they rip you off. Remember, you didn't need that battery. Most people would pay the bill, leave, and complain to their friends about that ripoff shop.

The rest of the story is, ... It is very common for 1987 and newer GM vehicles to go through four to six alternators in their lifetime. They often still charge the battery, but they can cause voltage spikes that wreak havoc with the dozens of computers on the car. More and more experienced mechanics are finding out that the easiest way to prevent repeat alternator failures is to replace the battery at the same time. So, the second shop was actually looking out for your best interests, they just might not have done a good job of explaining why they did what they did. The first shop will likely get more repeat business because their repair bills are smaller, but when you have more alternator trouble in a few months, you aren't likely to blame the mechanic for cutting corners during the first repair.

That's just one example of why some shops have bad reputations. Imagine if a doctor treated someone for a heart attack, but didn't treat that person for the underlying causes.

You've listed a whole bunch of dandy clues and observations, (thank you), but they suggest a few different circuits or systems could have problems. If it turns over nice and strong, it should start without a jump-start. The fact that it was starting better with a jump-start suggests a battery or alternator problem.

The timing chain you mentioned could be involved in the rough running, but it isn't the total cause of the no-start. I would like this problem to be related to the alternator or battery because I am very familiar with that circuit, but since you already replaced them, we'll have to look somewhere else. Can you take a voltage reading between the two battery terminals during cranking when the engine doesn't start? We have to start somewhere, and that is as good a place as any.

Caradiodoc