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Brian Barr
Brian Barr,
Category: Chevy
Satisfied Customers: 22
Experience:  head tech at Jrs Automotive Sales and Service
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I have a 1991 Chevy Blazer TBI 4.3 that runs very rough and

Customer Question

Hello, I have a 1991 Chevy Blazer TBI 4.3 that runs very rough and does not idle properly
JA: How many miles are on the car? Have you checked the spark plugs?
Customer: New spark plugs, new distributor, new plug leads, new map, new idle air control valve and new injectors
JA: What is the model of your '91 Chevy?
Customer: 1991 S10
Blazer
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: yes
JA: Anything else you think the mechanic should know?
Customer: fuel pressure is 1 Bar
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Chevy
Expert:  rpmdiag replied 1 year ago.

Hi, I’m Ron and I can help you.
I have been in the auto repair business with my own shops since 1975 and also teach automotive repair. I am confident we can resolve your problem together. Please understand that I don't know your skill level. In most cases when you have a problem with the way the vehicle performs, specialized tooling is required to acquire computer data/information or engine testing results. We didn’t build these complicated vehicles; we just diagnose and fix them. Also understand that I can't see, smell, hear, or touch the vehicle either, so it may take a few replies to get to satisfactory results. I am also going to direct you with the fastest, easiest and most common things to check first. Please be patient and permit me to do what I do best.
I also try to give all of the information you may need, expecting a “positive rating” in return. I will also continue assisting you after you have rated me, if necessary. If there is any reason I cannot get a positive rating, please let me know why “in advance”, so I can go another direction for you. I am sorry you’re having this problem; I’ll help you through it.

You should do a compression test and also look for vacuum leaks and scan the computer for codes.

Thanks, Ron

Customer: replied 1 year ago.
I have no codes or vacuum leaks, already checked, please check the supplied information regarding all that i have tested. The vehicle runs perfect if i turn on the Backup spark and fuel on
Expert:  rpmdiag replied 1 year ago.

I did read everything, it doesn't say anything about what I asked you. This can be a computer problem due to the new information. Do some bidirectional commands with you scan tool to verify.

Thanks again, and please don't forget to rate me and keep this link in case you need me again later on.

Ron

Customer: replied 1 year ago.
I dont know what bidirectional commands are?
As i said i have no error codes whatsoever, if i start it and run it, the car hunts and then dies. If i play with the accelerator i can keep it running but if i keep my foot at a certain position then it just backfires through the throttle body. It looks almost as though the injectors are switching off. I replaced the fuel pump because the pressure seemed low, it is now on 1 bar and before the fuel pump replacement it was around 0.8 Bar
Expert:  rpmdiag replied 1 year ago.

Pressure is good. I would check compression for valve timing being off.

It is important to run the other tests recommended too. Guessing is very tough:)

Ron

Customer: replied 1 year ago.
What other tests? Other than the compression test.
Would a it still run well if the valve timing is out and all i do is activate the backup spark and fuel?
Wayne
Expert:  rpmdiag replied 1 year ago.

MODE 6 tests for computer malfunction.

It could run good if the computer is adding a lot of timing to compensate for a malfunction. These tests are important.

Thanks again, and please remember to rate me for my time.

Ron

Customer: replied 1 year ago.
What is MODE 6? I have a Snap On Scanner
Expert:  rpmdiag replied 1 year ago.

It's one of the 9 functions your scanner is capable of. It tells you data that the computer sees and calculates.

Thanks again,

Ron

Customer: replied 1 year ago.
With all due respect your answers are not of much help to me.
What should i be looking for that would stand out? The computer is showing no malfunctions. One day it was driving fine but idling high and the next it just doesnt want to idle anymore. I seem to be leaning towards a computer fault but i live in South Africa so its not that easy to get the stuff that i need to fix it with all the parts having to come from USA.
What should i do to perform the test that would see if there is a computer fault? I can read the data and it all appears to be normal apart from the O2 Sensor staying on lean and not much activity on it. The MAP sensor is working as it should with the voltage and the hz working in connection with one another, the temperature switch is working fine as is the Idle air control valve. What is it that i am missing? The knock sensor did show 17 on it, could that be faulty? Please help with your guidance
Expert:  rpmdiag replied 1 year ago.

here is a link about MODE 6. I teach a 5 day course on this, 8 hours a day. It isn't anything that can be done in ten minutes because it's extremely involved.

http://www.autoserviceprofessional.com/article/94970/obd-ii-mode-6-making-it-part-of-your-diagnostic-arsenal

Thanks again, Ron

Customer: replied 1 year ago.
Thank you Ron, i appreciate all your assistance in trying to help me out. I cant seem to find a MODE 6 on my Snap On Solus Ultra. Would you know where i can find this and if its available for my vehicle as i read that it was introduced in early 2000 and my Blazer is a 1991 model.
Wayne
Expert:  rpmdiag replied 1 year ago.
It does it, go to global OBD2. It should be in there if I remember right.
Thanks again,
Ron
Customer: replied 1 year ago.
Hi Ron,
Ive gone into the OBD2 and tried the EOBD as this is not an OBD2 vehicle and there is no communication. I also tried OBD2 and there is also no communication with the vehicle. Tell me, will a bad O2 Sensor cause all the problems that im experiencing? It seems to stay in the range of 447mv to 450mv under acceleration and deceleration.
Thanks
Wayne
Expert:  rpmdiag replied 1 year ago.

I'm sorry, but I am not familiar with all the scan tools that are out there. Your tool does have a section in it for information like this. I hope you don't let this reflect my rating, we just can't know every tool that everyone has.

Thanks, Ron

Customer: replied 1 year ago.
Hi Ron,
Are you just referring to the Live data stream? If so then im already in that and this is where im getting my information from that i have been supplying you. What about the answer to my question on the O2 sensor?
Wayne
Expert:  Brian Barr replied 1 year ago.
Hi there I will try and assist you with your issue.
Expert:  Brian Barr replied 1 year ago.

If the oxygen sensor is staying stuck in one range it can richen or lean the fuel ratio causing similar issues you are having.

Customer: replied 1 year ago.
Ok, that's what I wasn't sure about, On Monday morning I will change out the Oxygen sensor and report back
Expert:  Brian Barr replied 1 year ago.

Ok sounds good!

Customer: replied 1 year ago.
Hello Brian,
So i have checked and the Oxygen sensor is there but there is no wire to the ecu on to it. Do you know where this would sit on my van?
Thanks
Wayne
Expert:  Brian Barr replied 1 year ago.

Hi Wayne

Are you meaning what is the ECU pin for the oxygen sensor?

Thank you

Customer: replied 1 year ago.
please, i have a factory manual for my 1996 model but that has the Vortec Injection and is completely different. Perhaps you will have a wiring schematic for the O2 sensor?
Customer: replied 1 year ago.
I found the plug tucked away and connected it up, its now got some movement on it but i still have the same original problem, It wont idle without hunting and then dying. You can rev the vehicle up but you cannot keep your foot on a certain rev, it feels like fuel starvation but i have fitted a new fuel pump and have got great fuel pressure now. Still no error codes
Customer: replied 1 year ago.
i sorted my truck out, thanks to youtube. There is a guy out there that made a video with exactly the same problems i have been having and it turns out that the new injectors that i fitted are at fault. Cleaned and fitted the old injectors and fitted the new O rings and filters and it runs like a dream again.
Expert:  Brian Barr replied 1 year ago.

Awesome glad to hear