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90redsc
05-08-2017, 07:18 PM
Car starts fine: when you accelerate gradually it's fine. But when you hit the throttle to accelerate and it kicks down it bucks violently until you take your foot off . It did it once or twice in the beginning. Now it's all the time. Replaced fuel pressure regulator. No affect. Also, no codes or check engine light on. Ideas????
1990 X7 auto

KMT
05-08-2017, 08:03 PM
Done anything w/plugs and wires lately?

Done any engine cleaning recently?

See any evidence of rodent nesting?

How old is the fuel?

Checked the harmonic balancer?

90redsc
05-08-2017, 08:21 PM
Nothing with plugs or wires
No animals
No eng clean
Dampner is ok

90redsc
05-08-2017, 08:22 PM
Fuel is new

KMT
05-08-2017, 08:31 PM
Does the tach jump around?

How many miles on plugs/wires?

Any mods?

Manual or auto trans?

90redsc
05-08-2017, 08:34 PM
Tach jumps until you take foot off throttle
6k on plugs and wires

90redsc
05-08-2017, 08:35 PM
No modifications

90redsc
05-08-2017, 08:36 PM
Auto trans

KMT
05-08-2017, 09:04 PM
Most times w/these cars, plug wires are the issue when you see heavy miss/bucking.

I'd go over them carefully to be sure they're still fully seated - as hard as that can be to do.

Might want to search here on tach jumping, just to be familiar w/that issue and it's causes.

90redsc
05-08-2017, 09:08 PM
I'll check k them. Thanks

TbirdSCFan
05-08-2017, 09:44 PM
I'd vote for plug wires.. not seated fully. :eek:

But something else you can do is to disconnect the cam sensor. See if that clears it up. :cool: Takes multiple tries to start the car, but once its running it will run fine. If the problem goes away, replace the cam sensor.

90redsc
05-09-2017, 05:28 AM
I'll try that also

decipha
05-12-2017, 07:51 AM
sounds like my original 90 sc I got from jersey back in 08, the problem on mine was that one of the plug wires was melted by the exhaust and the coil was on its way

replaced both and it ran perfect, up until the crank split

90redsc
05-13-2017, 07:57 AM
Any particular brand of wires you recommend?

90 red sc
06-04-2017, 01:37 PM
Thanks millions guys. New plugs and wires did the trick. Runs great!

KMT
06-04-2017, 01:41 PM
Thanks for the follow up ;)

90 red sc
06-19-2017, 01:18 PM
As I indicated before I changed the plugs, wires and cam shaft sensor. The bucking has stopped, but now after a short period of time the check engine light goes on. When I pull in the drive way shut it off and try the restart it acts like it has a dead battery. Let it sit for and it will restart. And no check engine light. I also replaced the DIS since the tach seems to act up also. Previously the batter and relay had been replace. Any thoughts on this for the next step would be appreciated.
There is no change in performance when the car is running the check engine light comes on.

90 red sc
06-19-2017, 01:34 PM
As I indicated before I changed the plugs, wires and cam shaft sensor. The bucking has stopped, but now after a short period of time the check engine light goes on. When I pull in the drive way shut it off and try the restart it acts like it has a dead battery. Let it sit for and it will restart. And no check engine light. I also replaced the DIS since the tach seems to act up also. Previously the batter, starter and relay had been replace. Any thoughts on this for the next step would be appreciated.

KMT
06-19-2017, 02:14 PM
>When I pull in the drive way shut it off and try the restart it acts like it has a dead battery.

If that means nothing happens when you turn the key/won't turn over at all - at that point, what is the voltage at the battery?

If you turn on the headlights, do they work good? If so, what happens to them if you try to start the car? Do they dim?

After replacing components, did you disconnect the battery so the EEC can learn new inputs?


>after a short period of time the check engine light goes on

Did you check the codes?

