1987 toyota supra shuttering

[canjet]

I have changed spark plugs, wires, distributor cap, rotor, and fuel filter. car still shutters at 2500-2800 rpm intermintently at all gears. supra is 5 speed manual and a non-turbo. Please, need advice.

[Yellow 13]

Are you getting a check engine light?

[canjet]

No, I am not getting a check engine light. rpms stays constant when it happens and only happens during accel, not in neutral. Does not feel like the tranny or driveshaft.

[TcmaBoy]

Have you checked the timming advance?

[canjet]

Checked timing, it is 10 degrees, good according to specs. It seems to shudder after engine is warmed up a bit. Could it be the O2 sensor.

[Yellow 13]

I think an O2 sensor would cause touble through the whole RPM range. Not just 2500-2800.

The timing marks are all correct at 10 degrees TDC? Cams and crank Im assuming.

What about the gear that connects the distibutor to the camshaft?You may have play in that, Remove the whole distibutor and check the gear on the end of the shaft and the shaft its self for any wear or play.

You may also want to check your timing belts tension, It could feel tight by hand but when its running and gets hot it tends to get a little looser.

[TcmaBoy]

Originally Posted by canjet

Checked timing, it is 10 degrees, good according to specs. It seems to shudder after engine is warmed up a bit. Could it be the O2 sensor.

Yes that is at idle. Check the advance. Have someone rev the engine through that band and make sure the timing advances smoothly. You can also watch for a misfire with the light. Check all the cylinders. Also check out the igniter and distributer.

I had a similar problem with my old 280ZX. I would get it up to 3500 and it would stumble. It turned out that the advance was off. When it hit there the timing was so far out that it was detonating.

[Yellow 13]

Originally Posted by TcmaBoy

I had a similar problem with my old 280ZX. I would get it up to 3500 and it would stumble. It turned out that the advance was off. When it hit there the timing was so far out that it was detonating.

Your talking about advance on the disributor or the crank now?

[TcmaBoy]

One other thought. DUH! Did you gap your plugs before installing them?

Originally Posted by Yellow 13

Your talking about advance on the disributor or the crank now?

??? We are not talking about assembly. We are talking about spark advance. This is mesured with a timing light while the engine is running, and not by looking at the alignment marks on the gears.

As engine speed increases the timing needs to change so that the flame front has time to spread before the piston gets to the top. If you watch the timing light when you rev the engine it will climb from 10deg to 15 to 20 and so on. The idea is to watch each cyl as you rev the engine to make sure that:

1. The pulses are a steady rythem. If they are erratic you have a misfire condition.

2. The timing advances properly. I had a map of where the timing should be for a given engien RPM, but I can't find it.

On my old 280 the distributer used a vac advance system which is a bit different from the electronic ignition on the 7MGE. On a vac advance distributer you have 2 adjustmemts. One is the adjustmemt made by rotating the distributer body. That is your idle adjust. The other is the vac advance which is usually made by turning a screw on the advance actuator.

The 7MGE monitors the CPS for engine speed and position. It then uses a timing advance map in the ECU to determine when to trigger the igniter. The idea here is to check each cyl to find out if it is a misfire or a timing problem, and if the problem exists on only a specific cyl or on all of them. The possible culprits could be the CPS, the igniter, the ECU or a wire problem. That is assuming that the parts already replaced are good and properly installed.

[Yellow 13]

But the 7MGE doesnt have a CPS I believe. It only has the regular distributor setup, while the 7MGTE has the coil pack and CPS. I always thought that the timing on the 7MGE was completely mechanical as far as firing the spark plugs.

I think...

[TcmaBoy]

No, the coil is triggered by an igniter which is controlled by the ECU. It references the tach signal and the CPS to controll spark advance.

[Yellow 13]

Ok, so the ECU sends a signal to the ignitor which sends a signal down to the distributor which then goes to the rotor and jumps to the nodes which causes a spark from the sparkplugs. For a system with a distibutor not a coil pack.

I always thought the energy for the spark waused caused by contact between the rotor and the node.

One more question, Since you can run N/A cams in a 7MGTE engine, If I were to get a 7MGTE ECU and coil pack would I be able to run my 7MGE (N/A)with a coil pack instead of using the distributor. (So long as I ran it with the 7MGTE ECU)

Edit: Oh and after I change to a turbo MAF as well sense the N/A and turbo use different ones.

[canjet]

Checked the timing advance, moved smoothly with someone on the pedal accelerating. Checked distributor, looked good also. How can I check the ignitor module? I am going to replace the timing belt and torsioner just because it is overdue. I disconnected the o2 sensor and engine responds better with less shudder. Will give update after timing belt change.

[TcmaBoy]

http://www.cygnusx1.net/supra/library/TSRM/index.html

[BIKNICKEL]

I had a similar problem and it turned out to be bad gas. Drain and replace fuel filters.