As indicated and out of sheer desperation I’m reaching out to this community. I went on a trip for work for slightly over a month in November. After returning, I drove my ‘92 Buick Roadmaster wagon (41 miles) to work without event. When I drove home, the car flashed a check engine light (code 45 rich mixture) and subsequently was a handful to maintain running. Hard oscillating at idle with subsequent dying.. I’ve since replaced the O2 sensor, TPS sensor, temperature control sensor, idle control sensor, replaced the ecm, map with known good pieces, checked the fuel pressure at steady 12 psi, checked the vacuum at a steady 18 inches of mercury, checked the ground reference and all engine grounds to the distributor, looked at the fuel injection nozzles for proper operation, changed the fuel regulator in the tbi. Checked and verified the ground reference circuit for the Hei distributor and all associated circuits in conjunction with the ECM. but yet the car runs rich and trips a code 45.. All vacuum hoses are in tact/soft. The car idles perfectly until a given time….then falls apart. Please advise. I’m all ears and grateful for professional assistance.. I have read my factory manual, but am running out of options…

 

Make sure the egr valve is not stuck open and that there is no vacuum going to it at idle.

 

I put my brake vacuum tool onto the egr this morning and verified that it was functioning properly. Then I started the car to verify that it remained closed while still cold. I had replaced the egr about 1.5 years ago. Thank you for your input.😊

 

I’ve also ran the car and sprayed starter fluid liberally at tbi base and intake mating surfaces both cold and during surging with no appreciable changes in RPM.

 

Put a scanner on it and read the temp. Forget the factory guage, need to see what the CTS is inputting to ECM.

 

The one thing you have not really done is to check and see if it is actually running rich ? Do you know anybody with a wideband O2 setup that you might be able to borrow and do some checks ?

Also, if the O2 sensor is indicating a rich mixture don't rule out a bad sensor even though it is new. What brand O2 did you use ?

 

Unfortunately I don’t have access to any machines to measure the exhaust mixture.. Earlier today I isolated the evap system with same results. Then I checked the temp sensor circuit for shorts, with no defects. The temperature sensor was a Standard brand, and I’ve read that they are hit or miss as far as quality. I ordered a Delphi temp sensor to see if the results are better. Thanks for your input!

 

What brand O2 sensor did you use ?

Do you have a scanner that can actually read the O2 sensor and other sensors ? If you dont you are just throwing money at it.

 

I only have a generic OBD1 scan device.. You are correct, it could be perceived that I am throwing parts at my car. But here is the alternative view…. The car is 33 years old. Parts are accessible and inexpensive (even if buying factory parts). My labor is an inconvenience, not an expense. If I pay another mechanic to perform the same work I’m doing, the labor costs will exceed the price of shotgunning parts very quickly. (This is a primary reason why cars are retired in the general public). Not to mention the fact that I can retain parts for future diagnosis. The additional benefit is my personal learning of how the vehicle operates. I consider the price of the parts and diagnostic gauges to be a small price to pay for the experience and ability to properly diagnose problems in the future. Thank you very much for sharing your experience, I sincerely appreciate it!

 

You'll need to read the data to determine what's going on.

 

Do you have a suggestion for a reasonable source to collect the data to make an educated assessment? I’m not being smart, I’m absolutely VERY interested in your suggestion. I intend to drive the wheels off of this vehicle and appreciate any feedback to help me keep my vehicle healthy. Please advise..

 

A used early scan tool can be had for cheap. Something along the lines of a snap on mt2500 or early Mac mentor (OTC) with a GM1 Adapter.

 

Thank you 66 Jetstar, I will certainly look into this.👍

 

Funk,
I just want to say that for the amount of money you have wasted to this point you could have easily paid a good repair shop an hours labor to hook up a scan tool and tell you what was probably wrong. Then either you could pay them to fix it or fix it yourself but throwing parts at it without having a clue what is causing the problem is not very productive.