90 red sc
06-19-2017, 02:27 PM
Did not check codes at this point. I did not disconnect the battery.
Should I do that first and see if that resets?

90 red sc
06-19-2017, 02:28 PM
Here is my plan tonight.
Disconnect battery and allow to reset. Then see how it starts and take a voltage reading.

KMT
06-19-2017, 02:45 PM
Might as well check volts after resting the battery too.

90 red sc
06-19-2017, 02:56 PM
will do thanks.
Will let you know how it turns out.

sam jones
06-19-2017, 03:18 PM
As I indicated before I changed the plugs, wires and cam shaft sensor. The bucking has stopped, but now after a short period of time the check engine light goes on. When I pull in the drive way shut it off and try the restart it acts like it has a dead battery. Let it sit for and it will restart. And no check engine light. I also replaced the DIS since the tach seems to act up also. Previously the batter, starter and relay had been replace. Any thoughts on this for the next step would be appreciated.

Good morning

Need better description of "dead battery". Is this a no crank or crank with no start condition?

I would do the following:

- Pull the EEC codes; Key On Engine Off and Key On Engine On. Address/correct issues as suggested by KMT.

- Remove steering column covers and check for separation of the ignition switch.

- Key On Engine On. Do you hear the fuel pump prime the fuel injectors?

- Key On Engine On. Crank and attempt to start. Is the instrument cluster Up shift arrow indicator ON? This would be a strong indication of a crank sensor/harmonic balancer issue.

- Key Off Engine Off.

- Jack and Support front of car. Inspect the following:

- Evidence of coolant leakage on the crank sensor. Remove the harmonic balancer covers (if installed). Correct leakage if found. Highly recommend replacing the crank sensor.

- The harmonic balancer/pulley for broken/missing bolts. Broken/missing bolts require harmonic balancer replacement. Would highly recommend to replace the crank sensor at the same time.


Good Luck.

TbirdSCFan
06-19-2017, 05:25 PM
The bucking has stopped, but now after a short period of time the check engine light goes on. When I pull in the drive way shut it off and try the restart it acts like it has a dead battery. Let it sit for and it will restart. When it bogs like that when you're cranking it, let off right away and retry. For reasons I can't explain, the ignition timing has gone out of wack. Its almost as if the Cam sensor has come unplugged... even though it hasn't. When you retry, the EEC makes another guess at timing and usually the car starts right up again. Unfortunately, I don't know the cause of this with an otherwise, healthy set of ignition components... that is DIS, EEC, cam sensor, crank sensor. :confused:

Oh, and if the light comes on, and subsequently goes out, there should still be a stored code for you.

james5275
06-19-2017, 10:23 PM
My 90 aod has done the exact same thing for years (without the cel). Only with a warm engine, if you shut off quick then try to restart, the ignition occurs early and kicks back against the starter. Just release the starter then try again. A few other people have experienced this too, never found a solution.


JJ


When it bogs like that when you're cranking it, let off right away and retry. For reasons I can't explain, the ignition timing has gone out of wack. Its almost as if the Cam sensor has come unplugged... even though it hasn't. When you retry, the EEC makes another guess at timing and usually the car starts right up again. Unfortunately, I don't know the cause of this with an otherwise, healthy set of ignition components... that is DIS, EEC, cam sensor, crank sensor. :confused:

Oh, and if the light comes on, and subsequently goes out, there should still be a stored code for you.

KMT
06-19-2017, 10:48 PM
> A few other people have experienced this too, never found a solution.

W/those symptoms, seems the solution that many have found is always the cam sensor.

The OP, however notes that the bucking issue is solved and has moved to a new problem - having a no start issue/weak battery, I believe.

KMT
06-19-2017, 10:53 PM
>For reasons I can't explain, the ignition timing has gone out of wack.

In that example, the issue is no CID from the cam sensor, forcing the EEC to guess, where one out of three wins. Wrong guesses equal incorrect timing.

