89 MTX bucks and resists acceleration until secondaries

Dougies for 89MTX

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Hello y’all, I have an 89MTX. As the title suggest it resists accelerating, as in, it will no smoothly rev or accelerate. If you mash the pedal it will back fire for a bit until the revs bounce up and down; then the secondaries kick on and it will rev from 5k to 7k. I have had it a few times where it ran smoothly however a majority of the time this is how it behaves. When it is acting up, you stop moving and idle, it will idle between 100 and 200rpm. This low idle sometimes causes the car to stall when letting out on the clutch in order to start moving. So far I have replaced, spark plugs and wires, valve cover gaskets, cam position sensor, tps. I have unplugged the battery for Atleast 30 seconds and have attempted to clean maf and IAC. The maf made no difference when unplugged. I have also cleaned and retightened the grounds that I could find, as well as, replaced any damaged vacuum lines. Just yesterday I applied dielectric grease to the primary sensor connectors and added zip ties to the loose ones. I am considering a DIS module due to my symptoms which are: erratic Tach, back fires, rough acceleration, poor idle when other symptoms occur, as well as, my codes which Atleast 2 were ignition circuit failures. Any input greatly appreciated
 

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luigisho

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IF you can get the codes accurately that would help. I would verify firing order, check DIS, consider IAB/IAC as cleaning can help but if it is far gone it won't. Same with MAF. Cleaning sometimes helps and sometimes not. However if it was strictly MAF unplugging should have provided some sort of difference in running. Alot of things on the table still.
 

rubydist

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We need the actual codes to help you.
 

rubydist

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18 = tach signal is erratic
45 = coil primary failure
48 = coil primary failure
67 = neutral circuit failure

Smaller number codes are more important, so fix those first. The tach signal being erratic is usually a bad cam sensor. With this code, the engine will run very poorly with varying symptoms in my experience. I would unplug the cam sensor to test it. With the cam sensor unplugged, the pcm has to guess which cylinder is number 1, so it may take several cranking attempts to get the engine to start. Once it starts, it should run normally although obviously with no tach reading. If that is the case, replace the cam sensor.

In these vehicles, I have never had a coil failure code actually be the coil, it was always the DIS. So, if the cam sensor does not fix your problem, the next thing I would do would be to replace the DIS.

I have also had issues with opens in the wiring harness, so either of those codes could be the result of a wiring harness issue. Those are much more difficult to chase down, in my experience.
 

Dougies for 89MTX

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18 = tach signal is erratic
45 = coil primary failure
48 = coil primary failure
67 = neutral circuit failure

Smaller number codes are more important, so fix those first. The tach signal being erratic is usually a bad cam sensor. With this code, the engine will run very poorly with varying symptoms in my experience. I would unplug the cam sensor to test it. With the cam sensor unplugged, the pcm has to guess which cylinder is number 1, so it may take several cranking attempts to get the engine to start. Once it starts, it should run normally although obviously with no tach reading. If that is the case, replace the cam sensor.

In these vehicles, I have never had a coil failure code actually be the coil, it was always the DIS. So, if the cam sensor does not fix your problem, the next thing I would do would be to replace the DIS.

I have also had issues with opens in the wiring harness, so either of those codes could be the result of a wiring harness issue. Those are much more difficult to chase down, in my experience.
Ok great, the dis arrived to O-Reilly’s, so in the morning I’ll slap it on and update y’all.
 

luigisho

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DIS tips. Make sure to get the thermal paste on the back to keep heat away from the electronics inside. If you have excessive engine movement under the hood (mounts) it can also flex the wiring that plugs into the sides of the DIS and can cause issues in short order. It can crack the connection tabs and into the module. The car is old but it used to be that a sign of excessive movement is a shiny spot on the front of the intake where it is rubbing on the hood pad. You can test for mvmt with the parking brake and engaging the clutch to see how much the motor is able to move with the hood open (open eyeline to motor). Good luck with the repair!
 

Dougies for 89MTX

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Thank you guys, I was unsure of putting grease on the metal to metal contact so I did not, however when I get back to college today I will do it and check for movement. But for the record, it did fix it and I am so grateful it was this easy.
 

BaySHO Performance

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