Just a thought

 

Shotgunning parts not a good idea. Save your old parts. Another suggestion if that one of the fuel injectors might be overactive. Not sure how to test those. You need an old OBD 1 scanner, I believe, to read live data. Follow the factory manual trouble shooting guide to diagnose.

 

Thank you for all of the suggestions and expertise shared with my ongoing problem. After an extensive troubleshooting regime which included individual wiring circuit examination, component exchanges and a lot of nighttime thought assessments, I’m confident that I’ve finally resolved this problem. The problem was either the engine to body ground strap (white corrosion) or an obstructed catalytic converter. (Or perhaps a combination of the two). The car has 214,XXX miles. After thoroughly cleaning the ground circuit and removing the 33 year old converter, my car is finally able to maintain an even idle while sitting in traffic. As a side note, I don’t feel as though I’ve wasted money on parts…. I’ve simply renewed 33 year old electronics that were already destined for failure at any given time. I have since acquired access to an old school diagnostic with live feed capabilities.. I’m not so sure that it would have solved my problems, because it is not as straightforward as modern OBII diagnostics. I am looking forward to experimenting with its capabilities and continuing to learn how to use it and hone my knowledge. Thank you all for your help.

 

Glad you got it fixed. To bust your ***** usually the first or second step in all the diagnostic flow charts is to check/inspect all the grounds!!!

 

I’ll humbly and happily accept your ball-busting for the sake of raw experience. It is irreplaceable!😂

 

I agree completely on OBD1 diagnostics, they sucked. A lot of time they wouldn't even leave codes until the vehicles would hardly run. You would test, follow flow charts and hope it fixed the issue. Glad you found it.

 

Reluctantly, as a follow up I drove the car for two weeks/41 miles each way without any problems. I was sitting in traffic on the way home every day without any surging problems. At the beginning of the third week, it died once in traffic. The following morning it surged leaving my neighborhood, and regressed to hard surging/dying in traffic on the return home…. I’ve since purchased an OTC enhanced 4000 OBD1 diagnostic scanner and am able to monitor what some components are doing. A co-worker loaned me a different tbi for troubleshooting purposes, which the problem was duplicated validating that it is not the issue. The car runs terrific until it goes into closed loop. 13psi fuel,19 inches of steady vacuum, cat delete, clean injection spray, grounds/circuits verified, ecm swapped x3, O2 circuit validated, evap system validated, ignition system validated, timing/chain slop validated, voltage good. I’ve driven and loved these TBI’s for 21+ years , and have always raved about their reliability. Now all of the sudden my friends are telling me to LS it…. I don’t want to, if I can fix it, it will be just fine… Frustrating

 

Try unhooking the EGR for a while (plug the vacuum source). The 350 TBI in my 95 Suburban was doing that crap. A friend suggested it was because of the free flowing exhaust, and had a similar problem. I unhooked the vacuum line and put a cap on the controller port. Problem solved, no more surge.

 

Thanks, I isolated the egr and put my vacuum gauge in lieu of the EGR. Ran to closed loop and duplicated the problem. Vacuum never indicated as the throttle (tps) was not actuated. Just for funnsies, I swapped out the map sensor with typical results. The problem is clearly an issue of when the ecm goes into closed loop. Diagnostic continues to show 1.7 volts rich, idle hard ossilates until dying, or tripping a service engine light and reverting to open loop.

 

After six months of exhaustive troubleshooting, I have finally located the source of my issue. The wiring harness to the front of the engine wraps around the front of the oil pan. The alternator excitation lead insulation had a worn/deteriorated portion which was shorting to the power steering circuit and the O2 circuit providing excessive voltage to the ECM to indicate a hard enriched exhaust. I removed the harness, cleaned, repaired and secured with fresh split loom. Ran the car last night with normal O2 readings switching rich/lean as advertised. Very happy to put this problem to bed..

 

Finally Heath, no quitting!

 

Right!! Now on to more exciting things like TKX conversions!!