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Dr. Hamman
Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5872
Experience:  30 years experience, Repairing, building, & designing, automobiles.
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1993 ISUZU Rodeo: accelerate past 60, Thoughts

Customer Question

Just picked up a 1993 ISUZU Rodeo, it will not accelerate past 60, Thoughts???
Submitted: 3 years ago.
Category: Car
Expert:  Dr. Hamman replied 3 years ago.

Dr. Hamman :

Hi, I will do my best to assist you. When you are finished please click on accept. I don't get paid unless you do. I don't know if you are a pro or a novice so we may have to fine tune the answer. I only know as much about your problem as you have told me in your post, so my answer will be based on what you have posted. Feel free to add any additional info you feel is needed.


The first thing I would check is the fuel filter. If it is dirty it will limit your top speed. It will hit sort of an invisible wall, and it wont go any faster. This can be confirmed by attaching a fuel pressure test gauge to it, and watching the fuel pressure. If the filter is dirty the fuel pressure will drop as it approaches top speed. If the filter isn’t dirty I would check the fuel pump out. If you have any more questions I am here to help. Good luck, and Thanks for using Just Answer.


I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.


Customer : I have been researching the cam sensor also, could this have an effect?
Dr. Hamman :



The cam sensor normally will not limit the speed, it is possible but rare. It will cause trouble starting, or if it starts rough and erratic operation. If the fuel filter is stopped up it will start well and rev up well in neutral. It will generally run good, but it will feel like there is a speed limiting device on the vehicle. Up on occasion a restricted fuel filter can cause the engine to run poorly in addition to the speed limiting characteristic they often exhibit. If you purchase a good repair manual it will walk you through the steps of testing various sensors like the cam sensor. A simple volt ohm meter you can get at Radio shack will perform many tests on electrical automotive parts. This saves you money by not replacing good parts. It also teaches you more about your vehicle, and vehicle repair in general. If you are going to keep this vehicle for a while, getting a good repair manual is a great move. If you have any more questions I am here to help. Good luck, and Thanks for using Just Answer.


I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.


Customer :

I was informed at a shop today the catalytic converter is stopped up, what do you think?

Dr. Hamman :


The catalytic converter could be the problem but this is one of the most misdiagnosed expensive repairs that is performed on vehicles. I would say that only about 1 in 10 vehicles that I have seen, where a bad catalytic converter was the diagnosis, actually had a bad catalytic converter. If the catalytic converter is stopped up it will run poorly in general and have a super low top speed. If the fuel filter is stopped up normally it will run good but have a limited top speed. The fuel filter only cost $20 and the catalytic converter costs hundreds, look into the fuel filter first. It is a common maintenance item that needs to be changed regularly anyway, and it may fix your problem. I have seen this over and over that is why I am cautioning you, because hundreds of dollars later if the catalytic converter isn't stopped up you will still have problems. All that being said there is a possibility that the catalytic converter is stopped up. The key here is to ask how they came to this diagnosis, and listen carefully. If they are pros there is one test, and only one professional primary test. DO NOT let them know that you know this, they cant give you a smoke screen if they don’t know what to smoke screen about. This gives you the power to not be taken advantage of, and that is a good power to have. The test is to measure the intake manifold vacuum. If they are not testing it in this manner they are guessing, and you are in jeopardy of being one of the 9 out of 10 that get their catalytic converter's replaced that didn't need to be replaced. If it is a guess it is an expensive, yet profitable guess for the shop regardless if it fixes the problem or not. If the catalytic converter is replaced, and it doesn't fix the problem the customer normally is given a bunch of garbage that it needed to be replaced anyway, and they have other problems. Use this knowledge to your advantage, and don’t let them know that you know what the test is. Many mechanics don’t know about this test so they guess. If you have any more questions I am here to help. Good luck, and Thanks for using Just Answer.


I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.


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