The OP has dealt w/the bucking issue and now has a basic no start, so even if the solved issue remained, they can't "let off right away and retry". Perhaps the battery is low for some reason and otherwise needs to rest between tries.

TbirdSCFan
06-20-2017, 12:13 AM
The OP has dealt w/the bucking issue and now has a basic no start, so even if the solved issue remained, they can't "let off right away and retry". Perhaps the battery is low for some reason and otherwise needs to rest between tries.

If at the beginning of the day the car started with a healthy start, that is a fully charged battery, and some time later on in the very same day he has a restart with a warm engine that he describes: "When I pull in the drive way shut it off and try the restart it acts like it has a dead battery. Let it sit for and it will restart. " :confused:

Sorry, but I've never had a battery get tired, rest, and rejuvinate itself over 1/2 hour.

That means there's likely nothing wrong with the battery, nor charging circuit. It doesn't hurt to check the charging circuit. Thats the prudent thing to do. But when that checks out, (which it will in my experience), you're left scratching your head and chasing a ghost. Thats because, and its been verified by at least 3 owners on this same thread, there is a condition where preignition occurs causing the engine to start hard.. as IF THE BATTERY was low. You verify that condition by taking another prudent action and letting off and retrying the start. It costs you absolutely nothing in terms of time.

90 red sc
06-20-2017, 02:18 PM
Reconnected battery this morning car started once around the block check engine light went on. Pulled into driveway shut down. Restarted no light. Pulled codes. KOEO 11. KOER. 41. 91 77 74. No check engine light came on.

You may recall the following items have been replaced
Plugs and wires DIS Cam sensor battery is less than 2 months old. Also starter and relay have been replaced. Tach still not functioning as it use to.

KMT
06-20-2017, 02:29 PM
Pulled codes. KOEO 11. KOER. 41. 91 77 74. No check engine light came on.

You may recall the following items have been replaced
Plugs and wires DIS Cam sensor battery is less than 2 months old. Also starter and relay have been replaced. Tach still not functioning as it use to.

The KOEO code says no issues. KOER codes make me wonder if the engine was warmed up fully before testing.

About the tach - remind me, was that an original issue when the bucking happened, or did it start right after new DIS and cam sensor, or? Did you use the paste on the bottom of the DIS when you installed it?

90redsc
06-20-2017, 03:45 PM
I notice the tech issue when this started. Yes I put dielectric on the DIS. Could it be crankshaft sensor ?

KMT
06-20-2017, 04:40 PM
When starting, is the upshift light on in the dash cluster?

Without more evidence, it could be a number of things. Interesting this happened after new items.

What kind of shape is the electrical harness in that connects to the DIS and cam sensor? Any damage or oil soaking?

Can you check the crank pulley to see if it wobbles or feels loose?

90redsc
06-21-2017, 06:00 AM
No upshot light at start. Wiring harness not in best of shape. No oil soaking or issue with dampner. Any place to get replacement wiring harness or do you have to rebuild from scratch?

sam jones
06-21-2017, 09:19 AM
No upshot light at start. Wiring harness not in best of shape. No oil soaking or issue with dampner. Any place to get replacement wiring harness or do you have to rebuild from scratch?

Good morning


Check the routing of DIS harness connectors cam/crank sensor and the supercharger belt. An improperly routed harness can "rub" and eventually chafe through the wires. As for a replacement harness (other than the salvage yard) try the wanted/sell section of SCCOA, SuperCoupe Performance and or Spinning Wheels restoration section.


Good Luck.

90 red sc
06-21-2017, 09:30 AM
I'll check the wiring as you indicated and see what I find. If wires need replacement, do you know what gauge it would be?

KMT
06-21-2017, 09:55 AM
The harness includes shielded wiring and has to be correct, just like factory. I'd do my best to find a replacement instead of trying to make one up. Check with the vendors sources Sam listed.

90 red sc
06-21-2017, 12:50 PM
ok thanks for the help