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'88 Deville Gold Edition cant accelerate past 45mph

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I have had this 1988 Cadillac DeVille Gold Edition for over a year now. It is the 4.5L V8 4D. After about a month of having it, it started having a problem where if I attempt to accelerate passed 45mph it jerks the car so hard it feels like the engine just physically stopped for a split second but then continues. Any time I try to speed up after that it does it, but only 45mph. It does not matter whether it is downhill, uphill, or level. I found a broken vaccum line a while ago and fixed it. I've tried replacing plugs and wires, fuel pump, fuel pump wiring, cleaning injectors, cleaning atomizers(?), tried another ECU and body module, checked fuel pressure with gauge while driving around town, fuel line cleaners. I have even tried different oil and transmission fluid. The error codes do not seem to come back with anything useful according to a chart I printed out. I finally got ahold of the person who sold it to me and he told me he had trouble with the Dimmer switch and believed it was worn and shorting, so I replaced that and it did not help. Also, on some days if I turn the dimmer as bright as it goes the engine either nearly dies, or just shuts off, but no other object in the car drawing power causes it, only the dimmer, not even headlights. I have turned on cruise control, brights, hazards, wipers, dome lights, radio, and moved the seat all at once and the engine did not flinch. I do know the front main seal is seeping a bit. Now here is the weird thing, every time I have replaced a part, including the dimmer switch, the car seems completely fixed for roughly 1-2 weeks, then continues with exactly the same issues. Car only has about 127k miles.

I am open to ideas, I know some basic mechanics, but nothing elaborate but do live with mechanically inclined people who cannot figure it out either.

I am out a lot so feel free to email me at jssloanva90 @ yahoo .com if you believe you know.

Thank you,

Desperate Caddy owner on his last leg.

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The fuel pressure on a TBI engine should be 9-13 psi. Have you verified that while the car is acting up?

Simultaneously press and hold the OFF and WARMER buttons on the climate control panel and there will be a series of codes displayed on either the fuel data panel or the climate control panel. When you see .7.0, the system is done displaying the codes.

There is a vacuum line that connects to the underside of the throttle body on that engine and connects to the MAP sensor. Sometimes, the rubber connector tubing gets rotted/brittle and causes a severe vacuum leak. Something to check.

The other thing could be a plugged/restricted catalytic converter.

Check the codes first and post them back. If there are any codes, they may provide a clue to what's going on.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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24 year old car. Really could be anything.

The dimmer switch issue is interesting.

As nice as the self-diagnostics are....I think it's worthy of plugging in a Tech 1 or Tech 2.

Maybe a bad ground somewhere.

Maybe bad battery cables.

A plugged cat crossed my mind too.

Maybe 'green' connections on the pick up coil or ignition module in the distributor.

There is a old TSB about a goofy engine ground near the starter on Cadillacs. It's on the front of the engine block...kinda right next to the starter. It may look ok but needs to be taken apart and cleaned.

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Actually went and looked up the TSB. The more I thought about it...you need to check that ground. I've seen this ground cause multiple goofy issues....some issues not even listed in the TSB.



Some 1988-1990 DeVilles, Fleetwoods, Eldoraods or Sevilles may experience one or more of the following driveability symptons:

Engine Surge/Miss at idle with high electrical load or A/C load

Erratic secondary scope patterns

Intermittent stalls

Intermittent loss of power

Black smoke/rotten egg odour from tail pipe



Intermittent no start

Poor fuel economy

These conditions may be caused by a poor engine ground. This results in erratic EST operation as commanded by the ECM.

To service this condition it is important to remove and clean the ground stud by the starter. Install a star washer, p/n #11501869, on both sides of the stud to engine block. For location on DeVilles and Fleetwoods refer to Figure 1: for Eldorados and Sevilles refer to Figure 2.

Parts are currently available from CANSPO.


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I will check on all of those things and certainly check that ground. I will post codes and findings next chance I get. I apologize for the late reply, I am traveling and am not near the car this week. I highly appreciate the assistance in this matter. I have not been able to use the car in a long time. The car looks amazing but as Logan said, it is a 24 year old car, bound to have something happen. Thank you.

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