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Ms. Wrench
Ms. Wrench, ASE Certified Technician
Category: Car
Satisfied Customers: 554
Experience:  ASE Certified Technician-10 yrs., Service Writer-Foreign, Domestic & Fleet, Alternative Fuel Expert
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90 Olds 98 Regency: sensor coil pack

Customer Question

I have a 90 Olds 98 Regency and has been a "champ" up until lately. It starts and seems to "rev" nice until I place it in gear drive/reverse. Just sitting in gear at a light or when I accelerate it seems to miss,like on all cylinders,then recovers ,then misses,then recovers.....once I am up to speed it is less prevelent......but "it" is happening just not as noticable, very pattern like ,no codes have manifested themselves I have replaced crankshaft sensor,cam sensor coil pack, ignition module...checked the fuel pressure regulator, seems O.K. 40 psi but spikes/drops as engine misses.......any help would be appreciated
Submitted: 8 years ago.
Category: Car
Expert:  Ms. Wrench replied 8 years ago.



This is Ms Wrench and I can help you with your 1990 Oldsmobile Regency 3.8L.


From what you are describing it sounds to me like the problem is with your fuel pump. If you are getting spikes and drops in fuel pressure that coincide with the engine missing then the problem is most likely erratic operation of your fuel pump.


One thing you can check is the fuel pressure regulator vacuum line to see if there is any fuel in it. If so the regulator should be replaced, but the problem is likely to be a bad fuel pump. Especially since you are having the running problems you are with no codes setting.


I don't know if you would have the equipment, or maybe your mechanic does, but a low amp probe of the fuel pump circuit on a graphing meter would tell you immediately the condition of the fuel pump. If you want more info on this let me know.


With all the other repairs you have done I am advising you that you probably need a fuel pump at this point.


Let me know what you find out,


Thanks for using JA


Ms Wrench

Ms. Wrench and 8 other Car Specialists are ready to help you
Customer: replied 8 years ago.
O.K. heres what I found, did a little checking and fuel pump was stopping momentarily as car was running......but recovering almost immediately................... hot wired fuel pump circuit ,put vacuum source (12 hg) on regulator on the fuel rail and ran the pump (car off) and it (fuel pump) ran forever. Did not skip a beat...................then I started car, keeping vacuum source and fuel pump hot wired.........and car ran great for a little bit....only to fool me........seemed to stutter, very rhythmically especially when in gear with a little gas (under load).....same symptoms when all this crap manifested itself in the first place...........checked (oil pressure) sending unit and according to wiring diagram as it looks to be only source of power to fuel pump when car is running,however cannot be totally sure as "program" in ECM might keep relay on or turn off relay when oil pressure drops, car is in accident etc. So I figured what else would manifest this .....I know disconnecting temp sensor shut it (the engine) down and crankshaft position sensor shuts it (the engine down) so with ignition switch on I noticed I could get fuel pump to come on momentarily (priming circuit, 2 seconds) when I plugged "in" and "out" crankshaft position something is in the "program" safety feature I pulled secondary wiring harness (ignition module,crank pos. sensor, cam pos. sensor) and examined..........two of the four of the intrinsic tangs in the female connector which make intimate contact with the pins in the crank sensor were fatigued and had fallen off..... so replaced and spliced in new connector.....also "tuned" the others up on all the other connectors in the harness by sliding (de-pinning) them out and rebending the tabs ......needed my magnifying head lens as these things are tiny.................well it's far so good......but although the fuel pump was not the failure, your advice at least forced the issue to rule it out as the primary cause , what would have helped (not from you of course) was the actual program in the ECM as I eventually got the "drift" of the logic but it would have been nice to see what caused the rhythmic surges , it seemed to happen also after the engine warmed up to operating temperatures....also the "time" and scan times for faults to "register" in the fault code ,anyway thanks again, this was a tough one to say the least......lot of midnight oil burned looking at wiring diagrams..... bench simulating sensors and output responses..........thank you ,best regards XXXXX XXXXX